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Educational Technical Sessions

Find solutions to common project challenges and explore top-of-mind industry issues, trends and innovations at RETC. Review the RETC program and see how you can re-focus at RETC.

*Watch for updated sessions and speakers being added.

Download RETC Technical Program (current as of 4/30/2021)

Sunday, June 13 | 1:00 pm

The State of Dispute Resolution Boards in the Tunnel Industry (The Good, the Bad and the Ugly)

Tunnelers have a long history with DRB’s, as they were born of necessity in the Tunnel Industry and used for the first time on the Eisenhower Tunnel in 1974. The Dispute Resolution Board Foundation (DRBF) was formed in 1996, dedicated to promoting the avoidance and resolution of disputes worldwide, providing guidelines for the practice as well as training for DRB practitioners and participants alike. Just recently the UCA of SME and the DRBF signed a cooperative agreement, in recognition of the close ties and shared values between the two organizations. With the DRBF turning 25 this year, what better time to pause and take stock of the state of DRBs in our industry. Where have we been, where are we now and what can we expect in the future?

To share their varied perspectives on this question, we have assembled an expert panel of highly- experienced individuals with extensive experience using, or serving on, DRBs from a wide cross-section of the industry. Panelists include Mike Roach (Contractor, Traylor Brothers), David Hatem (Attorney, Donovan Hatem LLP), Joe Gildner (Owner- Sound Transit Seattle, WA), and Fred Dunham (DRB practitioner and Ex-Contractor). Session Chair Mike Vitale (Mott MacDonald?) will moderate the panel as they each provide a short talk on the subject, followed by an open panel discussion and Q&A forum. Join us for what promises to be an interesting and provocative assessment of the past, present, and future of DRBs; the good, the bad and the ugly.


Monday, June 14 | 8:30 am

Contract Practices

Chairs: James Corcoran, Traylor Bros., Inc., Frank Huber, Metro Vancouver, Burnaby, British Columbia, CA

Sponsored by: The Walsh Group

CMAR Delivery Targets Effective Management of Risks in Achieving Water Supply Objectives
Chris Mueller, Black & Veatch, Houston, Texas US; Savita Schlesinger, Loudoun Water, Ashburn, Virginia US; Sarah Lothman, Loudoun Water, Ashburn, Virginia US; Michael Hanna, Black & Veatch, Gaithersburg, Maryland US; Cary Hirner, Black & Veatch, Kansas City, Missouri US

Loudoun Water is currently implementing a quarry to reservoir conversion that will improve water supply reliability. The Milestone Quarry Project consists of an inter-tie to the existing Potomac River Pipeline; new pipeline and tunnel; and a pumped intake/outlet. In consideration of key project risks, an innovative CMAR delivery model was selected with the benefit of having the CMAR contractor work with its designer and actively participate in risk mitigation. This paper reviews the CMAR procurement process and discusses contract incentives that were adopted to promote the work within the constraints of contract law in Virginia.

Design-Build vs Design-Bid-Build. A review of Canadian recent tunneling experiences
Tamara Kondrachova, U of T, Engineering Department, Richmond Hill, Ontario CA; Giuseppe Gaspari, AECOM, Mississauga, Ontario CA

Contract practices affect cost and schedule of tunneling works, impacting risk allocation between Owners and Contractors. The Authors compiled a dataset of projects constructed in the Toronto Area between 1990-2020 procured either Design-Build or Design-Bid-Build. Data were analyzed identifying independent cost variables across the two methods. Overall industry's efficiency further comparison with historical information demonstrates the costs of engineering ongoing escalation due to rising trends in environmental requirements and public consultations stirred through modern communicative platforms. These hard to predict and estimate costs need to be included in the risks evaluated and managed by Owners and not by Contractors.

Tunneling to Manage Construction Impacts for Albany’s Beaver Creek Clean River Project, Albany, New York
Yuannian (Jerry) Wang, CDM Smith, Boston, Massachusetts US; Mahmood Khwaja, CDM Smith, Boston, Massachusetts US; Michael Schultz, CDM Smith, Boston, Massachusetts US; Greg Bold, CDM Smith, Latham, New York US; William Simcoe, City of Albany Department of Water & Water Supply, Albany, New York US

Beaver Creek Clean River Project will satisfy the consent decree requirements by capturing and treating combined sewage overflows. The project consists of, approximately, 2,700 feet of 30-inch trenchless pipe installation, a new screening/disinfecting facility, an expansion of an existing diversion structure, and a 72-in internal diameter, 550-foot long mined tunnel. The tunnel portions are being progressed as early release packages. This paper presents the geotechnical exploration program and the subsurface conditions encountered; interpretation of the geotechnical conditions; and, approach to developing stand-alone packages for the tunnels to mitigate construction and schedule risks and continue to advance the project.

Case Study of EPB-TBM Crossing through Boulder Cluster and Method Selected for Claim Resolution
Keivan Pak Iman, GHD, Markham, Ontario CA

Historically, boulders are a frequent source of problem in soft ground tunneling. It is important to attempt to make an assessment of the nature and quantity of the boulders, although in many cases, it will be impossible to do so with great accuracy. Boulders, can pose major problems for TBMs in terms of slowing down or halting the tunnel advance, cutter damage, and abrasive wear. Although proper selection of the TBM and the cutterhead can manage the risk, ground uncertainties still cannot be eliminated. The paper reviews a case study of a 3480 mm diameter EPB-TBM utilized for completion of 2.5 KM tunnel in Glacial Till, crossing the CP railway, HWY 401, a creek, and a confined aquifer. Alignment consists of multiple horizontal curves including small radius curves (r=210 m) at shafts breakthrough. An unexpected boulder cluster lead the contractor to experience extreme damages to the screw conveyor, RFJ system and causing a crack in main motor plate which resulted in losing one of the six main motors. This paper reviews contractor’s solutions and includes discussion on specific claim resolution method used in this project which can be of great value in preparation of specification and GBR for similar projects.

Differing Site Conditions and Dispute Avoidance Under the FIDIC Emerald Book for Underground Works
Juerg Kuenzle, Office for Construction Dispute Resolution, Bern 8, Bern CH

In 2019, the International Federation of Consulting Engineers (FIDIC), in collaboration with the International Tunneling and Underground Space Association (ITA), published its first contract specifically designed for underground works, the so-called Emerald Book. Based on the proven principles of the other FIDIC contracts, the Emerald Book addresses many of the issues to which underground projects may give rise, including those pertaining to differing site conditions (DSC, which FIDIC calls “Unforeseeable Physical Conditions”). The DSC-related clauses in the Emerald Book define a straightforward project and contract management process around the “Geotechnical Baseline Report” (GBR). The Emerald Book connects this process to an elaborate dispute avoidance mechanism, which involves not only the owner (which FIDIC calls “Employer”) and the contractor, but also the “Engineer” retained by the owner and the Dispute Avoidance & Adjudication Board (DAAB). This paper deals with the avoidance of DSC-related disputes under the Emerald Book, with particular attention to infrastructure projects involving multiple parties and multiple contracts. It is intended to provide the reader with a practice-oriented insight into international contracting and dispute avoidance practices.




Chairs: Nick Bower, Traylor Bros., Inc., Long Beach, California, US, Richard Giffen, US

Influence of Large Deep Excavations on Closely Underlying Subway Tunnels and Design of Mitigation Measures
Shawn Wang, AECOM, Thornhill, Ontario CA; Giuseppe Gaspari, AECOM, Mississauga, Ontario CA

The pandemic emergency is forcing transit agencies to define strategies allowing social distancing, that are more challenging in underground interchange stations in crowded downtown cores. TTC’s Bloor-Yonge Station Capacity Improvement Project in Toronto was approved to meet increasing demand and represents an opportunity to fight Covid-19. This paper discusses cost-effective solutions in expanding the cut-and-cover station box over existing Toronto Subway Line 2 and connecting it through openings in the steel-plates tunnel liner. Potential uplift risks and structural damage due to minimal vertical clearance were analyzed via three-dimensional finite element analyses with advanced constitutive laws to simulate the multi-stage construction process. Based on the simulation results, a series of countermeasures, including excavation support systems, king posts, ground-consolidations, and liner reinforcements were integrated into a comprehensive design to ensure the serviceability and structural integrity of the subway tunnels.

Tunnel Induced Settlement and Impact Analysis Automation and 3D Visualization
Frank Cesario, Jacobs, Toronto, Ontario CA; Brian Boye, Jacobs, Cardiff, Cardiff GB; John Kinnear, Jacobs, Toronto, Ontario CA; Camilo Quintero, Jacobs, Toronto, Ontario CA; Bashir Ahmed, City of Toronto, Toronto, Ontario CA

In this paper, a novel approach is adopted in automatically calculating effects of tunnel induced settlement on buildings and utilities. This approach results in increased output quality, consistency, time / cost saving and ability to respond quickly to design changes. This approach was applied to the planned Fairbanks Silverthorn Storm Trunk Sewer System project, located within the City of Toronto. The automation allowed a very large area of topography, tunnels (6km), buildings (9000) and utilities (over 1000) to be evaluated. The visualization of the settlement and impacts allowed designers to optimize the design to mitigate the impacts of the settlement.

Design and Construction Challenges at the Potomac River Tunnel in Washington DC
Colin Lavassar, McMillen Jacobs, Washington, District of Columbia US; Moussa Wone, DC Water, Washington DC, District of Columbia US; William Edgerton, McMillen Jacobs, Washington, District of Columbia US; Martino Scialpi, McMillen Jacobs, Washington, District of Columbia US

The Potomac River Tunnel (PRT) is the next major phase of the DC Clean Rivers Project. The PRT includes a 5.5-mile-long, 18-foot-diameter tunnel, seven shafts, and two underground connections to existing structures. Major challenges include TBM excavation though mixed-face conditions within a buried paleo-channel and a 2,000-foot-long rock/soil transition zone; construction beneath the elevated Whitehurst Freeway; tunneling beneath an existing luxury residential building and existing transit tunnels with limited clearance; and complex coordination with a variety of federal, regional, and local stakeholders. This paper describes the overall project scope, geotechnical conditions along the alignment, and primary design/construction challenges and mitigations.

Tunnel Lining Design in Active Fault Zone: Case Histories and Innovations
Peter Chou, Parsons, Oakland, California US; Pooyan Asadollahi, Parsons, DC Washington, District of Columbia US; Danny Lin, Parsons, Boston, Massachusetts US

To maintain flexibility and ductility of tunnel crossings through active faults, various mitigation measures are being used depending on fault displacements and seismic design criteria. Examples of those approaches are (a) simple bell and spigot joint; or (b) complex deformable longitudinal bolt and spring joint system with seismic isolation washer. This paper provides a summary of tunnel fault crossing design using our previous relevant experiences in California as well as case histories from Japan, Taiwan, Turkey and Italy found in literatures. Comparisons are made between large and small diameter tunnels, transportation and utility tunnels, as well as bored, mined and cut-and-cover tunnels. Recent innovations, such as Japanese and Italian techniques, for tunnels crossing active faults are also discussed.

Tunneling Under Pleasure Bay with an Open-Face TBM
Tao Jiang, Hazen and Sawyer, Alpharetta, Georgia US; Joshua Farmer, Hazen and Sawyer, Raleigh, North Carolina US; William Gettings, Hazen and Sawyer, Edison, New Jersey US; Michael Gianforte, Two Rivers Water Reclamation Authority, Monmouth Beach, New Jersey US

The Two Rivers Water Reclamation Authority in Monmouth County, New Jersey, is replacing its aging Pleasure Bay Interceptor with a new 54-in interceptor in a 3,250-foot long 10-foot diameter tunnel and a new 50-mgd pump station. A comprehensive phased geotechnical investigation was performed, including SPTs, CPTs and geophysics, a channel filled with soft marine sediments was identified. The tunnel is set in stiff to hard clay/silt to enable using a less expensive open-face TBM. The thickness of tunnel cover under the channel is optimized through numerical analyses to avoid a deeper pump station yet maintain tunnel stability with controllable seepage.


Difficult Ground

Chairs: Ehsan Alavi, Jay Dee Contractors, Livonia, Michigan, US
Everett Litton, WSP, St. Louis, Missouri, US

Tunneling Through a Buried Valley with A Hard Rock EPB Compatible TBM
William Hodder, Jay Dee Contractors Inc, Toronto, Ontario CA; Ehsan Alavi, Jay Dee Contractors Inc, Toronto, Ontario CA; Nader Ghasempour, Jay Dee Contractors Inc, Toronto, Ontario CA; Daniel Cressman, Black & Veatch Canada, Toronto, Ontario CA

The Coxwell Bypass Tunnel is expected to be excavated entirely through Georgian Bay shale, at 50 meters deep. The tunnel alignment runs parallel to a buried bedrock valley located adjacent to Bayview Avenue. The tunnel crosses this valley in the southern portion of the alignment, adjacent to the Don River. The risk of encountering weathered bedrock, significant ground water inflows or surficial soil deposits through this area was identified as a significant risk and the TBM has been designed with the ability to probe drill ahead of the TBM and convert to EPB mode if necessary. This paper will discuss the additional exploration that was performed by the contractor to identify the extent of this buried valley, the plan going into the zone of potential weathered shale, and the actual conditions encountered.

Transitioning from Mixed-face Conditions to Hard Rock During TBM Launch on the Reedy River Basin Sewer Tunnel Project - Greenville, SC
Horry Parker Jr., Black & Veatch, Greenville, South Carolina US; Jason Gillespie, Renewable Water Resources, Greenville, South Carolina US; Stephen O'Connell, Black & Veatch, Greenville, South Carolina US; Justin Kolster, Super Excavators, Menomonee Falls, Wisconsin US

Construction of the 5932-ft Reedy River Basin Sewer Tunnel in Greenville, SC was marked by a critical transition from drill-and-blast mining in mixed-face conditions to TBM excavation with limited rock coverage. In this paper, we discuss the geological, geotechnical, and risk management considerations for transitioning to TBM operations in variably weathered gneissic bedrock. After construction of an unexpected 230-ft starter tunnel due to differing ground conditions, the 11-ft diameter TBM was successfully launched in December 2019 without significant ground support issues. This project highlights the effectiveness of extensive rock probing to fully characterize bedrock topography prior to the TBM launch.

Mechanism of Advancing Drift on Weak Ground Excavation
Nobuharu Isago, Dept of Civil and Environmental Eng., Tokyo Metropolitan University, Hachiouji, Tokyo JP; Karen Shinoda, Tokyo Metropolitan University, Hachiouji, Tokyo JP; Sadatoshi Oomori, Penta-Ocean Construction Co., LTD., Bunkyou-ku, Tokyo JP; Tadashi Okabe, KFC  Co., LTD., Minato-ku, Tokyo JP; Ayako Gomi, KFC  Co., LTD., Minato-ku, Tokyo JP

In recent years, drift advancing method has been adopted for construction of tunnel with conventional method when the stability of whole structure cannot be ensured by full face excavation or when the effect of release of earth pressure must be expected in swelling and squeezing ground. And its mechanical behavior has been partly examined by three-dimensional numerical analysis with actual measurement data but most are applicable to each construction case. The effect of widening excavation of the drift on the degree of support members was clarified depending on ground condition when drift advancing method was used.

Under Pressure: Geotechnical Forces and Conditions at Work on The Ohio River Tunnel Project
Ross Goodman, J.F. Shea, Louisville, Kentucky US; Jesse Salai, J.F. Shea, Louisville, Kentucky US

The Ohio River Tunnel Project encountered multiple unexpected geotechnical challenges such as crown and invert instability due to the over stress condition affecting the strata above, below, and in the tunnel alignment during and after TBM excavation along with the potential for methane inflow. This paper showcases how the orientation of a tunnel alignment has a significant impact on how in-situ geological stress can impact the excavation of a tunnel from the contractor’s point of view and how geological features influence gas inflow to the alignment over time.

Rock Tunnels at High Water Pressure: Non-Continuous Pressurized TBMs vs. Slurry
Brad Grothen, The Robbins Company, Kent, Ohio US; Lok Home, The Robbins Company, Solon, Ohio US

The choice of TBM type is never easy, but it becomes especially challenging when faced with a hard rock tunnel with expected high water pressure. While Slurry Shield tunneling has a long history of addressing this problem, this method has not always been problem-free. At recent projects around the world, another method has been proven: Shielded, Non-Continuous Pressurized (NCP)-TBM tunneling in rock with a comprehensive grouting program. In this paper, the authors will analyze the use of Shielded NCP TBMs at projects around the world as compared with slurry shield tunneling in rock under water pressure. Recommendations will be given in order to establish a clear picture of the optimal tunneling method.

Hard Rock TBMs and Tunnels

Chairs: Colin Sessions, Jacobs Engineering, Atlanta, Georgia, US, Jesse Salai, J.F. Shea, Walnut, California, US

TBM Data and Performance Monitoring on Large Diameter TBM Tunnels Lined with Shotcrete in the Himalayas – A Case Study
Gary Peach, Multiconsult AS, OXFORD, Oxfordshire GB; Peter Mason, Stantec UK Ltd, High Wycombe,, Buckinghamshire GB

Planning and estimating progress rates and costs for tunneling is always best done on the basis of experience and historic precedent. Much precedent is available but the use of data monitoring, data mining and other retrieval techniques on modern TBM machines can enable this to be further expanded and refined. Advance rates can be related much more closely to rock types as can associate rock bolt and mesh/shotcrete requirements. This in turn can lead to a further refinement in best likely combinations of equipment, such as shotcrete jumbos, better selected for the anticipated conditions, rather than the potential advance rates of the machine. Efficient and timely construction of the tunnel will also be linked to times needed for finishing work. Indeed, this in turn may affect the most preferable layout and construction details of the permanent tunnel. Considerable experience has been gained in the use of two large diameter TBM tunnel drives through the Himalayas at the Neelum-Jhelum hydropower project in Pakistan. All the above aspects will be discussed in the paper based on the considerable experience and data which came from that operation, including appropriate measures in highly stressed areas potentially subject to rock burst.

Effect of Muck Transportation System on Overall Machine Performance
Anuradha Khetwal, Colorado School of Mines, Golden, Colorado US; Jamal Rostami, Colorado School of Mines, Golden, Colorado US; Priscilla Nelson, Colorado School of Mines, Golden, Colorado US

Underground construction has become a necessity considering social, technological, economical and sustainable advancements of society. Tunnel boring machines (TBMs) can be considered as an efficient method of tunneling because of high potential productivity and applicability in a variety of subsurface conditions. The muck transportation system plays a significant role in overall performance of the machine. This paper compares two different muck transportation system i.e. conveyor and train under similar geological conditions to identify the criticality of the transportation system in estimation of machine utilization. The results show the applicability and extent of redundancy in the use of the two systems.

The Effect of TBM Diameter on Ring Installation Time
Tala Tahernia, Colorado School of Mines, Golden, Colorado US; Jamal Rostami, Colorado School of Mines, Golden, Colorado US

TBM performance prediction is critical for developing a reliable estimate of the construction completion time and cost of the tunnel. Machine performance is affected by machine type and specification, geological condition, site setup and logistics, and operational factors. These factors lead to scheduled and unexpected downtimes during the tunnel construction. The effect of different parameters on TBM performance was studied by many researchers; however, the effect of tunnel size was never investigated thoroughly. This paper concentrates on the effect of tunnel diameter on the type and duration of downtimes and examines the impact of machine diameter on downtimes. For this purpose, the operational parameters and their dependency on diameter are analyzed. Furthermore, two tunnels with different diameters and similar TBM type were compared as case history to evaluate the capability of the proposed analysis method for predicting TBM performance based on machine diameter.

Tunneling in Toronto Shale- Construction of Coxwell Bypass Tunnel Project
Daniel Cressman, Black & Veatch, Markham, Ontario CA; Ehsan Alavi, JayDee Canada, Toronto, Ontario CA; Tatiana Chiesa, City of Toronto, Toronto, Ontario CA; Robert Mayberry, City of Toronto, Toronto, Ontario CA

The City of Toronto’s Coxwell Bypass Tunnel (CBT) is currently being constructed by North Tunnel Constructors ULC. The scope of the CBT project includes construction of approximately 10.5 km of of 6.3 metre finished diameter rock tunnel, five 20 metre diameter storage shafts and eleven tunnel connection drop shafts, along with associated deaeration and adit tunnels. This paper describes progress on the CBT to date and reviews the approach taken in both design and construction of the tunnels and shafts to mitigate risks and reduce cost and schedule of construction.

Utilizing “Big Tex” for the Dallas Mill Creek Drainage Relief Tunnel
Paul Smith, Black & Veatch Corporation, Richardson, Texas US; Milton Brooks, City of Dallas, Dallas, Texas US; Quang Tran, Southland Holdings, LLC, Roanoke, Texas US; Euadomar Silva, Black & Veatch Corporation, Dallas, Texas US

The Dallas Mill Creek Drainage Relief Tunnel is an 8.04 km (5 mile) tunnel that will provide 100-year flood protection for impacted neighborhoods in the east Dallas area. “Big Tex” is a main beam gripper TBM capable of changing diameters in mid-tunnel to excavate 2.83 km (9,290 ft) of 11.45 m (37.58 ft) diameter tunnel and 5.21 km (17,095 LF) of 9.94 m (32.61 ft) diameter tunnel. Construction began in April 2018 and is anticipated to be completed in late 2023. This paper will discuss the challenges and lessons learned during assembly and re-assembly, start-up and mining with “Big Tex”.

The Bypass Tunnel: Excavation, Interliner, and Lining
Ted Dowey, NYC DEP, Pound Ridge, New York US; Sean McAndrew, New York City Dept. of Environmental Protection, Elmhurst, New York US; Grant Miliner, Keiwit, Marlboro, New York US; Eric Jordan, Parsons, Marlboro, New York US; Schmitt George, New York City DEP, Marlboro, New York US

The Rondout-West Branch Bypass Tunnel is being built to bypass a substantial leak in New York City’s primary water supply tunnel. The 13,500 foot long tunnel travels 600 feet under the Hudson River through the same troubled geology and high pressure water inflows that the original tunnel did in the 1940’s. A Robbins TBM traversed this geology and built gasketed segments. Nine thousand two hundred feet of 16 foot diameter interliner was installed and backfilled within the segments. Finally, reinforced cast in place lining was placed. This paper addresses the challenges, and the multi-tasking approach the contractor utilized.



Monday, June 14 | 1:30 pm

Design Build Projects

Chairs: Kush Chohan, McMillen Jacobs Associates, Walnut Creek, California, US, Dillon Tew, Traylor Bros., Inc., Santa Clarita, California, US

Sponsored by: HNTB

Construction of Ottawa's Combined Sewage Storage Tunnel
Andreas Feiersinger, Dr Sauer & Partners Ltd., Surbiton, Surrey GB

The Combined Sewage Storage Tunnel (CSST) is part of the Ottawa River Action Plan and will greatly reduce the frequency of sewage overflows into the Ottawa River during storms. The project consists of the design and construction of two TBM tunnels running east west and north south along 6.2 km in total, and multiple shafts and support buildings. Contractor Dragados Tomlinson JV (DTJV) was awarded the $232 million CAD contract in 2016 and the CSST will be in operation in 2020. The paper will address TBM selection, critical tunnel sections, geotechnical risk management, rock mass grouting and other aspects.

Design of Precast Segmental Tunnel Lining in a Design-Build Environment
Irwan Halim, AECOM, Chelmsford, Massachusetts US

Nowadays more infrastructure tunnel projects are procured using design-build method. In this environment, the Owner’s engineer would typically provide performance requirements for the design-builder, and the Contractor’s designer would work with the contractor to design the tunnel lining based on the Contractor’s means and methods and manufacturing process. This paper will describe the typical requirements provided by the Owner based on its design objectives, and the means and methods by the Contractor that would significantly impact the design. Project examples and recommendations for Owner’s requirements will be provided that can optimize the design and still achieve the Owner’s performance objectives.

Courthouse Commons Inmate Transfer Tunnel.  Tunneling through San Diego using Alternative Delivery
Sam Lo Grasso, Mott MacDonald, Los Angeles, California US; Stuart Warren, Mott MacDonald, Los Angeles, California US; Carlos Herranz Calvo, Mott MacDonald, Los Angeles, California US; Ted Gelsing, Project Management Advisors, Inc., Solana Beach, California US; Charley Marchesano, County of San Diego, San Diego, California US

Mott MacDonald and Project Management Advisors are providing Technical and Project Management services for San Diego County for the Courthouse Commons Project. The Courthouse Commons project involves the redevelopment of three downtown blocks owned by San Diego County and construction of an Inmate Transfer Tunnel between the County Central Jail and the San Diego Central Court. The tunnel will be 327 feet, will cross the San Diego Fault and will be constructed using SEM. This paper discusses the history and procurement strategy for the project, the technical aspects of the transfer tunnel and the construction of the tunnel to date.

Design and Construction of the new I-75 Modernization Stormwater Storage and Drainage Tunnel System in the Segment 3 P3 DBFM Contract
David Mast, AECOM, Cleveland, Ohio US; Mina Shinouda, Jay Dee Contractors, Inc., Livonia, Michigan US; Amanda Foote, AECOM, Cleveland, Ohio US; Jason Edberg, NTH Consultants, Ltd., Detroit, Michigan US

The Michigan DOT’s I-75 Modernization Project, Segment 3, is a 30-year, $1.2 Billion design-build-finance-maintain project in Southeast Michigan. The scope includes building a nearly 4-mile long, 14.5-foot ID stormwater storage tunnel. The tunnel and pump station are being built concurrent with new roads and bridges, requiring multiple levels of design and construction coordination. Underground risks include the potential for encountering granular soils, groundwater, and explosive gases. The new tunnel will be mined by a new open-face TBM and lined with a one-pass steel-fiber-reinforced precast concrete segmental lining. Shaft construction began in early 2020 and tunnel mining in July 2020.

A New Technical Challenge for Variable Density Type TBMs
Alejandro Sanz, gGravity Engineering, Madrid, Madrid ES; David Mazeyrie, Vinci Construction Grand projects, Rueil-Malmaison Cedex, Paris FR; Juan Luis Magro, Dragados S.A., Madrid, Madrid ES; Taner Aydogmus, Flatiron Constructors, Inc, Broomfield, Colorado US; Yvonnick Rescamps, Vinci Construction, Norfolk, Virginia US

The HRBT Expansion Project initiated by VDOT will add two 1.5-mile TBM bored tunnels to the existing two immersed-tube tunnels between artificial islands, part of the connection between Norfolk and Hampton across the Chesapeake Bay in Virginia, USA. The new bored tunnels will be built by Hampton Roads Connector Partners (HRCP), a joint venture of Dragados USA, Vinci Construction, Flatiron Constructors and Dodin Campenon Bernard. This paper covers technical discussions that led HRCP to select a Variable Density TBM to address the challenges of this tunnel project

Ground Control Approaches and Methods

Stephen Njoloma, JCK Underground, Cary, North Carolina, US, Amitabha Mukherjee, WSP, Bellerose, New York, US

Sponsored by: Hatch

The Use of Low-Density Cellular Concrete (LDCC) in Annular Fill Applications: Kaneohe-Kailua Sewer Tunnel Case Study
Nico Sutmoller, Aerix Industries, Timberville, Virginia US; Don Painter, Brierley Associates, Honolulu, Virginia US

This paper will address the feasibility of using low-density cellular concrete (LDCC) in annular fill applications. In this discussion, the paper will examine the case study of the Kaneohe-Kailua Sewer Tunnel project that was constructed in 2018 to convey wastewater and provide temporary storage of peak wet weather flows entering the collection system, thereby reducing the potential for spills. Located on the island of Oahu, Hawaii, the 13’-0” excavated diameter with a 126” Hobas pipe installed as the final liner for the conveyance tunnel extends for approximately three miles from the Kaneohe Pre-Treatment Facility to the Kailua Regional Wastewater Treatment Plant. The paper will also evaluate data related to the physical properties, manufacture, and technological advances of LDCC, highlighting the material’s unique physical properties of low density, high compressive strength, environmental stability, and high fluidity during placement. In its discussion of the Kaneohe-Kailua Sewer Tunnel project, the paper will posit the effectiveness of 50 LDCC as a backfill material in annular fill projects.

Automatic Computation of TBM Face Pressure using 3D Ground Model
CK Tsang, Aurecon, Melbourne, Victoria AU; Jack Muir, Aurecon, Melbourne, Victoria AU; Joshua Barry, Aurecon, Melbourne, Victoria AU

Correct face pressure is critical to safe operation of a closed face TBM. If inadequate face pressure is applied, this will lead to excessive ground movement, and may result in collapse of the tunnel face. Face pressure calculations are performed manually every few meters along the tunnel alignment. With the application of a 3D ground model, ground profile information can be extracted for automatic computation. This will significantly improve the efficiency and accuracy and is adaptable to changes in design parameters. This paper will discuss the development of automatic computation techniques in extracting information from a 3D ground model.

Tunneling Under Highway 401: Construction of Large Diameter Pre-Support Pipe Canopy
Tyler Lahti, R.V. Anderson Associates Limited, Toronto, Ontario CA; Mary Jane Ferraro, Toronto Tunnel Partners, Etobicoke, Ontario CA; Prakash Nadesparan, R.V. Anderson Associates Limited, Toronto, Ontario CA

Two new tunnels are being constructed under the Highway 401 & 409 interchange to accommodate additional tracks and future electrification required for Metrolinx’s GO Expansion program. The new tunnels are being constructed using the Sequential Excavation Method (SEM) and utilize a tunnel pre-support system consisting of a series of 813mm diameter steel pipes to form a pipe canopy. The pre-support pipes were installed with an Auger Boring Machine (ABM) in four separate headings; one heading from each of the tunnel end portals, and two from a shaft in the middle of the highway. To facilitate the auger boring operation, a custom steel frame was required to counteract the 320 tonne thrust from the ABM at the portals, and a temporary shaft structure was installed in a narrow median space of the highway. The installation of the pipe canopy had to overcome challenges including removal of obstructions, alignment issues, and controlling settlements to the highway surface. This paper discusses the purpose of the pipe canopy, design and installation of the temporary shaft and structures to support the auger boring operation, the experience of the contractor during the installation of the pipes and brief overview of the experience tunneling below the pipes.

Advance Rates in Soft Ground Tunneling
Dan Ifrim, Hatch, Mississauga, Ontario CA; Don Del Nero, Hatch, Pittsburgh, Pennsylvania US

Soft ground tunneling poses major challenges to the underground industry. Most of soft ground tunnels are in highly urbanized areas, often include limited cover, and include a strong trend of increasing diameters. Therefore, soft ground tunneling works can sometimes cause inevitable ground movements and settlements that may lead to damages to adjacent buildings, roads, structures or utilities; many of these being “lifeline” infrastructure assets. Tunneling operations, TBM advance rates, and face pressure control can significantly increase or decrease such risks, depending on how well the TBM and operational parameters are applied to the ground conditions. Additionally, the risks of impacting existing infrastructure are heightened in many parts of North America because of cobbles and boulders. To date there is no standardized guideline that determines appropriate tunneling rates nor operator’s guidelines, to ensure safe tunnelling in soft ground. The paper analyzes tunneling records from completed soft ground tunnels to determine a relation between ground conditions, tunnel cover, TBM cutters maintenance and TBM advance rates. The records are discussed to draw several mitigation measures to be adopted during tunnelling, to reduce risks of settlements, over excavation or sinkholes.

Grouting Cast-In-Place Concrete Tunnel Liners—What Have We Learned?
Adam Bedell, Stantec, Atlanta, Georgia US; Brad Crenshaw, GEC Drilling and Grouting, Jefferson City, Tennessee US; Paul Derby, Xypex Chemical Corporation, Acworth, Georgia US

Modified contact grouting was introduced almost 10 years ago as a methodology combing traditional contact grouting and consolidation grouting to address groundwater infiltration into hard rock tunnels that utilize cast-in-place concrete as permanent tunnel support. This process has been used on additional tunnels (since initially presented) as a measure to mitigate both groundwater infiltration and exfiltration. During this time, self-sealing grouts have been developed and have been added to the process to further reduce groundwater infiltration that occurs through cracks and discontinuities within the concrete liner itself. This modification is presented and additional results from the grouting process are discussed.

Design and Construction of Load Transfer System to Replace Existing 39th Street Bridge Piers with New Integral on the Track B/C Approach Structure for the East Side Access Project
Julio C. Martinez, Skanska USA Civil Northeast, New York, New York, US; Jeffrey Rice, WSP, New York, New York, US; Hayden Weschler, Skanska USA Civil Northeast, New York, New York, US

The underpinning/SOE support required the construction of 16 large hand dug pits 36ft deep that were reinforced and concrete filled. In addition, an extensive steel support system was tied into the bridge super structure. All of the underpinning/tunnel construction was done while a 110ton crane sat directly atop the heavily trafficked – 66 ft. wide bridge. The tunnel excavation, concrete lining and final bridge pier support work will also be presented. All work was done within 5ft of active mainline tracks and that required tight grouting behind all lagging to eliminate any track settlement.


Health & Safety and Sustainability

Chairs: Colin Lyons, Kiewit, Omaha, Nebraska, US, Andrew Bursey, Jacobs Engineering, Atlanta, Georgia, US

Slurry Treatment Plants in Mechanized Tunneling Operations – Safety, Boosting and Cost Factor for Jobsites
Gino Vogt, Herrenknecht AG, Schwanau, Baden-Wurttemberg DE

In world wide mechanized tunneling operations time, consumption figures and safety requirements are the main factors for the jobsites. These highly effect the budgets. One of the most important components, often underrated, effecting these factors especially in slurry TBM operations are Slurry Treatment Plants (STPs). Wrongly sized and designed STPs create bottle necks to the operation and finally could delay the whole schedule. Inefficiened planned STPs create huge consumption figures in power, bentonite, water and polymers, etc. which will raise the budget cost dramatically. Inaccurate designed and treated slurry properties could cause a risk potential for the whole job. This presentation will explain the key parameters for STPS to look at from the start to the end of the project and its results.

Lyon Metro Line B Extension: A Variable Density TBM for an Underground Mission in Remarkably Diverse Geology
Karin Bäppler, Herrenknecht AG, Schwanau, Baden-Wurttemberg DE

Lyon Metro Line B with a length of 2.4km will support sustainable urban development for the metropolitan area of Lyon and is being built in singular diverse geology. The project sets a benchmark for the use of Variable-Density-TBM-technology in forecasting geological conditions along the tunnel route. They comprise sections of highly permeable and extremely highly abrasive alluvial deposits that will be excavated mainly above the water table and areas with fresh granite with UCS of up to 164 MPa. The paper will highlight on this special area of application and its benefits in regards of safety, quality and required space.

Steady-State Groundwater Inflows in Deep Rock Tunnels
Dr. Mark J. Vanarelli, Colorado School of Mines, Golden, Colorado US

Estimating groundwater inflows in rock deep tunnels is critical to the safety of personnel constructing the tunnel and the cost of construction. A semi-empirical procedure was utilized for estimating groundwater inflows into two deep rock tunnels. The Chattahoochee and Nancy Creek tunnels are deep rock tunnels which exhibit radial flow conditions. The statistical analysis presented in this paper indicates that the semi-empirical procedure works well; however, variations in the procedure and/or an insufficient amount of testing could lead to underestimations of the inflow quantities. Modeling using Monte Carlo simulations was an effective tool for improving the groundwater inflow estimates.

Respirable Crystalline Silica Dust (RCS) - Practical Impacts and Solutions in Tunnelling
Rainer Antretter, BeMo Tunnelling, Innsbruck, Tyrol AT

While RCS that arises in industrial production mostly accumulates out of a point source and can be extracted well, the application of this method is much more difficult in underground construction, since dust does not only occur locally, but largely spread. Analysis of dust measurements show that RCS values are difficult to predict and effective dedusting systems are required to comply with the limit values (PEL) in breathing air. Dedusting systems are effective at the face area, while dedusting of working areas behind is difficult or even impossible. In tunnels with small cross-sections dedusting systems often cannot be accommodated and PPE must be used instead. The paper highlights problems with dedusting measures and shows possibilities to comply.

Dustless Hard Rock Tunneling Methods
Michel Wasag, Jay Dee Contractors, Livonia, Michigan US; Homer Scurlock, Jay Dee Contractors Inc., Livonia, Michigan US; Cody Giroux, North Tunneling Constructors ULC, Toronto, Ontario CA

Silica/Crystalline Quartz exposure remains a serious threat to nearly 2 million U.S. workers, including more than 100,000 workers in high risk jobs such as abrasive blasting, foundry work, stonecutting, rock drilling, quarry work and tunneling. The primary focus of this study is to reduce dusty air (crude air) and limit/eliminate potential respirable dust (Silica/Crystalline Quartz) exposure to tunneling personnel by introducing two de-dusting methods/systems. The study is being conducted on two separate tunneling projects. The first project location in Toronto, Ontario, Canada will be utilizing a wet de-dusting system and the second project in Cleveland, Ohio will be utilizing a dry de-dusting system. The goal is to determine which de-dusting system application is best suitable to reduce/remove/capture the aspirated, dry and fine-grained dust particulates within the tunnel heading.


Shafts and Mining

Chairs: Aaron McClellan, Kiewit, Omaha, Nebraska, US, Eric Levonas, Drilltech Mining and Tunneling, Antioch, California, US

Sponsored by: The Walsh Group

Real Challenges of Digging a Shaft in Free Phase Oil and Hydrocarbons
Ehsan Alavi, Jay Dee Contractors, Inc., Livonia, Michigan US; Savreet Singh, C&M McNally Tunnel Constructors, Burlington, Ontario CA; Sanjeer Yogendran, C&M McNally Tunnel Constructors, Burlington, Ontario CA; John Teahen, C&M McNally Tunnel Constructors, Burlington, Ontario CA

The Don River & Central Waterfront Coxwell Sanitary Bypass Tunnel Project in Toronto will extend approximately 10.5 km from Ashbridges Bay Treatment Plant west under Lake Shore Boulevard, north under Bayview Avenue and east through the Don River park area to the Coxwell Ravine Park. During the installation of initial support of excavation and excavation of Shaft LDS-3(B), significant volumes of free phase oil and hydrocarbon contaminants were found in both overburden and the transition zone between rock and overburden. Due to the heavy inflows of the contaminants, excavation was stopped at the transition depth. The initial support of excavation needed to be redesigned, shaft had to be backfilled with CDF and installation of deeper secant piles are in progress to cut off contaminants. This paper outlines the initial plan for excavation as well as the design changes to the plan. The current status of the shaft excavation and lessons learned will be discussed.

Unreinforced Slurry Walls as Temporary Support of Excavation for Shafts
Pooyan Asadollahi, Parsons, Washington, District of Columbia US

Slurry walls, also known as diaphragm walls, are commonly used as temporary and/or permanent support of excavation for construction of shafts in soft ground. Through case history, this paper demonstrates economical benefits of disregarding long-term structural contribution of the slurry walls particularly in severe environmental condition. In addition, for temporary slurry wall shaft systems, possibility of using steel fiber, synthetic fiber or additives in lieu of temperature/shrinkage reinforcement is discussed with detailed analysis. Finally, the paper will be concluded by introducing unreinforced slurry wall shaft system using newly developed/patented concrete additive.

Deep Portal Shafts of the Annacis Island Outfall Tunnels – Building on Pacific Northwest Shaft Design Experience
Ulf Gwildis, CDM Smith, Bellevue, Washington US; John Newby, CDM Smith, Burnaby, British Columbia CA; Fred Marquis, McMillen Jacobs Associates, Vancouver, British Columbia CA

From the Brightwater Conveyance System in Seattle to the Second Narrows Water Supply Tunnel in Vancouver, B.C., the construction of deep lying tunnels in the Pacific Northwest has required the design of deep portal shafts. Alluvium overlying marine and glacial deposits combined with the high regional seismicity is the common geologic setting. The latest example illustrating the development of shaft design for this scenario are the 40-m-deep shafts of the Annacis Island Wastewater Treatment Plant New Outfall System for launching and receiving a 5-m-diameter TBM. This paper presents design considerations for these shafts against the background of past project experiences.

Personnel Carriers and Conveyances in Tunnel Projects
Lauro Lacerda, Normet Americas, Inc., Layton, Utah US

Shotcrete is a highly adaptable and widely used underground construction material at infrastructure and mining projects around the world. In fact, many projects could not have been completed without its utilization. As underground projects became larger the use of mechanized wet-mix spraying gradually replaced manual dry-mix shotcrete applications. This paper details some of the reasons for that and provides information on the equipment and operational factors including safety and productivity required to successfully complete underground shotcrete projects.

Remote Vein Miner - Uncovering an opportunity for tunneling projects
Muthu Vinayak Thyagarajan, Colorado School of Mines, Golden, Colorado US; Mark Board, Hecla Mining Company, Coeur d’Alene, Idaho US; Jamal Rostami, Colorado School of Mines, Golden, Colorado US; Clayr Alexander, Hecla Mining Company, Mullan, Idaho US

In the past two decades, many major equipment manufacturers have ventured into developing new technology for underground hard rock excavation. A redesigned mobile miner, called the “Remote Vein Miner”, or RVM, has been developed by Epiroc for underground hard rock mining in Hecla’s Lucky Friday Mine. This equipment potentially opens numerous opportunities for innovation in civil tunneling projects, where the operational flexibility and accessibility of a TBM’s limited tunnel path, design and cost are limiting factors. This paper explores the application of the RVM in tunneling projects, its advantages and possible areas of innovation in tunnel planning and design.



Tuesday, June 15 | 8:30 am

Ground Support and Final Lining

Chairs: Martin Mancini, Jacobs Engineering, Florham Park, New Jersey, US, Will Hodder, Jay Dee Contractors, Toronto, Ontario, CA

A Comparison of Grouting Through Segment Ports vs Grouting Behind the Tailcan of Two Segmentally Lined Rock Tunnels
William Hodder, Jay Dee Contractors Inc, Toronto, Ontario CA; Lisa Smiley, Jay Dee Contractors, Cleveland, Ohio US; Ehsan Alavi, Jay Dee Contractors, Toronto, Ontario CA; Brian Hagan, Jay Dee Contractors, Inc., Livonia, Michigan US

The Don River & Central Waterfront Coxwell Sanitary Bypass Tunnel (CBT) Project in Toronto will extend approximately 10.5 km and lined by using a precast concrete segmental tunnel liner with an internal diameter of 6,300 mm and external diameter of 6,900 mm. The CBT liner is being grouted through ports drilled in the segments. The Westerly Storage Tunnel (WST) in Cleveland will extend approximately 2.93 km long and will be lined by using a similar precast concrete segmental tunnel liner with an internal diameter of 7,620 mm and external diameter of 8,230 mm. The WST liner was grouted using both grout ports built into the tail can of the TBM and through segments. Each tunnel was mined primarily in Shale with varying levels of weathering and both dry and wet sections. This paper will document the means and methods for grouting in each liner as well as the methods utilized to proof grout and the results found.

Final Lining Construction of an SEM Cavern- Regional Connector Transit Project
Rebecca Reeve, Traylor Bros, Inc., Long Beach, California US; Christophe Bragard, Traylor Bros, Inc., Long Beach, California US

Following the successful excavation of a 287 ft. long, 58 ft wide, and 36 ft. high SEM cavern underneath historical structures of downtown Los Angeles, an unusual three-part formwork system was used to accommodate the many unique challenges of the 18” thick cast-in-place final lining. An innovative method of hydrocarbon resistant membrane (HCR) installation was adapted using Velcro to adhere the waterproofing membrane. To further limit ground settlements, a contact grouting procedure involving grout injection to both the interior and exterior of the waterproof membrane was also implemented for the notable completion of the SEM Cavern final lining.

The Use of Structural Codes in Tunneling
Harry Asche, Aurecon, Indooroopilly, Queensland AU

Tunnels are frequently specified by owners to be designed to a structural code, often a bridge code. In the USA, AASHTO have created a tunnel code, based on structural principles, the AASHTO LRFD Tunnel Design Specification. The Load Resistance Factor Design method (LRFD) described in the AASHTO title is an approximation to the probabilistic design of structures, based on the independence of load and resistance. This methodology is well known to be problematic in geotechnical design, but it is widely used. The paper considers the LRFD approach, and describes alternative approaches that would result in more appropriate designs for tunnels.

Composite Segmental Lining to Resist a Fault Rupture
Angel Del Amo, Aldea Services, Los Angeles, California US; Bingzhi Yang, Aldea Services Inc, Frederick, Maryland US; Robert Goodfellow, Aldea Services Inc, Frederick, Maryland US; Bradley Hoffman, Aldea Services Inc, Frederick, Maryland US; Steve Redmond, Frontier Kemper Constructors Inc., Sylmar, California US

Designing and constructing tunnels in seismic prone areas present unique challenges to both designers and contractors. The Westside Purple Line Extension Project - Section 3 in Los Angeles requires crossing an active fault that may subject the tunnels to extreme structural demands. In order to guarantee that the linings will safely accommodate the fault movement, a revolutionary composite section – steel plate embedded in the intrados of the precast concrete segmental tunnel lining was finally selected. Additionally, continuous expansion steel plates over the circumferential joints will be installed to mitigate the potential opening of the circumferential joints.

TBM Removal within the Busiest Passenger Interlocking in the United States
Matthew Stokes, Skanska USA Civil Northeast, New York, New York, US; Devan Naik, Skanska USA Civil Northeast, New York, New York, US; Andy Nigro, LIRO Group, Hartsdale, New York, US

This paper describes the surgical removal of a 24ft dia. Slurry Shield TBM entombed beneath one of the country’s busiest commuter rail interlockings, the Harold Interlocking in Queens, NY, and the construction of the interface to a cut/cover tunnel which extended the mined tunnel section. A sophisticated SOE was built around the TBM to support active track loads within 8ft. of the excavation. Once the TBM head and guts were removed, a full round CIP lining was installed connecting the existing precast tunnel liner to the C/C tunnel under construction. All this construction was done on a narrow island of land without road access nestled between 7 mainline LIRR/Amtrak rail lines.

Lesson Learned During the EPB TBM Launch Using Umbilical and Muck pump
Raffaele Aliberti, The Lane Construction Corporation, Washington, District of Columbia US

The launching of a Tunnel Boring Machine (TBM) is one of the most challenging parts of the construction of a tunnel. Challenges are coming from the limited space, learning curve, for the concurrence of other activities and in some cases for the geological conditions. Launching a TBM is an extraordinary and complicated operation requiring a great level of planning. An Earth Pressure Balance (EPB) TBM was successfully launched for the Northeast Boundary Tunnel, the largest component of the Clean Rivers Project in Washington, DC. Due to space and time constraints, the 8-meter diameter TBM was launched from a single 20-meter diameter shaft, with a 30-meter-long tail tunnel by means of umbilical connections. This paper presents the steps followed during the TBM assembly and launching to allow the execution of the first drive of the tunnel maintaining high level of efficiency and quality despite the space constraints. Specifically, it focuses on the methods used to extract the excavated material (muck) from the TBM and from the tunnel, to supplying consumables, precast rings and backfill grout. The paper presents results in terms of productivity, lesson learned and possible alternatives to be considered in similar conditions.


International Projects

Chairs: Percey Townsend, J. F. Shea, Indianapolis, Indiana, US, Sebastian Sucri, Frontier Kemper

Second Narrows Water Supply Tunnel – Planning through Start of Construction
Gregg Davidson, McMillen Jacobs Associates, Pasadena, California US; Frank Huber, Metro Vancouver, Burnaby, British Columbia CA; Andrew McGlenn, McMillen Jacobs Associates, North Vancouver, British Columbia CA

The Second Narrows Water Supply Tunnel will ensure system reliability in the event of a major earthquake and increase the Greater Vancouver Water District’s capacity to meet the long-term needs of a growing population. The tunnel will be 1,100 meters (m) long and 6.5 m in diameter (3,610 lf x 21.3 ft), constructed under Burrard Inlet between North Vancouver and Burnaby in British Columbia. It will be excavated through mixed ground conditions under high groundwater pressure, using a slurry TBM, between a 72 m (236 ft) deep shaft in soil and a 110 m (361 ft) deep shaft in rock. The completed tunnel will accommodate three large-diameter water mains that will be installed as part of the tunnel contract. This paper presents the project from planning, through design and contractor procurement, and into the current construction stage describing some of the unique challenges encountered during the project development to date.

Short Startup for a High Pressure Mixshield
Matt Burdick, Traylor Bros., Inc., North Vancouver, British Columbia CA; Erica Bailey, Traylor Aecon GP, North Vancouver, British Columbia CA; Andrew Rule, Traylor Aecon GP, North Vancouver, British Columbia CA

The Second Narrows Water Supply Tunnel, Burrard Inlet Crossing project for the Greater Vancouver Water District entails deep shaft construction, subway sized pressurized face tunneling through highly variable ground conditions, installation of three permanent steel water mains and construction of elaborate valve chambers adjacent to either shaft. The paper discusses key elements of the planning and implementation of 6.69 m Ø slurry TBM assembly in a small diameter deep shaft including incorporation of a fully pressurized launch lock, preparations for saturation diving, surface support infrastructure and initial mining sequence.

The Kramer Tunnel – Challenging NATM-Tunnelling in Germany`s Alps
Richard Gradnik, BeMo Tunnelling GmbH, Innsbruck, Tyrol AT; Richard Gradnik, BeMo Tunnelling GmbH, Innsbruck, Tyrol AT; Martin Zeindl, Landesbaudirektion Bayern, München, Bavaria DE; Roland Arnold, BeMo Tunnelling GmbH, Innsbruck, Tyrol AT

The Kramer Tunnel is located in Garmisch-Partenkirchen, Bavaria in close vicinity to the Austrian border. This road tunnel project with two parallel tubes (two-lane main tunnel and separated rescue tunnel) and a length of approximately 3,600 meters passes through a rockslide area with very complicated geological and geotechnical conditions. The construction of an exploratory gallery had to be aborted in 2013 due to the difficult hydrogeological conditions in this area. SEM/ NATM in combination with groundwater lowering measures has been chosen to excavate the tunnels. The paper describes the challenges which will put the flexibility of the construction method on the edge.

Use of a GBR to Deliver Risk Management and Value – City Rail Link, Auckland
Tom Ireland, Aurecon NZ, Auckland, Auckland NZ; Phillip Kirk, Aurecon New Zealand, Auckland, Auckland NZ; Sumi Eratne, City Rail Link Limited, Auckland, Auckland NZ

The approach to Risk Management during the procurement of major projects often has a significant outcome on the ultimate successful delivery of a project. The $NZ4.4B Auckland City Rail Link project is the largest and most complex transportation project yet undertaken in New Zealand. Risk management prior and during procurement was undertaken in accordance the ITIG Code of Practice for Risk Management of Tunnel Works (TCoP) and through the use of an Alliance Geotechnical Baseline report. This paper describes the measures taken during the procurement process to achieve certainty with respect to outcomes and minimise project risks whilst also achieving value for money. This included the use of cloud-based delivery of geotechnical data and 3-D geological models, reducing tendering costs and allowing a focus on risk mitigation measures during the tender rather than data management.

Construction of an Outfall Tunnel Underneath Rio De La Plata
Mirko Martini, Webuild, Buenos Aires, Buenos Aires AR; Marcelo Benaglia, c, Buenos Aires, Buenos Aires AR; Andrea Codalli, Webuild, Buenos Aires, Buenos Aires AR

“Riachuelo - Lote 3” forms part of a sanitation programme being implemented in Argentina to relieve the “Riachuelo” river basin from its current contamination. Such scheme will expand the sewage capacity of Buenos Aires and will benefit an area of 4,3mIlions inhabitants by intercepting a number of wastewater dicharges and conveying them to a new treatment plant for final discharge into the “Rio de la Plata”. The project foresees amongst other works the construction of an onshore 48m deep shaft at the outlet of the treatment plant plus a 4,3m ID outfall tunnel of 12km length. The last 1,5km of the alignment will be fitted with 34nr vertical risers to be jacked from inside the tunnel in order to allow the discharge and dilution of the treated effluent into the river. This paper describes the peculiarities and the construction challenges of the outfall tunnel which was entirely bored under the "Rio de la Plata” using a 5.2m cut diameter EPB type Tunnel Boring Machine. The tunnel excavation faced a variety of complex conditions, such as crossing waterbearing permeable soft ground formations and advancing at a face pressure in excess of 3,5bars for the entire route.


Large Span Tunnels and Caverns

Chairs: Dave Dorfman Walsh, Little Falls, New Jersey, US, Ben DiFiore, Mott MacDonald, Cleveland, Ohio, US

Sponsored by: HNTB

Design of Large Underground Near Detector Cavern for Fermilab in Batavia, Illinois
Irwan Halim, AECOM, Chelmsford, Massachusetts US

Fermilab is constructing a large underground cavern in Limestone to house scientific equipment. The cavern will have a complex L-shaped geometry and about 215-foot depth with relatively shallow rock cover, with service/egress shafts accesses into the cavern. Three-dimensional analytical models were developed to study the ground behavior and support performance. Multiple rock constitutive and failure models were evaluated. The models were significantly impacted by the high lateral in-situ earth pressure at the site. This paper will describe the design approaches that were taken to optimize the cavern arch geometry to allow safe construction in shallow rock, and permanent support requirements.

Hybrid Metro Station for Mitigating Construction Disturbance

In busy and historic cities, traditional open box metro stations are becoming outrageously difficult, unacceptable for the citizen and uneconomical. Hybrid stations provide an interesting alternative. In-house experience of Gautrain (South Africa), West bay (Qatar), Cairo line 3A (Egypt), and Melbourne (Australia) all aim to reduce disturbance to the city and its inhabitants during construction. Constructed in rock or in soil deep under the water table, they take advantages of the latest construction techniques from cement grouting to freezing, and from traditional excavation of cavern to large TBM tunnelling. Today, they form the ultimate construction challenge.

Design and Construction Considerations for Intersecting Tunnels - Charleston, SC
Michael Miglioretti, Black & Veatch, Charleston, South Carolina US; Steven Kirk, City of Charleston, Charleston, South Carolina US; Kyle White, Black & Veatch, Charleston, South Carolina US; Lindsey Schneider, Black & Veatch, Charleston, South Carolina US; Jeffrey Kolzow, Jay Dee Contractors, Inc., Livonia, Michigan US

The US17 Spring/Fishburne Drainage Improvements Project utilizes a stormwater conveyance tunnel system of approximately 8,250-LF. The tunnel system includes two intersecting tunnels of differing diameter at a 40-degree angle. The intersection was constructed in soft-ground conditions. This paper discusses the design, geotechnical concerns, initial ground support, and final lining construction. The tunnels utilized two soft-ground TBMs excavated at 15-ft and 11-ft with ribs & lagging initial support. The final lining consisted of unreinforced and reinforced cast-in-place concrete with polymer fibers. Concrete final lining was successfully completed in March 2020.

Design and Construction of a Deep Underground Station in Urban Area
Verya Nasri, AECOM, New York, New York US; Agustin Rey, SNC Lavalin, Montreal, Quebec CA; Thomas Fortin, EBC Inc., Montreal, Quebec CA

This paper presents the design and construction of a deep underground station of the Réseau Express Métropolitain (REM) project; the Édouard Montpetit station. This is an interchange station that will connect the deeply sitting REM tracks to the existing metro station of the same name located closer to the surface. Édouard-Montpetit station is the deepest in North America. The various challenges and solutions put forth for the successful completion of this underground work are presented to serve as a valuable example for future deep excavation performed in urban area in the close vicinity of highly sensitive structures.

Major Underground Station in Montreal
Shashank Gupta, AECOM, Alameda, California US; Verya Nasri, AECOM, New York, New York US; Jaeseoung Lee, AECOM, New York, New York US; Ashish Bhargava, AECOM, New York, New York US

This paper presents the unique design and construction challenges for the Technoparc Station, located in downtown Montreal as a part of Réseau Express Métropolitain (REM), a light rail rapid transit system. The station is located 15m below the street with rock-socketed secant pile wall as the primary structural system working as both the retaining and gravity structure. The paper highlights challenges related to support of excavation structure, invert slab resisting high hydrostatic forces, waterproofing tightness etc. It also focuses on the importance of Building Information Modeling (BIM) in underground tunneling projects for effective coordination, clash-free, optimized design and costs

New and Innovative Technologies I

Chairs: Luis Fernandez-Deza, Traylor Bros., Inc., Alexandria, Virginia, US, Seth Pollak, Arup, New York, New York, US

Sponsored by: The Walsh Group

High-speed 3D Tunnel Inspection in Subway Tunnels – Case Study San Francisco BART
Heiner Kontrus, Dibit Messtechnik GmbH, Innsbruck, Tyrol AT; Jérôme Steinkühler, Dibit Messtechnik GmbH, Innsbruck, Tyrol AT; Thomas Peal, Dibit Measuring Technique USA, Inc.,, Bellevue, Washington US

The Dibit high-speed 3D scanning system which is based on Photogrammetry and LiDAR technology enables data acquisition in tunnels at a speed of up to 60mph. Given the high rate of speed the system can operate, tunnel shutdowns can be drastically reduced, and tunnel safety increased. The photorealistic texturing of the 3D-model allows the identification and analysis of smallest material damage (e.g. cracks >=0.3mm wide). The publication illustrates technical details and 3D results of the innovative system from measurements that were performed in the subway tunnels of the Bay Area Rapid Transit System in San Francisco, CA (total length 66.23km).

Segment Production 4.0 - Automated Segment Production Using Robots
Stefan Medel, Herrenknecht Formwork Technology GmbH, Schwanau, Baden-Wurttemberg DE

ROBOT SUPPORTED MOULDING – this is the name of Herrenknecht Formwork’s entry to the world of automated segment production. What had been considered impossible for a long time, has been achieved by Herrenknecht experts together with the Swiss company Marti AG: unmanned segment production on the working line. The moulds open and close autonomously with the help of a hydraulic system. A robot cleans and greases the moulds at one work station and inserts the injection sockets at another. The next step will include further automation and digital networking of all processes from production to installation in the tunnel.

Segment Design for Exceptional Circumstances: Post Tensioning & Squeezing Ground
Nick Karlin, Dragados USA, Wilmington, California US; Claudio Cimiotti, Dragados USA, Wilmington, California US; Alfonso Navarro, Sener, Madrid, Tres Cantos ES; Eduardo Velasco, Sener, Madrid, Tres Cantos ES; Alejandro Sanz Garrote, gGravity, Madrid, Madrid ES; Paz Navarro, gGravity, Madrid, Madrid ES

Dragados is currently constructing the Effluent Outfall Tunnel for the Sanitation Districts of Los Angeles; a 7 mile long effluent conveyance tunnel designed for peak flows of up to 340MGD. The contract scope includes final design of the pre-cast concrete tunnel lining, a complicated task for the two distinctive project geologies. The northern 20,000’ of the tunnel is in alluvial sands with low ground cover requiring the integration of a PCTL post tensioning system to guarantee tunnel compression. The latter 16,000’ of the tunnel will be constructed in a zone which is historically known to exhibit extreme squeezing.

InSAR Monitoring of Tunneling Surface Displacement
Ben Pantony, 3vGeomatics, Vancouver, British Columbia CA; Brian Young, Towill Inc., Concord, California US

Interferometric Synthetic Aperture Radar (InSAR) has played an integral role in many large scale tunnelling projects globally. Until recently, it has been regarded as a complementary monitoring tool. On the Los Angeles Metro Purple Line Phase 1, InSAR was proposed as a primary means to replace weekly and bi-weekly monitoring requirements on surrounding critical infrastructure. This paper will summarize the instrumentation & monitoring scope of the project, as well as the statistical analysis approach engaged in order to compare and contrast a year of historical InSAR data to known geodetic survey data, in order to utilize InSAR as an operational monitoring tool on this project.

The Variable Density TBM – Current Level of Development
Werner Burger, Herrenknecht AG, Schwanau, Baden-Wurttemberg DE

After its first introduction in 2013 the Variable Density TBMs have increased their application significantly in mechanized closed mode tunneling. Throughout a variety of successfully completed and ongoing projects since then the Variable Density TBM technology has demonstrated its advantages in a wide range of applications. The paper will present the developments and lessons learned from these projects as well as the future potential of the Variable Density TBMs.

Performance of Tunnel Segments reinforced with Synthetic Macro Fibers
Ralf Winterberg, BarChip Inc., Kurashiki City, Okayama JP; Todd Clarke, BarChip Australia Pty Ltd, Penrith, New South Wales AU

For more than a decade the tunneling industry has explored the potential and benefits of macro synthetic fiber (MSF) reinforced concrete solutions for precast tunnel segments. Parallel to industry investigations, academic research is being undertaken to better understand this material when subjected to the typical loads expected during mechanized tunneling. This paper investigates the performance of MSF reinforced precast concrete tunnel segments by means of an experimental program comprising testing of full-scale tunnel segments. The presentation of the satisfactory results of the experimental testing programme will be complemented by brief case histories from successfully executed projects, including an America’s First.



Tuesday, June 15 | 1:30 pm

Future Projects

Chairs: Tony Cicinelli, Kiewit, Omaha, Nebraska, US, Leszek Glodkowski, Mott MacDonald, New York, New York, US

Sponsored by: The Walsh Group

SCMAGLEV – Innovative Mass Transportation in the Northeast Corridor (NEC)
Vojtech Gall, Gall Zeidler Consultants, Ashburn, Virginia US; Nikolaos Syrtariotis, Gall Zeidler Consultants, Ashburn, Virginia US; Timothy OBrien, Gall Zeidler Consultants, Ashburn, Virginia US; Ian Rainey, Northeast Maglev, Baltimore, Maryland US; Mark Berger, WSP, Washington, DC, District of Columbia US

The Northeast Corridor Superconducting Maglev Project (SCMAGLEV) entails construction of a high-speed train system between Washington, D.C. and New York City, with the first leg between Washington and Baltimore, MD. This innovative project will shorten travel times between Washington D.C. and Baltimore to approximately 15 minutes, and connect Washington, DC to New York City in under an hour. In 2021 the draft EIS is expected to be issued for comment with a Final EIS/ROD anticipated by early 2022. This paper provides an update on the project as presented in Gall et al. (2020) and discusses the economic and environmental benefits, preferred alignment alternative, preliminary staging and launching of the TBMs for construction, and preliminary station design.

Design Development of the BCRUA Phase 2 Raw Water Delivery System Project
James Parkes, Schnabel Engineering, Baltimore, Maryland US; Aaron Archer, Walker Partners, Austin, Texas US

This paper presents design considerations for the underground elements of the pending BCRUA Phase 2 Raw Water Delivery System Project. These elements include two lake taps; a 9,000-ft, minimum 10-ft OD intake tunnel; a suction chamber with 6 pump shafts with 72-inch casings; a 30-ft diameter, 300-ft deep shaft; a 2,600 LF transmission tunnel with 84-inch steel liner; and a 130-ft deep transmission riser shaft. The tunnels and shafts will be excavated through the Glen Rose limestone. The design development included consideration for technical requirements, easements, third party commitments, previous local project experience, and constructability considerations based on contractor outreach.

A New Era of Tunneling Planned for Houston – Going Deep to Solve Regional Water Supply, Wastewater, and Drainage Problems
Chris Mueller, Black & Veatch, Houston, Texas US; Todd Wanless, Black & Veatch, Kansas City, Missouri US; Sergio Flores, Black & Veatch, Houston, Texas US; Shannan Dunne, City of Houston, Houston, Texas US; Scott Elmer, Harris County Flood Control District, Houston, Texas US

Between 2010 and 2018, Houston added more than 1 Million residents; the third largest rate of growth in the nation. With growth, the region faces new challenges with water supply, capacity of its wastewater system, and regional drainage. While tunnel construction has been limited in Houston since the Clean Water Program of 1990’s, it is about to see a resurgence to improve water supply reliability and to reduce flood risks and sanitary sewer overflows. This paper examines the challenges with “going deep” below the built urban environment and related to high ground water; stiff, fissured clays; flowing silts and sands; faults; hazardous materials; and abandoned well fields.

Upgrading the Coal Creek Trunk Sewer
Joseph Clare, Tetra Tech, Seattle, Washington US; Ron Bard, Brown & Caldwell, Seattle, Washington US; Elizabeth Matson, King County Wastewater Treatment Division, Seattle, Washington US

It’s not the 60’s anymore. Upgrading wastewater pipelines in the current era demands the latest trenchless technology to minimize impacts. King County Wastewater Treatment Division in Seattle, Washington is designing a nearly mile long Direct Pipe® influent sewer combined with microtunneling to replace a 60’s era trunk sewer constructed along and within Coal Creek and its natural area. Direct Pipe® and trenchless installation was chosen due to the challenges of suburban neighborhoods, natural creek environment, topography, and geology. A collaborative effort between owner, designer, and construction manager provide the foundation for success.

Tunnel Design Aspects the New Haven Downtown Storm Sewer Infrastructure Improvement Project
Gregory Sanders, CDM Smith, Kansas City, Massachusetts US; Michael Schultz, CDM Smith Inc, Boston, Massachusetts US

The City of New Haven is proposing to construct Downtown Storm Sewer Infrastructure Improvement project to mitigate on-going stormwater flooding in the Long Wharf District. The proposed project includes a 200-cfs stormwater pump station; and a 914 meter (3,000 linear feet) long tunnel segment with an internal diameter of 2.1 meters (84-inch). The tunnel alignment will cross under the Long Warf railyard and then continue parallel to the US 34. This paper presents the local geology and subsurface conditions, as well as discusses the major project challenges and risks including construction in soft marine soils.


New and Innovative Technologies II

Chairs: Kaveh Talebi, Jay Dee Contractors, Livonia, Michigan, US, Soto Vardakos, WSP, New York, New York, US

Emerging Data Processing Technologies for TBM Projects – State of the Art and Outlook
Ulf Gwildis, CDM Smith, Bellevue, Washington US; Ulrich Maidl, MTC - Maidl Tunnelconsultants GmbH & Co. KG, Muenchen, Bavaria DE; Jamal Rostami, Colorado School of Mines, Golden, Colorado US

Automatically acquired machine data during TBM advance is typically processed by specialty software to offer the project team data visualization and evaluation options. Interfacing with GIS, CAD, 3-D geologic model, and instrumentation data bases allows Building Information Modeling (BIM) of the tunnel as-built condition. Application of Artificial Intelligence (AI) processes such as Machine Learning (ML) have already been used for hard rock TBM performance prediction and exhibited the potential of big data analytics. This paper outlines anticipated disruptive technological advances with implications on geotechnical exploration, TBM operation, face condition tracking, subsoil risk allocation, and claims management in the future.

Relevance of Continuous InSAR Monitoring and Trend Detection Analysis for Tunneling Projects
Cyriac Sebastian, TRE Altamira Inc., Vancouver, British Columbia CA; Giacomo Falorni, TRE Altamira Inc., Vancouver, British Columbia CA; Sara Del Conte, TRE Altamira Inc., Vancouver, British Columbia CA; Marie-Josée Banwell, TRE Altamira Inc., Vancouver, British Columbia CA

Satellite-based Interferometric Synthetic Aperture Radar (InSAR) is increasingly being recognized as a monitoring technique that complements other in-situ techniques in effectively detecting and measuring surface displacement. With the advancements in radar signal processing, a continuous InSAR update service is now possible, using every new satellite image that is acquired. This enables InSAR users to receive more frequent updates combined with trend variation analysis, providing crucial highlights of anomalous behavior. The paper focuses on project case studies where continuous InSAR monitoring has proved to be key in identifying displacement trend changes near tunnel alignments.

Quantification of Tangible and Intangible Benefits of Digitalization in Tunnel Construction
Jacob Grasmick, Maxwell GeoSystems, Golden, Colorado US; Angus Maxwell, Maxwell GeoSystems, Golden, Colorado US

As the tunneling industry continues to adopt Tunnel 4.0, digital twins of the tunnel construction site are becoming standard requirements for tunneling projects. However, the benefits of these remain unproven to many practitioners. The paper discusses the various implementations of digitalization and describes efforts to combine all data types to analyze the relationships between influences, predictions and performance in a single digital platform. This includes data pertaining to investigations, design, construction, monitoring and post-construction asset performance and management. Based on 16 years of global tunneling projects the paper aims to quantify the tangible and intangible benefits of such systems. Using a number of real examples, the paper describes where opportunities were taken and where they went unrealized. Challenges and considerations for both procuring and developing these digital twins are also discussed.

The Application of Artificial Intelligence (AI) at NEBT Project
Daniele Nebbia, The Lane Construction Corporation, Washington, District of Columbia US; Michael Mooney, Colorado School of Mines, Golden, Colorado US

For more than a decade the tunneling industry has explored the potential and benefits of macro synthetic fiber (MSF) reinforced concrete solutions for precast tunnel segments. Parallel to industry investigations, academic research is being undertaken to better understand this material when subjected to the typical loads expected during mechanized tunneling. This paper investigates the performance of MSF reinforced precast concrete tunnel segments by means of an experimental program comprising testing of full-scale tunnel segments. The presentation of the satisfactory results of the experimental testing programme will be complemented by brief case histories from successfully executed projects, including an America’s First.

Review of Measured Activity Times in Operation of an Open Type TBM and their Impacts on Machine Utilization
Ryan O'Connell, Colorado School of Mines, Golden, Colorado US; Jamal Rostami, Colorado School of Mines, Golden, Colorado US; Anuradha Khetwal, Colorado School of Mines, Golden, Colorado US

Tunnel boring machine (TBM) utilization is a critical factor for predicting machine performance. This study presents a preliminary analysis of the different activity time and downtime components from hard rock TBM projects at Stillwater mine, USA and another private project. A discrete event simulation software, Arena©, was used for the simulation of the TBM operation. The results of the simulation model were compared with the recorded activity times and downtimes of the projects. This work presents the sensitivity of the utilization factor to selected activities in the projects and the impact of geology and site set-up/logistics on machine performance.


Pressurized Face Tunneling

Chairs: Peter Raleigh, McMillen Jacobs Associates, Pasadena, California, US, Anton Hupfauf, Frontier Kemper

Calibration Techniques for Discrete Element Method Analysis in Soft Ground TBM Applications.
Glenn Mongillo, DynaMEK Group Ltd., Mississauga, Ontario CA

Discrete Element Method (DEM) software has been successfully used to simulate various machine / soil interactions and provide insight for industries such as mining and bulk material processing. This paper will investigate typical calibration techniques used in particle models for DEM simulation and physical calibration experiments with soft ground TBM cutting tools to incorporate parameters such as tool drag forces that contribute to required TBM torque. With a well calibrated DEM model, it is expected that TBM simulation results will be more meaningful and provide better insight into TBM performance, power requirements, cutting tool placement, and overall cuttinghead design.

TBM and Logistics for an Underground Island-to-Island Tunnel Project
Martha Gross, Virginia Department of Transportation, Norfolk, Virginia US; Alexandre Cochennec, Hampton Roads Connector Partners, Norfolk, Virginia US; Ruben Rubal, Dragados USA, New York, New York US; Sergio Estebanez, Hampton Roads Connector Partners, Norfolk, Virginia US; Yvonnick Rescamps, Hampton Roads Connector Partners, Norfolk, Virginia US

The HRBT Expansion project initiated by VDOT will add two 1.5-mile TBM bored tunnels to two existing immersed-tube tunnels between artificial islands, part of the connection between Norfolk and Hampton across the Chesapeake Bay in Virginia, USA. The new bored tunnels will be built by Hampton Roads Connector Partners (HRCP), a joint venture of Dragados USA, Vinci Construction, Flatiron Constructors and Dodin Campenon Bernard. This paper addresses the key features and functions of the TBM selected as well as of its ancillary equipment, including barging segments to and muck from an artificial island, to mitigate the risks on this project.

Management of the Water Inflows During Construction of the Three Rivers Protection & Overflow Reduction Tunnel (3RPORT)
Paolo Perazzelli, Pini Swiss Engineers, Zurich, Zurich CH; Roberto Schuerch, Pini Swiss Engineers, Zurich, Zurich CH; Miriam Piemontese, Pini Swiss Engineers, Zurich, Zurich CH; Emidio Tamburri, Lane-Salini Impregilo, Fort Wayne, Indiana US; Francesco Chiappalone, Lane-Salini Impregilo, Fort Wayne, Indiana US; Lance Waddell, Lane-Salini Impregilo, Fort Wayne, Indiana US

The Three Rivers Protection & Overflow Reduction Tunnel is part of the Long-Term Control Plan of the City of Fort Wayne, Indiana (USA). The 7.5 km, 4.87 m internal diameter tunnel is excavated through carbonate rocks by means of a slurry TBM. Due to the high hydraulic conductivity of the rock mass and the high in situ ground water pressure (up to 6.5 bar), the management of the water inflow during TBM advance and standstills represents the major challenge of the project. The paper outlines the hazards related to the large water inflows and discusses the experience gained during construction.

Tailskin Brushes Replacement Under Difficult Ground Conditions – 3RPORT Project
Francesco Chiappalone, LANE, Fort Wayne, Indiana US; Daniele Nebbia, LANE, Washington, District of Columbia US; Lance Waddell, LANE, Fort Wayne, Indiana US; Emidio Tamburri, LANE, Fort Wayne, Indiana US

As part of 3RPORT Project, a 5-mile tunnel is excavated in hard rock with groundwater pressure of 4.5–5.3bar and water inflows up to 10,000GPM by a 19feet slurry TBM in Fort Wayne, Indiana. Indication of tailskin brushes deterioration and need for inspection and eventual replacement are noticed during the drive. A PU-grouting campaign was performed to allow the brushes replacement. The paper describes the planning of the intervention, procedures and controls established to timely assess the presence of potential hazards. Also, the paper focuses on the experience gained during execution and lesson learnt that could have prevented the intervention.

Two-Component Backfill Grouting at the Three Rivers Protection and Overflow Reduction Tunnel: Above and Below Ground Challenges and Solutions
Cristina Gabriela Oñate Salazar, MAPEI Corporation, Naperville, Illinois US; Tanner Murt, MAPEI Corporation, Pittsburgh, Pennsylvania US; Francesco Chiappalone, LANE, Fort Wayne, Indiana US; Lance Waddell, LANE, Fort Wayne, Indiana US; Carola Wenzel, Herrenknecht Tunneling System, Fort Wayne, Indiana US

The 3RPORT project is a 5-mile-long, 16-foot-diameter tunnel excavated in hard rock by slurry TBM in Fort Wayne, Indiana. Two-component grouting can be separated into two core areas of operation: batching and underground operations. This paper addresses the challenges faced and solutions implemented in these fundamental areas. The effects of external factors and their impacts on mix design and batching of grout will be explored. Underground, challenges of monitoring parameters and ensuring a proper mix between the two-components will be discussed, focusing on the adopted technical solutions and considerations to be taken in the design stage of tailskin grout ports.


SEM Applications and Projects

Chairs: Mike Stolkin, J. F. Shea, Indianapolis, Indiana, US, Julio Martinez, J. F. Shea, West Caldwell, New Jersey, US

Sponsored by: HNTB

Tunneling Under Downtown Bellevue on Time and Under Budget
Mun Leong, McMillen Jacobs Associates, Kirkland, Washington US; Chintan Salvi, McMillen Jacobs Associates, Seattle, Washington US; Chad Frederick, Sound Transit, Seattle, Washington US; Archie Kollmorgen, Guy F Atkinson, Renton, Washington US; Jaroslav Hosek, Mott McDonald, Seattle, Washington US

Downtown Bellevue Tunnel (DBT) is part of Sound Transit’s $3.7 billion, 14-mile light rail transit system from downtown Seattle, across Lake Washington, to the cities of Mercer Island, Bellevue, and Redmond. The tunnel was the first Sound Transit East Link project and posed significant construction risk. This paper discusses implementation of design changes to the soft ground tunneling method, implementation of several technologies such as the use macro-synthetic fiber initial shotcrete lining, use of spray-applied waterproofing, and use of shotcrete for the final tunnel lining. These efforts allowed for significant time and cost savings to the project.

Tunnel Spitzenberg - Tunnel Drive Hits a Historic Quarry
Pafos Busch, BeMo Tunnelling, Austria, Innsbruck, Tyrol AT; Johannes Jaeger, BeMo Tunnelling GmbH, Innsbruck, Tirol AT; Martin Fischer, BeMo Tunnelling GmbH, Innsbruck, Tirol AT

The tunnel Spitzenberg is a 600 m (1,970 ft) long twin tube motorway tunnel on Germany`s autobahn A44 between Kassel and Eisenach. Since felxibility was considered to be very important in the continuously changing geological conditions NATM was chosen as construction method. When passing an old quarry with only 1,80 m (6 ft) of overburden the excavation works became extraordinarily challenging. The paper not only describes the special methods, like double side wall drifts and pipe umbrellas, applied in this zone but highlights also the cooperation between the parties involved which in combination made the project a joint success.

Construction of the Plymouth Tunnel by SEM Based on a Permanent Shotcrete Liner
Jean-Marc Wehrli, Traylor Bros., Inc., Forest Hills, Indiana US; Nick Tabor, Traylor Bros., Inc., Alexandria, Virginia US; Richard Taylor, Traylor Bros., Inc., Alexandria, Virginia US; Norbert Fuegenschuh, Beton- und Monierbau USA, Inc., Vienna, Virginia US

The Plymouth Tunnel, constructed using the Sequential Excavation Method, forms part of the 16-mile long route of the Purple Line Light Rail Project sponsored by the Maryland Transit Administration, is approximately 1,220 feet in length, with a shallow vertical alignment located beneath a residential area. Challenging mixed ground conditions include surficial soils, decomposed Saprolite, and highly weathered to fresh rock. This paper discusses the construction aspects highlighting items that went according to plan as well as items that were adapted or changed during construction to suit the conditions encountered as well as challenges faced during the installation of a spray-applied permanent concrete liner.

Application of Surrogate Modeling for SEM Tunneling Simulation
Haotian Zheng, Colorado School of Mines, Golden, Colorado US; Michael Mooney, Colorado School of Mines, Golden, Colorado US; Marte Gutierrez, Colorado School of Mines, Golden, Colorado US; Christophe Bragard, Traylor Brothers, Los Angeles, California US

The sequential excavation method (SEM) is one of the most complex tunneling approaches, usually featured with irregular excavation profile and multi-drift configuration. The evaluation of SEM design is commonly achieved by computational simulations either by finite element method (FEM) or finite difference method (FDM). Conventional 2D plane-strain numerical analysis is inadequate to capture the three-dimensional effects from multiple tunneling advances, whereas longer running time and highly expensive computational efforts required by three-dimensional step-by-step simulations hinder its application in probabilistic analysis and real-time prediction. This fuels the desire to harness surrogate modeling methods that use cheap “surrogates” to reliably represent the expensive, simulation-based model. This paper proposes a framework for applying surrogate-based approaches to evaluate SEM construction, which can both benefit the uncertainty analysis in the design stage and real-time calibration during the construction process. The performances of several surrogate modeling approaches were tested and compared. A variance-based global sensitivity analysis (GSA) was performed on surrogate models to quantify the impacts of geotechnical parameters on the deformation responses induced by SEM construction. The Regional Connector Crossover Cavern project constructed in Downtown Los Angeles was set as the benchmark problem to demonstrate the efficiency and reliability of the proposed procedure.

Construction of the Newell Creek Dam Inlet/Outlet Replacement Project
Shawna Von Stockhausen, Mott MacDonald, San Jose, California US; Isidro Rivera, City of Santa Cruz, Santa Cruz, California US; Idit Zarchi, AECOM, Oakland, California US; Koichi Shimomura, Obayashi, California US

The City of Santa Cruz Water Department is replacing the existing Newell Creek Dam (NCD) inlet/outlet works at Loch Lomond Reservoir in the San Lorenzo Valley as required by the California Division of Safety of Dams. The project is comprised of new inlet works (three new inlets that control and convey flows and an intake control building), a new outlet structure for energy dissipation and beneficial releases into Newell Creek, a new dam seepage collection and monitoring system, and new 48inch and 10inch outlet pipelines. Notable complex project components include the integration of the new outlet pipes to the new inlets to be constructed via marine works in the wet. This paper will discuss how the project configuration met the Owner’s objectives, the progress of construction to date and plans to complete the work, and the tools being used to manage the project and risks through construction which include ProjectWise Construction Management software, partnering, and a dispute resolution board.



Wednesday, June 16 | 8:30 am

Geotechnical Considerations

Chairs: Christopher Lynagh, McNally Tunneling Corp., Westlake, Ohio, US, Lisa Smiley, Jay Dee Contractors, Cleveland, Ohio, US

Sponsored by: HNTB

Pre-Excavation and Early Work Activities for the Long Baseline Neutrino Facility Far Site
Seth Pollak, Arup, New York, New York US; Josh Willhite, Fermi Research Alliance, LLC, Lead, South Dakota US; Ben Seling, Kiewit-Alberici Joint Venture, Lead, South Dakota US

The Long Baseline Neutrino Facility Far Site at the Sanford Underground Research Facility in Lead, South Dakota will house four large detector tanks located one mile underground. Construction of the supporting infrastructure required for this project is already underway including installation of the waste rock handling system and preliminary drill and blast excavation of supporting drifts and chambers. This presentation will discuss the project transition from pre-excavation activity into preparatory excavation leading to mass excavation of the neutrino detector caverns.

Challenges in Rebooting Geotechnical Investigations
Mala Ciancia, HNTB Corporation, New York, New York US

Planned tunnel projects with advanced geotechnical investigations are more frequently being suspended because of changes in funding, politics, or local priorities. Some of these projects are ultimately canceled, some decelerate and stall, some resume after a short pause, and some restart after being mothballed for several years. The restarted project often differs at least slightly from the predecessor project in terms of alignment and design concept. This paper describes approaches to evaluating the quality and completeness of previous geotechnical investigations for a re-activated project, considering technological advances as well as changes in regulatory requirements, contracting approach, and site conditions which may have taken place in the time since the project was suspended.

Laboratory Study of Clay Clogging Issues for EPB TBM Tunneling Applications
Wei Hu, WSP USA, Detroit, Michigan US; Jamal Rostami, Colorado School of Mines, Golden, Colorado US

Tunnel boring machine (TBM) utilization is a critical factor for predicting machine performance. This study presents a preliminary analysis of the different activity time and downtime components from hard rock TBM projects at Stillwater mine, USA and another private project. A discrete event simulation software, Arena©, was used for the simulation of the TBM operation. The results of the simulation model were compared with the recorded activity times and downtimes of the projects. This work presents the sensitivity of the utilization factor to selected activities in the projects and the impact of geology and site set-up/logistics on machine performance.

Abrasivity and Cutter Life Assessment for TBM Tunneling in Cobbles and Boulders
Steven Hunt, Black & Veatch, Las Vegas, Nevada US; Glen Frank, Lane Construction, Seattle, Washington US

Maximizing cutter life when tunneling in mixed face ground that includes cobbles and boulders requires 1) assessment of abrasivity and strength parameters for soil matrix and rock clasts, 2) methods of combining both, 3) proper selection of cutters and 4) modified TBM operation. This paper presents approaches for addressing these factors sufficiently to improve tunneling success in mixed ground with cobbles and boulders. Current laboratory abrasivity testing will be assessed along with equivalent quartz content correlations to soil matrix and rock clast abrasivity. New approaches to combining abrasivity testing of both the soil matrix and rock clasts for various cobble and boulder volume ratios will be suggested to estimate cutter life and intervention intervals.

Geotechnical Investigation and Tunnel Design for the Sister Grove Outfall Tunnels
Gregory Sanders, CDM Smith, Kansas City, Massachusetts US; Micheal Schultz, CDM Smith Inc, Boston, Massachusetts US

In 2017, the North Texas Municipal Water District (NTMWD) initiated the design of the Sister Grove Regional Water Resource Recovery Facility (SGRWRRF) to provide additional treatment capacity for future population growth within the Lavon Lake watershed. To provide a discharge location for SGRWRRF approximately 4.5 miles of 2.4 meter (96-inch) internal diameter pipeline will be constructed, including 2.3-kilometer (7800) feet and 487 meter (1600 foot) long tunnel segments. This paper will discuss the anticipated geology of the two tunnel segments, selection of the tunnel alignment, the anticipated initial tunnel support requirements and other aspects of the project design.

Case Study- Innovatively Launching a Full-size TBM in Challenging Ground
Mahmood Khwaja, CDM Smith, Waban, Massachusetts US; Bernard Catalano, Bessac, Canonsburg, Pennsylvania US; Michael Schultz, CDM Smith, Boston, Massachusetts US; Janice McGovern, Suffolk County Department of Public Works, Yaphank, New York US

Launching a full-size pressurized-face Tunnel Boring Machine in difficult ground conditions is always challenging. Recently, few projects have innovated the process by scaling the trenchless method of pipe jacking to facilitate the launching of a full-size TBM without the need for large and deep trenches; starter/tail tunnels; or for incrementally installing supporting gear as the machine advances. This paper presents two such projects; evaluates the post-bid contractor proposed modifications; details the innovative use of pre-cast pipe segments to facilitate machine launch; and, provides an overall assessment of the benefits, challenges and lessons learned related to the modified approach.

Microtunneling & Trenchless Tunneling

Chairs: Stephen Price, Walsh, Little Falls, New Jersey, US, David Watson, Mott MacDonald, New York, New York, US

Robotic Mining and Micro Tunneling using Hypersonic Projectile Impact Technology Field Trial Results, Technical Evaluation and Economic Valuation.
Mark Russell, HyperSciences, Inc., Spokane, Washington US; Robert Urselmann, Aotea ltd., Cowan Bridge, Lancashire GB; Desiree Bernhard, HyperSciences, Inc., Spokane, Washington US; Brooke Colburn, HyperSciences, Inc., Spokane, Washington US; Charles T. Russell, HyperSciences, Inc., Spokane, Washington US; Kaito Durkee, HyperSciences, Inc., Spokane, Washington US

Hypersonic tunnel boring (HTB) uses directed, high velocity projectile impacts to remove rock. HTB is independent of rock strength and targets hard, abrasive rock and variable rock environments. This paper discusses history, theory and presents test (2x2m and .75x.5m tunnels) field trial results and technical and economic evaluation. The HTB tests are compared against the historic ‘project REAM’ and the concept against tunnel boring machines and drill & blast in design studies for full-scale 12m and 4.5x5.5m tunnels. The positive results indicate that under these conditions HTB can replace Drill & Blast and Tunnel Boring Machines.

The Role of Small Diameter Tunneling for Pipeline Installations
Peter Schmaeh, Herrenknecht AG, Schwanau-Allmannsweier, Baden-Wurttemberg DE

Nowadays, small diameter tunnels are increasingly considered in pipeline projects as an alternative for sensitive crossings or when soil conditions limit the use of conventional pipeline installation methods like HDD. Safety concerns play a key role, especially for inner-city installations. Pipe jacked microtunnels and small segment lining tunnels can serve as casing tunnels if access is required, e.g. during construction for the change of cutting tools in challenging ground conditions or for maintenance of the pipeline in operation. Small diameter tunneling solutions offer a high degree of flexibility for alignment design in terms of geology, length and radius.

Challenges to Tunneling in Abrasive Alluvial Material Above the Water Table using a SMTBM and an EPBTBM
Donald Arthur, Frontier-Kemper Constructors, Inc., Sylamr, California US; Rosmar Gonzalez-Sanchez, Frontier-Kemper Constructors, Inc., Sylamr, California US

Infrastructures continue to age and drinking water supplies are becoming scarce in the San Fernando Valley of Los Angeles, California (LA). Frontier-Kemper Constructors, Inc. (FKCI) was engaged by Los Angeles Department of Water and Power (LADWP) to complete the River Supply Conduit Improvement Upper Reach – Unit 7 (RSC7) Project. Two tunnel sections were bored using an 8.66-foot diameter Slurry Microtunnel Boring Machine (SMTBM) and a 13.50-foot diameter Earth Pressure Balance Tunnel Boring Machine (EPBTBM) to excavate approximately 12,150-linear feet (2.3 miles) of tunnels through highly abrasive late-Pleistocene-age Quaternary alluvial deposits (Old Alluvium) above the water table. The paper will discuss the challenges managing the TBM’s equipment degradation, use of soil conditioners, torque and advance rate while maintaining the necessary face pressures and parameters to limit over excavation and ground settlement.

Crossing an Environmentally Sensitive Shore Area - Micro-tunneling in the Australian Outback
Taner AYDOGMUS, Flatiron Constructors, Inc., Broomfield, Colorado US

The A$29 billion Chevron-operated Wheatstone Project is one of Australia’s largest resource projects. Located at Ashburton North, 12 kilometers west of Onslow in Western Australia, the project will consist of two LNG trains with a combined capacity of 8.9 million tons per annum and a domestic gas plant. The LNG Plant will serve the offshore gas fields, which are situated some 250 km off the coast of Onslow in Western Australia. Once operational and on-stream, the Wheatstone Project will contribute to Australia becoming the world’s second largest exporter of LNG. For crossing the environmentally sensitive shore area a micro-tunnel with an internal diameter of 2 m and approx. 1,242 m in length has been constructed by means of the pipe-jacking method. The micro-tunnel will accommodate a 1.1 m diameter pipeline (trunkline) to deliver gas from the offshore fields LNG Plant. The Wheatstone shore crossing design involves a number of unique challenges owing to its coastal location, where the alignment crosses through a shore area and terminates in a marine environment. This paper provides an overview of the Wheatstone Shore Crossing Project, presents the key features, and discusses the main aspects of the micro-tunneling design.

Lessons Learned at the Trampas Dam
Todd Kilduff, Kilduff Underground Engineering, Inc., Denver, Colorado US; Paul Wilkinson, Kilduff Underground Engineering, Inc., Denver, Colorado US

A Contractor advanced a 60-inch diameter, microtunnel below an earth embankment dam in California. The project was confronted with several challenges that required immediate hands on solutions.


Project Planning and Risk Management

Chairs: Mohamed Younis, Surface and Tunneling Engineering, Frederick, Maryland, US, Keith Ward, Seattle Public Utilities, Seattle, Washington, US

Sponsored by: HNTB

Toledo Waterways Initiative – Completion of an 18-Year LTCP Program
Leo Gentile, Black & Veatch Corporation, Indianapolis, Indiana US; Julie Cousino, City of Toledo, Toledo, Ohio US

The $528 million Toledo Waterways Initiative (TWI) was implemented by the City of Toledo in 2002, completed in June 2020 and consists of three storage and conveyance tunnels, three 14 to 18 million gallon below-grade storage basins, miles of sewer separation and interceptor improvements to dramatically reduce combined sewer overflows to the Maumee River, Ottawa River and Swan Creek. All flow into Lake Erie. The City’s 150-year history as a Midwest shipping, manufacturing and transportation hub provided design engineers and contractors no shortage of unknown underground challenges to complete the projects.

Tunnel Vision: Planning a Resilient 21st Century Wastewater System for Houston
Brian Gettinger, Freese and Nichols, Houston, Texas US; Jack Canfield, Houston Public Works, Houston, Texas US; Fazle Rabbi, Houston Public Works, Houston, Texas US; Shannon Dunne, Houston Public Works, Houston, Texas US; Chuck Wolf, Freese and Nichols, Houston, Texas US; Richard Weatherly, Freese and Nichols, Pearland, Texas US

During Hurricane Harvey over 60% of the 39 WWTPs, including the low-lying 25 MGD Sims North WWTP, and one third of the 382 lift stations owned and operated by the City of Houston were flooded resulting in extensive facility damage, loss of service and uncontrolled release of untreated wastewater into bayous and creeks. In response the City has embarked on an effort to improve system resiliency by consolidating at-risk facilities with a network of deep sewer tunnels to augment the capacity of the existing 6,000 miles of sewer mains. Investigations on the cost to mitigate the flood damages by raising the plant at Sims North WWTP is estimated at nearly $450 million. Instead of spending $450 million to raise the plant, the funds will be directed to eliminating Sims North WWTP, along with the Scott Wet Weather Facility and providing a more robust and resilient wastewater system for the Sims basin area of Houston. The backbone of this new system is a 4.5-mile-long, 110 inch diameter deep gravity sewer tunnel that will convert a system heavily reliant on distributed lift stations to a majority gravity system with a deep consolidated lift station at the WWTP.

Methodologies for Sound Transit’s Proposed New Tunnels for LINK Light Rail Expansion
Matthew Preedy, Sound Transit, Seattle, Washington US; Dirk Bakker, Sound Transit, Seattle, Washington US; Anthony Pooley, Sound Transit, Seattle, Washington US; Mike Wongkaew, HNTB, Seattle, Washington US; Jerry Dorn, HNTB, Seattle, Washington US; Raghu Bhargava, HNTB, Seattle, Washington US

Sound Transit will add 62 miles of light rail to the Puget Sound area, including connections to the neighborhoods of West Seattle by 2030 and Ballard by 2035. These connections include considerations for both elevated and tunnel alternatives, as well as a new downtown tunnel for which different configurations are being considered with potentially very different construction logistics and risk profiles. This paper describes the latest developments in the ongoing evaluation process that will inform the consideration of different tunnel and station construction methods, technical and operational challenges and contracting methodologies, including construction of deep stations in dense urban environments.

Back on Track: The Downtown Rail Extension
Derek Penrice, Mott MacDonald, Pleasanton, California US

The Downtown Rail Extension (DTX) is a regionally critical project, extending Caltrain commuter and future high speed rail service from its northern terminus at the 4th and King Station via a 1.3-mile tunnel to the completed Salesforce Transit Center in downtown San Francisco. Studied since the 1970’s, DTX’s EIS/EIR has been approved, and key stakeholders are aligned on the projects configuration and its expedited delivery. The paper describes efforts to optimize the DTX configuration, to develop an informed project delivery strategy which incorporates construction industry feedback on project phasing, contract packaging and procurement methods that accomplishes the projects budget goals.

Contracting Practices for Underground Freight Transportation Projects: A Look at Cargo sous terrain
Juerg Kuenzle, Office for Construction Dispute Resolution, Bern 8, Bern CH

Underground freight transportation (UFT) projects are large and complex long-term multi-billion undertakings. UFT projects involve multiple parties who perform different types of services and works under multiple contracts, which form a system of interrelated bilateral contracts. Specific contracting practices are needed to build a coherent and sustainable structure of commitments and responsibilities across the system boundaries of individual contracts. This paper describes and proposes elaborate contracting practices designed to overcome the characteristic challenges of UFT projects, including those relating to the various interfaces and interdependencies between services and works under multiple contracts. This paper considers the example of Cargo sous terrain (CST), a privately funded underground logistics system in Switzerland. The first phase of this project consists of a 70-kilometer underground section connecting ten large access shafts, so-called “hubs”.


Tunnel Rehabilitation

Chairs: Renee Fippin, McMillen Jacobs Associates, San Francisco, California, US, Ben McQueen, Frontier Kemper

North Auckland Line – Tunnel Refurbishment
Harry Asche, Aurecon, Indooroopilly, Queensland AU; Shu Fan Chau, Aurecon, Newmarket, Auckland NZ

The North Auckland Line, in New Zealand, is being upgraded to pass Hi-Cube containers. The line includes many tunnels and bridges which need to be refurbished to improve structural clearances. One of the tunnels along the line, the Makaru Tunnel, has posed special challenges. Opened in 1898, the tunnel suffered multiple collapses during construction, has shown significant distortion during operation, and has been repaired many times since opening. Successfully enlarging this delicate and distressed structure has involved historical research, advanced analysis and design, and careful construction. The results provide lessons for dealing with brick lined tunnels and poor ground conditions.

Rehabilitation of an 1880s Limestone Block Tunnel below an Active Railroad Corridor
Joseph Welna, Barr Engineering Co., Minneapolis, Minnesota US; Jim Herbert, Barr Engineering Co., Minneapolis, Minnesota US; Nathan Campeau, Barr Engineering Co., Minneapolis, Minnesota US

Constructed by stonemasons over 120 years ago, the Trout Brook storm sewer was in need of rehabilitation. A routine inspection of the 10-ft. limestone block tunnel revealed degraded and missing mortar between the blocks allowing significant infiltration and soil migration through the tunnel joints. Conditions including damaged and missing blocks were considerably worse in a 250-ft long segment beneath a busy mainline railroad corridor. Barr’s solution included tuck-pointing to repair the mortar joints, shotcrete overlay, and construction of a hybrid cast-in-place/shotcrete “tunnel within a tunnel” to support the mainline railroad loads.

Upgrading Mount Royal Tunnel to Latest Standards
Behrouz Esmaeilkhanian, AECOM - Consultants Inc. Canada, Montreal, Quebec CA; Mohammad Motallebi, AECOM - Consultants Inc. Canada, Montreal, Quebec CA; Verya Nasri, AECOM, New York, New York US

The Mont Royal Tunnel (MRT) is a 100-year-old railway tunnel located in Montreal, Canada. The tunnel is approximately 5 km long, 9.6 m wide and 4.4 m high, with a constant 0.6% grade. This existing tunnel will be used by the new Montreal light rail transit network, Réseau Express Métropolitain (REM). This requires the tunnel to be inspected, rehabilitated and made compliant to the recent safety standards. This paper presents the details of the structural inspection and rehabilitation of the tunnel along with the repair methods, addition of a center wall as well as the enlargement of the tunnel section.

Accelerated Rehabilitation of the White Rock Tunnel
David Jurich, Mott MacDonald, Lakewood, Colorado US; Nathan Bowersox, Sacarmento Municipal Utility District, Sacramento, California US; Zuzana Skovajsova, COWI North Ameria Inc., Florham Park, New Jersey US; Brian Harris, Drill Tech Drilling and Shoring, Antioch, California US

When unwatered after nearly 60 years of operation, the White Rock Tunnel of the Upper American River Project in the foothills of the Sierra Mountains exhibited failing rockbolts and ground falls. Repairs designed for the 5 mile-long, 24-foot horseshoe unlined hydropower tunnel included pattern rock bolts, shotcrete, and cleanout of the rock trap. The work, originally scheduled for two 3-month winter outages, was completed under challenging conditions in a single 4-month outage following a carefully sequenced work plan using robotic shotcrete and rockbolter machines. Flexibility, creative solutions, and collaboration by all parties were key to project success.

Verification and Update on High Pressure Concrete Plug Leakage Remediation
Seung Han Kim, AECOM, Oakland, California US; Jay Lin, AECOM, Oakland, California US; Carlos Jaramillo, Marsh Wagner, San Francisco, California US; Jeremy Yager, PG&E, San Francisco, California US; Bob McManus, PG&E, San Francisco, California US; Andrew Yu, PG&E, San Francisco, California US

The concrete plug separating the pressure tunnels from the open-air tunnels has leaked since the first filling at the Helms Pumped Storage Plant located in California. A grouting program was successfully implemented in 2009 to reduce the leakage from 1,000 gpm to 25 gpm. Recent observations indicated increasing water leakage through new pathways, leading to a decision to execute a high-pressure grouting and waterproof membrane installation program in 2017. The grouting and membrane installation program was successfully executed in the areas adjacent to the plug and the largest hydraulic gradients are suspected to present.

Best Practice for Comprehensive Condition Assessments of Remote Tunnels
Dani Delaoye, Mott MacDonald, Vancouver, British Columbia CA; Herman Gill, Mott MacDonald, Vancouver, British Columbia CA; Madelyn Rubin, San Francisco Public Utilities Commission, Moccasin, California US

The Foothill Tunnel is a remote 16-mile-long untreated drinking water tunnel in the San Francisco Public Utilities Commission’s (SFPUC) Hetch Hetchy Water and Power system. The 14-foot horseshoe shaped tunnel, constructed in the 1920s, is lined intermittently with concrete over approximately 53% of its length, with the balance being unlined rock. After detailed planning, in January of 2020 Mott MacDonald and SFPUC staff completed a visual inspection and documented the condition of the tunnel with electronic data collection, photographs, and video with audio recording. The result was a comprehensive condition assessment that identified key areas of the tunnel to monitor.


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