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By Dan Preston, Shane Yanagisawa, Robert Marshall, Don Deere

Geotechnical Baseline Reports often estimate the number of cobbles that will be encountered in terms of volume or weight. These estimates are practically impossible to verify in the field. ClaroVia Holdings in conjunction with Frontier Kemper Constructors Inc. developed Digital Geologist 2.0 to classify and count cobbles discharged from an EPB TBM at the RSC7 project in Burbank, CA. The system worked by using two stereoscopic laser sensors with a global shutter to scan and count cobbles at 12 frames per second. Results of the effort are revealed along with lessons learned and paths for improvement.

Jun 13, 2023

By Drew Bazil, David Smith, Matteo Ferrucci, David Pittman

The Gateway program will provide additional rail capacity between New Jersey and Manhattan. This paper describes how a 70-foot-deep section of cut and cover tunnel was designed to directly support future high-rise towers. The tunnel will link previously completed tunnel sections under Hudson Yards to future tunnels under the Hudson River. The design aims to minimize constraints on future overbuild and future tunnels, while maximizing constructability within a small worksite. The tunnel will pass under the High Line elevated walkway, next to an active rail yard, and close to a subway tunnel. The design was developed by a tri-venture of WSP, STV and AECOM. WSP led the design of major underground works; STV designed utility relocations and the underpinning concept for the High Line; and AECOM designed temporary in-tunnel systems. Construction is expected to start in 2023.

Jun 13, 2023

By Sean Peterfreund, Grant Finn, Ty Jahn

For urban underground development involving tieback anchors for excavation support, authorities having jurisdiction typically require tiebacks to be de-tensioned before project completion. This paper updates “A Proactive Approach to Tieback Anchor De-tensioning” (by Peterfreund and Finn, published in the 2017 RETC Proceedings), which discussed a new method employed in a cut-and-cover transit station project. Since publication of that paper, 237 tiebacks were successfully and rapidly detensioned from using a small-diameter drill to cut strands from the surface. To the authors’ knowledge, this was the first intentional large-scale use of a drilling method for this purpose.

Jun 13, 2023

By Alfredo Valdivia, Dominic Reda, Vojtech Gall

The design and planning for the construction of a new passageway to improve access and circulation to better accommodate anticipated increased passenger flow within Grand Central—42nd Street Station. The passageway includes the break-in of an over 100-year-old station cavern with an innovative design implementing a protective structure above the existing track to allow for safe train operations and passenger circulation during construction. Construction of the new passageway follows the Sequential Excavation Method. This paper will present the innovative solutions that went into the preliminary design and planning considering construction access, site logistics, risk management, structural retrofitting, instrumentation and monitoring, and impact assessments.

Jun 13, 2023

By Connor Langford, Murray Gant, Ken Massé

For public organizations, preparing accurate project cost estimates is a critical component in capital project planning. Project delivery methods provide a structured approach to moving projects through the design and construction lifecycle, and typically use cost estimates as key inputs at each stage to determine if the project will advance. As design stages can occur years or even decades before construction contracts are awarded, estimates need to make reasonable assumptions about how the work may be executed (means and methods) as well as potential future market trends so that appropriate values for material pricing, labour costs, escalation, and owner’s costs can be included. This process is challenging enough during stable markets, as historic trends can often be misleading and require a suitable understanding of economic factors to use appropriately. When you mix in the market volatility that has been observed since 2020, developing accurate project cost estimates becomes even more challenging. In cases such as this, having a structured approach to cost estimating that includes an adequate risk-based reserves cannot be overstated as it provides the basis for ongoing project decisions. This paper explores some of the historic and more recent market trends that have impacted key aspects of project cost estimates for capital project planning. It also provides recommendations on how to develop cost estimates for infrastructure projects, with examples from Metro Vancouver, which plans for and delivers regional-scale services to 2.6 million residents. A brief commentary on the use of escalation clauses in contracts is also presented.

Jun 13, 2023

By Todd Kilduff, Ryan O’Connell

Pipe canopies continue to gain momentum as a reliable methodology for construction of excavations below critical facilities with minimal surface settlement tolerances, such as railroads or roadways. Two tunnel projects designed by Kilduff Underground Engineering in the Salt Lake City, UT area, each at varying stages of completion, had project design criteria for selection of a tunneling methodology to minimize surface settlement. Both projects consist of a pedestrian tunnel, one crossing beneath a major roadway in downtown Salt Lake City and the second beneath UPRR tracks. Both projects were in difficult, coarse alluvium/fan ground conditions with project criteria that resulted in minimal cover above the tunnel. For each project, a pre-support pipe canopy was designed, requiring the placement of steel, canopy pipes driven the extent of the tunnel length. The pipe canopy is installed using a trenchless technology and then excavated with SEM tunneling and shoring provided by traditional support of excavation methods. The pipe canopy pre-support method offers a low-impact method to install an underpass beneath critical structures by adding significant stiffness to the subgrade to mitigate surface settlement during the main tunnel excavation sequence. These case studies seek to communicate the challenges associated with pipe canopy installation in site-specific ground conditions and explains how these challenges were overcome. This paper aims to define the project risks and describes the pipe canopy methodology as a viable solution to mitigate surface settlement in low cover tunneling scenarios.

Jun 13, 2023

By Paul Taurasi, Mahmood Khwaja, Anjuli Corcovelos, William Brick

California’s San Diego County Water Authority provides a safe and reliable water supply to more than 3.3 million residents through twenty-four member agencies. The 2nd Aqueduct pipelines, a critical infrastructure consisting of three large-diameter pipelines, are susceptible to natural threats including streambed erosion, channel migration, and seismic hazards within the 3,840-foot-long Moosa Canyon segment of the alignment. A state-of-good repair, hazard mitigation, and resiliency project is progressing to ensure uninterrupted water supply. For each pipeline, a segment will be replaced by tunneling. A high-level project development approach is presented, focusing on alternative selection, environmental and geotechnical considerations, and operations and maintenance constraints.

Jun 13, 2023

By Rafael C. Castro, Paul V. Savard, Kathleen M. Murtagh

Preliminary design is underway for the Massachusetts Water Resources Authority’s (MWRA) next major tunnel program, the Metropolitan Water Tunnel Program (MWTP). The MWTP is the latest part of MWRA’s ongoing efforts to achieve redundancy for its metropolitan water transmission system including its historic deep rock City Tunnel, City Tunnel Extension and Dorchester Tunnels. The MWTP comprises several deep rock tunnels that will be approximately 10-foot to 12-foot finished diameter totaling just over fourteen miles long and ten connections to existing large diameter surface piping and pumping stations. This paper will present an update on current engineering and permitting efforts, packaging schemes, and the schedule to complete the MWTP.

Jun 13, 2023

By R. Schuerch, C. Cimiotti, M. Piemontese, N. Karlin, P. Perazzelli, P. Halton

The new Los Angeles, California JWPCP effluent outfall tunnel will transport secondary-treated effluent from the Joint Water Pollution Control Plant in Carson to White Point Manifold. The tunnel will be approximately 7 miles (11 km) long with a finished internal diameter of 18 ft (5.5 m). The TBM is designed to cope with high water pressure up to 10 bar. The geotechnical challenges are due to the heterogeneous subsurface conditions: in the first half of the alignment, the tunnel runs through soils with a low overburden under urban areas, and, in the second half, the tunnel runs through extremely weak, intensely faulted rock masses with high overburden. Following an overview of the project, this paper focuses on the northern portion of the alignment and presents a decision-making procedure developed during pre-excavation phase in order to cope with the expected heterogeneous conditions during mining. The risk assessment and the TBM operational design of the southern portion will be dealt with in a future paper.

Jun 13, 2023

By Cory Bolen, Nadav Bar-Yaakov, Eric Zimmerman, Gregory Raines

The Chimney Hollow Reservoir Project broke ground in August 2021, constructing the tallest Asphalt Core Dam in North America, intending to improve reliability of drinking water supply to Northern Colorado communities. Aiming to expedite and streamline the geological mapping process in the tunnel, Stantec’s teams have developed a mobile and web-based GIS application for digital mapping input and rock mass evaluation, allowing real time decision making for assigning tunnel support class and resulting in a faster more efficient process. The following article presents and demonstrates the GIS mobile and web application-based process, the mapping results and review additional uses of the database created.

Jun 13, 2023

By Raphael Victor

The construction and modification of tunnels brings a requirement for precise measurement of convergence and divergence to safeguard the structure, maintain safety and provide the assurance needed to maintain efficient progress. Established methods include manual measurement using tape extensometers and automated methods using photogrammetry and automated total stations. Drawbacks include the need for frequent access, power supply, cabling, and cost. The paper describes how the development of reliable optical displacement sensors (ODS) has changed the landscape. ODS sensors are connected to a long-range wireless mesh communications network via a solar-powered gateway outside the tunnel, with data instantly transmitted to the internet. A sensor and its reflector target can be installed in 20 minutes and is maintenance free for a decade. Tunnel movement is measured to sub-millimeter precision with repeatability of ±0.15 mm. Integration of a triaxial tilt sensor allows slope distance to be converted to horizontal and vertical changes and allows rotational movement to be determined. Applications include new-build and long-term structural health monitoring. Case studies will be given, including the refurbishment of rail tunnels in Spain where the ODS measured movement during track lowering in a situation where no other automated system was considered viable.

Jun 13, 2023

By Robin Dill, Julian Prada, Kathryn Kelly, Brian Hann, Todd Moline

Narragansett Bay Commission’s (NBC) Pawtucket Tunnel Project includes construction of the 11,600-ft long, 30-ft ID, deep rock tunnel. This paper presents insight into the features and benefits of lump-sum, design-build that led NBC to select it as the project delivery method. The use of a design-build contracting process that included proprietary meetings to discuss and obtain feedback on Alternative Technical Concepts as well as to facilitate reaching consensus on modifications to the GBR-B is also described. The discussion includes features and benefits of design-build process that not only addressed NBC’s desired outcomes, but also allowed the Design-Builder to propose several innovative changes to the Base Technical Concepts included in the bid documents, and to develop a GBR-C that was compatible with their proposed means and methods of construction and addressed what they believed to be the more significant subsurface risks on the project.

Jun 13, 2023

By Karin Bäppler

Hydropower produces almost two-thirds of the world’s renewable electricity generation and delivers a major contribution on the ambition of the Paris Agreement and Sustainable Development Goals (SDG) with a range of benefits to society and environment. These include clean and flexible generation and storage in addition to reduced dependence on fossil fuels and avoidance of pollutants. The Limberg III PSP is one of the European projects that addresses the implementation of the UN SDGs. The challenge of the project is the construction of a 770 m long pressure shaft to be excavated with a TBM at an inclination of 42°.

Jun 13, 2023

By Nik Sokol, Eric Sekulski, Leo Weiman-Benitez, Jon Hurt, Shrinidhi Vijayakumar, Phaidra Campbell

The Silicon Valley Clean Water (SVCW) Gravity Pipeline (GP) is the first Progressive Design Build (PDB) tunnel completed in North America. As part of the Regional Environmental Sewer Conveyance Upgrade (RESCU) Program, the tunnel is a key component to replacing and rehabilitating components of the existing conveyance system in San Mateo County, California. The GP consists of a large diameter Fiberglass Reinforced Polymer Mortar (FRPM) pipe installed inside a 4.1 m (13.5 ft) inside diameter, 5.3 km (3.3 mile) long precast concrete segmentally lined tunnel. The tunnel was constructed using a 4.6 m (15.2 ft) diameter Earth Pressure Balance (EPB) Tunnel Boring Machine (TBM) through heterogenous silts, clays and sands. Construction included two separate TBMlaunches from a centrally located access shaft, and a tunnel alignment below but in close proximity to very soft Young Bay Mud. Settlement criteria and mitigation strategies focused on protection of an existing 1.42 m (56 inch) diameter force main and adjoining structures along the alignment. This paper discusses the results of the theoretical settlement analysis versus the actual observed ground movements, while also presenting mitigation measures and adjustments made during tunneling to reduce the risks of adverse settlement.

Jun 13, 2023

By Denis Tepavac, Mark Trim

Structural performance of fiber reinforced concrete (FRC) depends on its ability to carry tensile forces after cracking. Australian Standards AS5100-2017 and AS3600-2018 are the only available design standards that establish a test procedure to determine strength and toughness of an FRC in direct tension. Direct tensile testing of fiber reinforced shotcrete samples was performed to determine if the model and guidelines in AS5100/3600 were applicable to shotcrete; all previous testing was from cast samples. In addition to direct testing, micro CT-scanning was also performed. The paper presents tests performed, results, and how the tests could be used on future projects. In addition, a brief summary is provided of the guiding structural mechanics used for estimating residual tensile strength and test methods utilized to verify those estimates.

Jun 13, 2023

By Jorge Ferrero, Andreas Raedle, Uhland Konrad, Michael Dutton, Keivan Pak Iman, Walter Trisi

Strabag, in partnership with Arup, is constructing the Advance Tunnel for the Scarborough Subway Extension (ATSSE); a project by Metrolinx and Infrastructure Ontario (Sponsors). The 10.7 m internal diameter single bore tunnel represents a significant departure from the traditional arrangement of twin subway tunnels in North America. ATSSE is the first-time steel fibers are used to solely reinforce a tunnel of this size in Eastern Canada. This paper discusses the challenges with design and acceptance of SFRC segments and the state-of-the-art numerical models employed to check the joint performance. The advance procurement approach for TBM and PCTL’s procurement to accelerate the project schedule is also presented.

Jun 13, 2023

By Enrico Pavese, Tim Kearney, Stefan Lemke

Watertightness is of central importance in hydraulic and underground structures but has always been associated with a risk, as demonstrated by the very high impact that water inflows have on the damage of linings and infrastructure (Howard, 1991; Sandrone and Labiouse, 2011). Concrete is vulnerable to groundwater and chemical contaminants in the soil. These can leach into the pores and cracks of the concrete and degrade its integrity, causing spalling and corroding the reinforcing steel. Moisture migrating into the building can also degrade structural elements over time and lead to mold and other hazards to occupants’ health. In this connection, the demands placed on the setup and detailed design of the seal depending on the negative influence by water on the one hand and on the other hand on the function of a construction in view to its watertightness classification. Thus, the reliable functioning of a seal is of particular significance in the case of traffic tunnels, which are not easily accessible for all subsequent repairs after the construction in seepage water and especially when located in a pressure water zone (risk–cost assessment). Requirements for the long-term efficiency and quality of underground structures have increased in recent decades. Today, the standard lifetime requirement for an underground infrastructure project is 100 to 120 years and, in some cases, even higher. This calls for high increased attention to the durability of the whole structure and of each individual element. Standards, which started as application guidelines given by the manufacturers, are available in the market since the 1980s and are constantly adapted to the current developments in various technical committees. Differentiations are made between: Manufactures application guidelines, case studies or published articles Test standards for the laboratory to guideline the testing procedures (air temperature, type of test equipment, dimensions, test speed, test duration, concentration, type of liquids, monitoring, tolerances, interpretation of results, documentation, etc.), developed by committees based on material and laboratory experts Application standards, which include test standards but also the related minimum performance requirements (values) for material, processing, and quality assurance (practical tolerances), developed by committees based on a wide range of experts (e.g., designers, construction companies, applicators, manufactures, owners, test institutes, quality engineers) and therefore also based on a wide field of experience, different views and up-dated case studies. In the following there are some examples of guidelines and published information’s, ranked according to the year of issue, which are relevant for the development of waterproofing specifications in the tunnel industry:

Jun 13, 2023

By Diana Diaz, Rakshith Shetty, Vitaly Proschenko, Mike Mooney

Cohesive clay soil poses a significant risk to earth pressure balance tunnel boring machines (EPBM) due to unstable face pressure, clogging potential, high cutterhead torque, poor muck flow, low advance rate, etc. This paper details the performance measures desired when EPBM tunneling in clay soil, and the scientifically-supported conditioning methods to transform in-situ clay to a muck with such characteristics, giving particular attention to ground conditions. The paper then examines TBM data from multiple clay soil projects in the context of these performance measures to demonstrate the influence of cohesive soil conditioning on EPBM performance.

Jun 13, 2023

By Laurent Rus, Bakar Amara, Jean Habimana

The La Fontaine Tunnel in Montreal, Quebec is currently undergoing major structural rehabilitation work and systems upgrade work to comply with current codes, standards and best practices in fire life safety and to extend its lifespan of this 55-year-old immersed tube tunnel for at least another 40 years. The paper discusses design consideration of ongoing works that include structural analyses to evaluate repair strategies for the post-tensioned reinforced caissons, the scheme to repair two leaky joints between caissons, the design of passive fire protection that involved in situ and real scale laboratory tests, and other tunnel systems upgrades.

Jun 13, 2023

By Dan Ifrim, Andre Solecki

Tunneling could be a major challenge to tunneling contractors as tunneling operations can be seriously affected by the Tunnel Boring Machine (TBM) performance. Specifying the appropriate TBM methodology, selection of systems and features, is critical for managing tunnel risks and contribute to successful tunneling project. The paper analyzes tunneling records from the recently completed City of Toronto’s Ashbridges Bay Treatment Outfall tunnel project and underlines the righteous selection of the TBM type and associated TBM systems in achieving good advance rates during tunnelling and managing project risks. The paper intends to draw attention of a few aspects of TBM technical specification importance and highlight the lessons learned from this process.

Jun 13, 2023