A Look at How HMM Is Helping Transform Tunnel Engineering and Construction
The field of tunnel engineering and construction is constantly evolving. While basic tunneling methods may be the same, and Mother Nature is still the boss, technological advances are making construction more efficient, precise and with greater risk avoidance than in years past.
In this article, we take a look at technological innovations and how they are being implemented from the perspective of Hatch Mott MacDonald (HMM). Launched in 1996 with 35 transit and tunneling staff, HMM has grown to be a multi-disciplinary consulting engineering firm with 2,300 staff in 65 offices across North America. Hatch Mott MacDonald’s parent companies, Mott MacDonald (MM) and Hatch, have a combined staff of 23,000 operating in more than 140 countries.
“A fundamental focus of the business is delivering innovation solutions that are pragmatic and constructible,” said Randy Essex, HMM’s North American Practice Leader. “MM and HMM share tunneling-related innovations so that diverse clients can benefit from a global knowledge base.”
Below, we highlight examples where innovations have been leveraged among a number of recent and ongoing projects.
Toronto-York Spadina Subway Extension/Eglinton-Scarborough Crosstown LRT, Toronto
Following a successful relationship on the Sheppard Subway Project in the 1990s, the Toronto Transit Commission (TTC) engaged HMM in 2008 to assist with the management and design of the Toronto-York Spadina Subway Extension (TYSSE). The $2.63 billion TYSSE consists of 5.4 miles of new rail service, approximately 4.2 miles of which will be housed in twin-bore, soft-ground tunnels. The line also includes six new cut-and-cover stations, associated cross-overs, cross-passages, storage track and yard connection. HMM, in joint venture with Delcan and MMM of Toronto, has provided overall program management for the project, integrating design contracts held by HMM for the twin tunnels, and six contracts for the cut-and-cover stations held by other consultants.
3D CADD Design
TTC challenged HMM with delivering complete tender documents for the twin tunnels within an accelerated 18-month schedule, including site exploration. In order to meet TTC’s tight design schedule, HMM utilized seven packages within the Bentley software suite to design the tunnels, emergency egress buildings, cross passages, and pocket track structures in a fully integrated 3D model. By integrating all structural, mechanical, electrical and alignment elements into a single model, HMM was able to engage multiple design offices in the design effort, and was able to substantially streamline inter-disciplinary coordination and resolution of spatial conflicts. The 3D imaging capability also allowed TTC and affected third parties to visualize what would be constructed and where, strengthening TTC’s public outreach effort.
Following the completion of the Spadina design, HMM submitted work products to Bentley Systems for its 2011 Awards Competition, and was awarded the “2011 Be Inspired Award” for engineering innovation in the Rail and Transit Category.
“Bentley software enabled HMM to meet critical schedule milestones during execution of the tunnel design for the TYSSE project. Multidisciplinary coordination through use of the 3D modeling environment, and graphical representations were key to enhancing communication and geometric understanding amongst team members, our clients, and our stakeholders,” said HMM’s Gary Kramer, Tunnel Design Manager.
HMM is currently engineering the tunneling portion of Metrolinx’ Eglinton-Scarborough Crosstown (ESC) LRT project, which will involve 3.9 miles of twin-bored, soft-ground tunnels, nine cross-passages, an emergency egress building and the headwalls for seven future cut-and-cover stations. HMM has enhanced its 3D modeling approach with utility mapping, which has further streamlined the process of relocating or avoiding utilities and existing structures along the alignment.
Accelerated Start of Construction
Another innovative element that has helped to drive fast-track project delivery on both the TYSSE and ESC projects is the pre-procurement of multiple earth pressure balance tunneling machines (EPBMs) and the precast concrete lining systems. Following from the successful experience with the Shepherd Subway, TTC asked HMM to again assist them with the pre-procurement of four new EPBMs from Caterpillar/Lovat, and with the design and fabrication of a matching precast concrete segmental lining system. The ESC twin tunnels contract, which is out to tender as this article goes to publication, involves an additional two EPBMs and precast segmental linings.
Compensation Grouting Program
One of the TYSSE stations, York University Station, will be located in proximity to the York University campus, which has a student and faculty population of about 40,000. The station is situated in the campus commons, shoe-horned in between two campus structures, the Schulich Building, which is part of the business school, and the York Lanes building, a campus retail mall. Given the inability to move the tunnels out from beneath the Schulich building, and the sensitivity of the structure, HMM developed a compensation grouting program to protect the building during tunnel construction. The use of the method was first introduced in North America on HMM’s St. Clair River Railway Tunnel Crossing in the mid 1990s.
Using three access shafts adjacent to the structure and a fanned array of ported grout injection tubes situated above the twin bore tunnel and below the Schulich building’s foundations, grout will be able to be injected at specific pressures and locations to compensate for any settlement that occurs above the tunnels, thereby mitigating impacts on the structure itself. Utilized in conjunction with a ground and structure instrumentation system, all parties will be able to track building performance as the EPBMs are advanced under the structure.
Victoria Station Upgrade Project, London
Victoria Station is the second busiest station on the London Underground (LU) tube network. There are two inter-connected station areas on different levels, with subterranean platforms serving the District and Circle Line and deeper underground platforms serving the Victoria Line. The existing station was never intended to handle the current service load of 80 million passengers annually, resulting in severe overcrowding at peak periods. With a target to increase the station’s capacity by more than 50 percent, LU selected MM to engineer the massive $1.1 billion Victoria Station Upgrade (VSU) project.
MM was initially commissioned by LU in December 2006 to provide full production design and advisory services. Subsequently, in May 2010, MM’s contract was novated to the selected contractor, Taylor Woodrow and BAM Nuttall JV.
The VSU project includes enlargement of the existing Victoria Line ticket hall, creation of an additional ticket hall and entrance, new pedestrian tunnels to ease passage within the expanded station (constructed with sprayed concrete linings through jet grout stabilized water bearing gravels), improvements associated with passenger evacuation, access for emergency services, and ventilation. Elements include nine new escalators, eight new elevators for step-free access, and modernization of the areas of the station not affected by the new works. An important feature is that this major upgrade must be carried out without impacting ongoing passenger services.
BIM – An Essential Engineering Tool
Given the extreme complexity of the existing works, and the significant associated service- and structure-related risks, building information modeling (BIM) was seen as an absolutely essential tool in carrying out the planning, design and construction phases of the work. “We have pioneered new uses of BIM. For example, to facilitate the tunneling works, we are creating a solid jet grout block by threading columns between existing utilities with incredibly tight tolerances, whilst accurately taking off volumes and quantities. Without BIM this approach to minimizing risk simply wouldn’t be possible,” MM’s design manager Rob Dickson said.
The model was an LU engineering requirement. Secant piles forming the walls of the new north ticket hall are positioned within 10 ft of the culvert carrying the River Tyburn. The passenger tunnel linking the new ticket hall to the Victoria Line ducks under the culvert and scrapes over the southbound Victoria Line platform tunnel with only inches to spare. An escalator squeezes between the twin bores of the north and southbound platform tunnels, with a mere 12 in. clearance.
“BIM is being used to resolve an incredibly complex spatial puzzle so that the new and old come together seamlessly – so everything fits the first time,” Dickson commented. “BIM is being used to check the very fine construction tolerances involved. Another success is that we’ve been able to take LU’s maintenance engineering staff, a key project stakeholder, on a virtual fly-through within the model, thereby addressing their concerns and obtaining their buy-in to the design. ” Prior to HMM’s winning Bentley’s Be Inspired Award in 2011, MM won the same award in 2010 for its BIM successes on the VSU Project.
Structure Instrumentation and Performance
A further challenge for the project is the protection of historic and newly constructed structures and facilities that border Victoria Station, which could be affected by the works. Here, MM has leveraged a ground and structure performance real-time monitoring system that it helped evolve for the Amsterdam North-South Metro Line dating back to 2001. An important component involves the positioning of robotic total stations (remotely controlled electronic distance measuring (EDM) devices) at strategic locations that read prisms installed on selected structures. An automated database management system reads the prisms, downloads the data for review and analysis, and conveys warnings if and when threshold levels of displacement are exceeded. The system provides two important functions on the VSU project: the ability to detect early stages of displacement and allow timely implementation of mitigation measures; and the creation of a baseline of deformation readings that may indicate no movement whatsoever, thereby protecting LU and the contractor against unfounded third-party damage claims.
David Cook, who leads the MM monitoring team, said that “VSU has enabled us to apply our successful monitoring experience working in historic Amsterdam to equally sensitive conditions in central London.”
Crenshaw/LAX Transit Corridor Project, Los Angeles
HMM has been leading a team in the development of preliminary design and design-build procurement documents for the Crenshaw/LAX Transit Corridor Project for the Los Angeles County Metropolitan Transportation Authority (Metro). The project consists of approximately 8.5 miles of new light rail infrastructure including bored tunnel, cut-and-cover tunnel, at-grade and elevated line along with six new stations. The Crenshaw Line will extend from a terminus on Aviation Boulevard near LAX Airport to a new underground station near the Expo Line in downtown LA.
In contrast to the TYSSE project, where a fully integrated BIM model helped deliver 100 percent design and procurement documents, BIM technology was used on the Crenshaw Project to target two key project elements. One was the modeling of the two underground stations, where existing infrastructure and utilities were incorporated into a single model that facilitated space planning and preliminary design of the proposed bored tunnels, station envelope and access shafts.
The second element was the simulation of surface-based construction planned in proximity to LAX. Required to secure LAX official approval for construction, HMM’s BIM modeling helped LAX officials visualize the planned construction work from pilots’ perspectives as they land aircraft at LAX. The simulations were used to establish a construction clearance envelope that avoided runway glide slopes – the imaginary plane that serves as a lower boundary for landing aircraft. Using simulation and visualization techniques, HMM was able to assure LAX officials that Crenshaw construction would not compromise airport safety or operations. Achieving this important approval helped keep the project on schedule.
East Side Access Project, New York
The East Side Access project is a $7.3 billion rail link project that will give commuters on the Long Island Rail Road a “one-seat ride” into Grand Central Terminal, which is located on the east side of Manhattan. The largest single public infrastructure project being carried out in North America, it is incredibly complex. “We’re building a major new transport link in one of the world’s most densely developed cities,” commented Andy Thompson, HMM’s Construction Manager for the project. Since 2000, HMM has been providing program and now construction management services for the New York Metropolitan Transportation Authority. Given the highly variable ground conditions found in Manhattan and Queens, the project has demanded a broad range of underground construction technology – rock TBMs, drill-and-blast excavation, roadheader, NATM and slurry shield tunneling.
A Team Approach to Innovation
The number of innovations achieved on the ESA project could easily fill an article itself. The following is just one, but it underscores how teamwork underground can benefit everyone. One of the project’s requirements is for twin bores coming from Queens to feed eight platforms housed within two new station caverns located below the operating terminal. This geometric transition mandated the need for six bifurcation or “wye caverns” underground. Using drill-and-blast methods in conjunction with roadheaders, the first wye cavern took six months to complete. During the planning for this initial effort, one of HMM’s resident engineers, Ed Kennedy, recalled a technique used previously on the Chicago TARP project. Several crew members from that project working with ESA Contractor Dragados/Judlau JV, talked up the concept, and it was eventually trialed. The concept consists of the following steps:
Step 1: Advance the TBM along an initial bored length
Step 2: Back the TBM up to a location short of the planned wye
Step 3: Backfill a 200 ft length of the bore with lean-mix concrete
Step 4: Advance the TBM into the lean concrete and slowly turn the TBM onto the new alignment
Step 5: Remove the residual concrete from the initial bore
Step 6: Trim the concrete gore point with a roadheader to form a 3-ft wide pillar
This innovative technique was utilized successfully on the five remaining wye excavations. With each subsequent attempt, the Contractor’s crews were more efficient in their execution. The modified approach for the five remaining wyes saved a total of 130,000 cubic yards of rock excavation and 20 months’ schedule. Because all muck from Manhattan had to be conveyed back through the Manhattan tunnels, under the East River, and out through the mining shaft in Queens, reduced excavation volume translated into a significant savings in muck removal disposal cost as well. In addition to facilitating the five wye transitions, the concrete backfill method was also used to help shorten the overall lengths of the two GCT caverns. “It took teamwork with the contractor to help make this work,” Thompson and Kennedy agreed. “We’re gratified that this idea was taken on board to the success of the project.”
Euclid Creek Tunnel, Cleveland
The Euclid Creek Tunnel (ECT) Project is the latest element of the Northeast Ohio Regional Sewer District’s (NEORSD) $3 billion effort to dramatically reduce combined sewer overflows (CSOs) in its service area. The first deep storage tunnel to address the northeastern part of Cleveland, the 3.4-mile long, 24-ft diameter tunnel, shafts and appurtenant facilities will be used to collect, store and convey CSOs to the NEORSD’s Easterly Wastewater Treatment Plant for treatment.
The subsurface conditions along the tunnel alignment will consist of thinly bedded shales and interbedded siltstone of the Chagrin shale formation. Past rock tunneling in the Cleveland area has utilized two-pass lining systems consisting of combinations of rock reinforcement and steel rib and lagging, in conjunction with a cast-in-place lining. However, a number of these projects have had to deal with the occurrence of gas, localized tunnel instability due to rock wedges and blocks, and time-related rock deformations associated with slaking, overstress or both. Because relatively high horizontal in-situ stresses are expected to exceed the rock mass’ compressive strength, spalling behavior is anticipated during tunnel excavation. Recently, the Niagara Power Tunnel endured delays and cost over-runs because the design-build team’s two-pass construction method was not able to cope with overstressed ground. To avoid similar risks on the ECT, as well as address potential gas infiltration concerns, HMM designed the ECT Project with a one-pass, bolted and gasketed lining system.
Tailskin Grout System
HMM’s project risk register identified two lining-related risks: the potential ovaling of the large-diameter ring due to inadequate annulus grouting; and the need to consolidation grout broken rock above the crown caused by spalling. HMM specified a tailshield grouting system that will utilize a fast-set, two-component grout to immediately grout the annulus and support the segment rings as mining advances. As this application involves an open face, rock TBM, the quick set time of the grout is also needed to mitigate grout travel forward of the shield toward the TBM cutterhead. Contact grouting through segments will be performed to fill any gaps or voids behind the tunnel lining. (Insert Figure 13, ECT TBM Shield)
The fast-set, two-component tailskin grouting approach has been or will be utilized on seven other HMM tunnel projects including the TYSSE, ESC and Southeast Collector projects in Toronto, the ESA tunnels in Queens, the New York Harbor Siphon Project, the Port Mann Water Main in Vancouver, and the Alaskan Way Viaduct Replacement Tunnel in Seattle. The Euclid Creek Tunnel project provides the added twist in that it will be mined with a non-pressurized TBM. Mike Vitale, HMM Project Director and Deputy Tunnels Practice Manager based in Cleveland, said: “Everyone involved understands the importance of getting the grouting right at the outset; the specs include a fairly extensive drilling and proofing program in the first 100 rings so that we get the coverage needed. McNally/Kiewit, the contractor, is also involved on our TYSSE and Port Mann projects – so lessons learned will be shared among three projects, not just one.”
The following HMM staff contributed to this article: Randy Essex, Gary Kramer, Rob Dickson, David Cook, Ed Kennedy, Andy Thompson and Mike Vitale. Additional illustrations are available online at www.tunnelingonline.com.