Tunneling trends

November 2013 » Exclusive
Technologies, designs, materials, and evolving demographics and infrastructure needs point to an increase in U.S. tunnel projects.
Bob Drake
A worker clears the way for TBM breakout at the North Shore Connector LRT project in Pittsburgh.
Photo: Paul Roy, AECOM

Within the last decade, civil engineers have helped expand the boundaries of tunnel design and construction globally and – significantly – in the United States. Current and recently completed transportation and water tunnels across the country are setting records and refining technologies and designs that could spark a new era in tunneling. In this CE News exclusive, five tunneling experts offer their observations on progress during the last 10 years and the promise for the sector during the next decade.

AECOM
Paul A. Roy, P.E., senior vice president

How has tunneling worldwide and in the United States changed or progressed during the last 10 years – both from an engineering/technology/construction perspective and from infrastructure owners' perspective (i.e., market opportunity and acceptance)?

Tunneling continues to evolve based on new technology. Tunnel Boring Machines (TBMs) have continued to progress in speed, adaptability, and safety to unique difficult ground conditions. Large-bore TBMs are beginning to show up in the United States that 10 years ago would only have been seen abroad. The largest soft-ground TBM in the world is working in Seattle. At approximately 57 feet in diameter, the expected success of this TBM will promote the use of larger TBMs in the United States. Although the large-bore TBM in Seattle is for construction of a highway tunnel, the application and success will promote large-bore tunnels for transit systems, which are typically smaller, twin-bored tunnels and cut-and-cover stations. This larger size TBM will enable not only the running transit, but also the station, which will result in minimal surface disturbance and third-party impacts. TBM technology and grouting technology have also developed to reduce potential settlements to the range clients are expecting – "net zero" settlements.

Monitoring of TBM drives with the use of real-time GPS systems has continued to expand, allowing TBM driving bulls-eye to decrease and the ability to keep TBM drives on target. The skilled labor pool in TBM operation has also improved, allowing TBMs to drive over 400 feet per day in good ground.

The increased evaluation of risk analysis has been a focus of the owners' perspective. They are assessing the "what if" scenarios in more detail, particularly third-party impacts, involvement, and solutions.

What are your expectations for the tunneling market in the United States during the next 10 years and why? What do you expect to be the predominate applications (i.e., road, rail, transit, water, etc.), if any?

As free surface land becomes more inaccessible and expensive, we would expect tunneling for road, rail, and transit to increase over the next 10 years in the United States. Several transit systems in the United States have not constructed critical connections to allow the system to operate at full efficiency. The connections are usually located in dense urban settings where tunneling may be the only acceptable solution.

The tunneling market will also see an increase in tunnel inspection, evaluation, and implementation of state of good repair. The Federal Highway Administration has issued a supplemental Notice of Proposed Rulemaking on tunnel inspections to incorporate into the requirements of MAP-21, the surface transportation law. Some of the changes will require a professional engineer with at least 10 years of experience for program manager, add a national certification requirement and training courses for all team leaders and inspectors, and set timetables for inspections.

Predominate tunneling to occur appears to be in the area of water-related tunnels. Many of the court-decreed extensions to the Clean Water Act of 1972 have already led to an expansion in water tunneling proposals and construction.

What factors and/or technologies have had the greatest impact on tunnel design and construction during the last 10 years?

Major impacts to tunnel design over the past 10 years include design methodology of tunnel liners and waterproofing systems. In the case of precast segmental concrete reinforced liners, the use of special dowelling systems and waterproofing systems have added to efficient design and safer erection methods. The use of fiber-reinforced liners has also increased over the past 10 years, more so in the world marketplace than the United States. The configuration of waterproofing and gas proofing extruded gaskets has provided benefits in repairing any lining leaks post construction.

A major impact to tunnel construction has been the change to many more public-private partnerships (P3s) and design-build procurement of tunnel projects. And this appears to be on the increase in future years.

Paul A. Roy, P.E., senior vice president with AECOM and director of Americas Tunneling Practice, has extensive experience in structural and geotechnical engineering and project management for tunnels and underground facilities.


Arup
Jon Hurt, P.E., CEng MICE, principal

How has tunneling worldwide and in the United States changed or progressed during the last 10 years – both from an engineering/technology/construction perspective and from infrastructure owners' perspective (i.e., market opportunity and acceptance)?

Ten years ago, the United States was noticeably behind the rest of the world in adopting Earth Pressure Balance Machines (EPBMs) and Slurry TBMs and the use of precast concrete segmental linings. When I started on the design of Second Avenue subway in 2002, there were extensive discussions about whether segments were suitable for a permanent lining. Now we are seeing projects in the United States that are leading the world – including the Lake Mead Intake No.3 (an Arup project) with the TBM operating under the highest external pressure ever, and the [Alaskan Way Viaduct Replacement] State Route (SR) 99 roadway project with the largest tunnel diameter.

Globally we have seen increasing mechanization in tunneling in bored tunnels, drill-and-blast, and soft ground sequential excavations. TBM diameters have increased and improvements in soil conditioning have allowed the use of EPBMs in a wider range of ground conditions. There also has been a significant shift from traditional design-bid-build – first to design-build and then on to P3 projects. The overall global market has consolidated and globalized both in terms of the companies involved and in terms of work methods and practices.

What are your expectations for the tunneling market in the United States during the next 10 years and why? What do you expect to be the predominate applications (i.e., road, rail, transit, water, etc.), if any?

The next decade is likely to see steady growth in the number, scale, and difficulty of tunnel projects. The growth of cities and mega-regions, together with the need to replace aging infrastructure, will continue to drive the need for new tunnels. Planning for high-speed rail and mass transit systems has grown in the last five years, providing the promise of more tunnel projects in the transport area. Water supply tunnels will be needed to respond to changing rainfall patterns, particularly in the Southwest. While some combined sewer overflow (CSO) projects may avoid the need for tunnels with a shift to green infrastructure solutions, the limitations in scale and ongoing maintenance costs of these alternatives will mean conveyance and storage tunnels are an inevitable part of the solution to avoiding overflows in many cases.

Lake Mead Intake No.3 – Start Tunnel.
Photo: Arup

In terms of procurement, I would expect to see greater use of private finance and P3 style contracts in the United States, following the global trend. The use of alliancing contracts, intended to encourage collaboration rather than confrontation between owners and contractors, is on the rise in other regions of the world, and it will be interesting to see if they become common in the United States.

What factors and/or technologies have had the greatest impact on tunnel design and construction during the last 10 years?

Without a doubt, with continued improvements in TBM technology, and in particular the ability to have multi-mode machines, now there is no ground we cannot tackle provided we have the right TBM. Along with this we have seen improvements in casting yard equipment and curing for the precast segments, and improvements in gaskets, fittings, and inserts, as well as in the TBM erector equipment and guidance systems. The trend to steel fiber reinforcement has made a step-change to the durability of precast lining segments. And while we still need compressed air for TBM interventions, the change to oxygen mask breathing has meant the previous health risks have been largely overcome. Compensation grouting, combined with the pressure TBM improvements, has resulted in huge reductions in ultimate ground losses and building settlements for soft ground tunneling in the last 10 years.

There have also been some new technologies introduced that have great potential but have not yet been widely adopted, at least in the United States. Four that I particularly like are:

  • electronic detonators for blasting, allowing larger round lengths while significantly reducing vibration, overbreak, and damage to the rock fabric;
  • shaft sinking machines that mechanize and speed up construction;
  • automated robotic segment erectors for installation of segmental linings; and
  • real-time profile control for excavators and shotcrete application.

Jon Hurt, PE, CEng MICE, principal with Arup has a wide range of experience in the management, design, and construction of major tunneling projects. Also leader of Arup's Tunnel Practice, Hurt is responsible for managing resources, training, and knowledge sharing within the firm's tunneling community


HNTB Corporation
Sanja Zlatanic, P.E., chief tunneling engineer

How has tunneling worldwide and in the United States changed or progressed during the last 10 years – both from an engineering/technology/construction perspective and from infrastructure owners' perspective (i.e., market opportunity and acceptance)?

Underground construction has boomed in the last 10 years worldwide. This trend is due to several factors such as the growth of population of cities, demand for sustainable solutions, and the call for environmentally friendly solutions, coupled with advancement of technologies.

The number and size of megacities throughout the world and the associated needs for additional infrastructures has been increasing significantly with the reverse migration toward cities. According to the United Nations, by 2015 over 60 megacities – each with population of over 10 million people – will exist worldwide. It is also expected that by 2030, 60 percent of the world's population will be living in cities. This trend demands sustainable, efficient, economical, and environmentally friendly infrastructure to reduce environmental impacts, enhance visual impact, and minimize surface disturbance.

To meet these needs, the United States and the world in general is more frequently choosing to place transportation infrastructure, utilities, water and wastewater, storm protection, power, and other systems deep underground. Recent advancements in tunneling technologies and equipment have also made underground construction solutions more desired. TBMs have been advanced in size, sophistication, and capabilities resulting in their abilities to excavate larger, faster, and safer tunnels. The Alaskan Way Tunnel, designed by HNTB, features a 57-foot, 4-inch TBM, the largest in the world, and it is being excavated under a highly dense urban environment with limited soil cover and passing within feet under the existing SR 99 viaduct.

What are your expectations for the tunneling market in the United States during the next 10 years and why? What do you expect to be the predominate applications (i.e., road, rail, transit, water, etc.), if any?

The tunneling market will continue to grow. The American Society of Civil Engineers estimated that within the next five years over $1 trillion needs to be invested in infrastructure. I believe that over $100 billion will be in tunnels and underground construction projects. Based on the trend we see in growth of megacities, we expect transit and water/wastewater will be the dominant market sectors for tunnel projects. In addition, high-speed rail will require significant investments in tunnels and underground structures. For example, transit expansion programs in Los Angeles, New York, Baltimore, and Seattle will result in significant underground and tunneling projects. In addition, California's High Speed Rail Program and Amtrak's Gateway and Northeast Corridor Improvement Program will require expenditures of tens of billions of dollars each. Water conveyance programs in New York and the Bay Delta Program in California are monumental, multibillion-dollar programs. In addition, many older cities are implementing and will continue to implement CSO programs.

In order to meet the needs in financially strapped cities with limited federal funding available, we see a movement toward privatization using the P3 delivery method. For example, the Second Midtown Tunnel in Norfolk, Va., and the Port of Miami Tunnel are being delivered as P3. Also, Baltimore Purple Line will be delivered by P3, availability payment approach; similarly SR-710 and Sepulveda Pass programs in Los Angeles will most likely be delivered using P3 procurement strategy with appropriate tolling.

The 2013 opening of the Tom Lantos Tunnels at Devil's Slide in San Mateo County, Calif., marks a new era for the California Department of Transportation. For the first time in nearly 50 years, tunnels again are a realistic option for increasing mobility and safety in the state. This was the first tunnel in California to use the New Austrian Tunneling Method.
Photo: Copyright Jeffrey G. Katz, courtesy of HNTB Corporation

Another trend we expect to see more in the next 10 years in tunnel construction is design-build delivery approach. In this approach, owners are benefiting from accelerated schedule; innovative alternative designs; contractors' input to meet construction means and methods; advancement of the procurement of long lead items; and a simplified accountability, responsibilities, and risk sharing.

What factors and/or technologies have had the greatest impact on tunnel design and construction during the last 10 years?

Advancement in the automation of tunnel construction and innovations in tunneling equipment and technologies for all type of tunnels have resulted in the ability to build tunnels faster, cheaper, and safer. Tunnel construction is a cyclic and linear operation. The ability to overlap activities and to provide repetitive actions improves production rate and cost. For example, recent advancement in TBM design such as higher thrust and torque capabilities, precise control of face pressure, ability to change cutters under atmospheric pressure, remote sensing, laser guidance, etc. resulted in the ability to construct larger tunnels in more challenging circumstances. Similarly, advancements in the observational methods and technologies expanded the use of the New Austrian Tunneling Method (NATM) in the United States. Recently, HNTB and Caltrans opened the Devil's Slide Tunnel in California, which was constructed by the NATM method. This project had hugely challenging technical and environmental constraints, which were successfully managed, but also helped advance the NATM technology in the United States.

Sanja Zlatanic, P.E., chief tunneling engineer for HNTB Corporation, has 25 years of experience with tunnels and complex underground structures. She has been in a leadership role for many large transportation projects in the United States and internationally. Since joining HNTB, Zlatanic has been leading independent design verification of the Istanbul Strait Road Crossing Tunnel project in Turkey and participating in the expert review panel overseeing design of the SR 99 Alaskan Way Viaduct and Seawall Replacement project in Seattle.


MWH Global
Greg Raines, P.E., M.Eng., tunneling practice leader

What are your expectations for the tunneling market in the United States during the next 10 years and why? What do you expect to be the predominate applications (i.e., road, rail, transit, water, etc.), if any?

We see the underground market for wet infrastructure being driven by several factors including environmental mitigation, aging infrastructure, scarcity of resources, demographic changes, and sustainability. These factors influence water supply, conveyance, rehabilitation, storage, and hydropower. For example, in the United States, agencies such as the Environmental Protection Agency have regulatory mandates which require cities to reduce sewage pollution into rivers, lakes, and oceans where storage and conveyance tunnels have proven to be effective. We see future growth in tunnel works due to aging infrastructure particularly for cities and communities where water is being conveyed long distances between locations where water is abundant to those where it is scarce. We are also seeing development of intake and outfall tunnels for water supply related to desalination.

In addition, the significance of renewable energy as a part of the world energy portfolio has huge potential for the hydropower industry and, as a direct result, tunneling. Emerging countries with rainfall and relief have been investing in hydropower as part of their overall development. In the United States, where only limited new hydropower facilities are being developed, we are seeing an increased role for pumped storage, which has a huge potential when paired with other forms of renewable energy such as solar and wind.

What factors and/or technologies have had the greatest impact on tunnel design and construction during the last 10 years?

Advances in TBM technology have altered the industry in significant ways and produced results never before imagined. MWH has been serving as the owner's engineer in joint venture with CH2M HILL on the Lake Mead Intake No. 3, an important tunneling and water intake project that benefited directly from industry advances. The work being completed under Lake Mead resulted in a TBM operating under the highest external pressure ever successfully attempted to date. This project would never have been possible if theses advancements weren't being developed concurrent with the preliminary design. In Pakistan, our team is working on a hydropower project in which we were able to convert a drill and blast project into a TBM project which is under high cover in squeezing ground. This is a result of the advances that TBM designers are bringing to the process that we as civil engineers are able to take advantage of when developing tunneling concepts.

Additives have also benefited tunneling greatly. Whether they are used in conjunction with pressurized face TBMs where foams, bentonites, polymers, surfactants, and other additives are used with TBMs to allow them to operate in a greater range of conditions or with concrete and grout additives, where rheology of the materials can be modified to facilitate construction, while at the same time giving us higher quality concretes and grout. The use of these specialized additives has really improved over the years, or at least our understanding of how to use them. This has given us many more application options, while still working with the same basic materials we are used to.

On the engineering front, significant advances have occurred in the last decade. Modeling and engineering analysis capabilities have increased greatly resulting in our ability to model more complex ground/lining interaction, including 3D. As a result, we are able to complete our projects faster and at a lower cost, despite working in ever more difficult ground. In addition, the amount of information available to our teams, a result of information technology advancements, has resulted in real-time monitoring capabilities. We can now be linked to remote locations throughout the entire construction process. This is proving increasingly valuable, allowing for more informed decisions out in the field. The industry has been drastically altered by these advancements and we are achieving results that 10 years ago I would have never imagined possible.

Greg Raines, P.E., M.Eng., tunneling practice leader, MWH Global, has more than 30 years of experience in tunnel engineering which includes planning, design, and construction management. He lectures annually at the Colorado School of Mines tunneling short courses. At MWH, Raines is responsible for project development, technical direction, and risk management for tunnels, and underground structures constructed throughout the world.


Parsons Brinckerhoff
Joe O'Carroll, P.E., vice president

How has tunneling worldwide and in the United States changed or progressed during the last 10 years – both from an engineering/technology/construction perspective and from infrastructure owners' perspective (i.e., market opportunity and acceptance)?

In the last decade, increasingly more powerful TBMs, combined with high-strength cutters and earth pressure balance (EPB) and slurry face capabilities, have continued to improve all aspects of soft ground tunnel excavation. Production rates continue to climb as technology improves and larger, more powerful machines are manufactured. This is despite the fact that tunnels are becoming larger and more complex, the ground conditions in which they are excavated more difficult, and the access and working requirements more restrictive. Projects such as the Alaskan Way Viaduct Replacement Program SR 99 tunnel in Seattle, the Port of Miami Tunnel in Florida, and the Eurasia Tunnel in Istanbul might not have been contemplated 10 years ago.

In particular, innovations in EPB TBMs with enormous power and torque capabilities, combined with advances in soil conditioning technology, the ability to service the TBM cutterhead in free air, and advancements in precast segment lining designs have transformed the way engineers now approach the design of highway, rail, and water conveyance tunnels in dense urban areas. Single-bore tunnels in the range of 45 feet to 57 feet in diameter are replacing conventional twin-bore highway and transit tunnels. This offers owners the opportunity for cost-effective solutions with less disruption to their cities and business centers and fewer impacts to adjacent properties and infrastructure.

What are your expectations for the tunneling market in the United States during the next 10 years and why? What do you expect to be the predominate applications (i.e., road, rail, transit, water, etc.), if any?

Tunnel construction in the United States has been buoyant over the past decade. The prospects for the next decade appear a bit more challenging as the federal government and states continue to face increased revenue generation and funding challenges. States will have to use more and more existing funding to maintain existing infrastructure, and make more use of alternative financing schemes such as P3s to finance new construction.

During the next few years we will see the completion of projects such as the Port of Miami Tunnel, New York's East Side Access and Second Avenue Subway, and the record-breaking 57.5-foot excavated diameter SR 99 tunnel in Seattle. The industry will then be looking to California to maintain the momentum in the tunneling business. Los Angeles's West Side Extension, Regional Connector, and Crenshaw Subway projects, combined with the California High-Speed Rail, Bay Delta Water Conveyance Tunnels, and I-710 Highway, offer the opportunity for over 150 miles of new tunnel construction.

In addition to the District of Columbia's 10-year Clean Rivers program and Maryland Transit Authority's Red Line project, the East Coast will be looking to Amtrak's North East Corridor Capital Improvement Program to generate significant investment in new tunnel infrastructure. Water conveyance and wastewater management tunnel projects will continue to dominate the tunnel market in the Midwest and Central regions of the United States over the next decade.

What factors and/or technologies have had the greatest impact on tunnel design and construction during the last 10 years?

With the help of modern equipment for rapid excavation, high-quality construction materials, and improved ground support installation, complex and challenging underground structures such as Chinatown Station in San Francisco, Beacon Hill Station in Seattle, and Tysons Corner in Washington, D.C., have been designed – in the case of Beacon Hill and Tysons Corner, safely constructed using sequentially excavated mining methods in practically all types of soft ground at great depth and with shallow cover and high groundwater. Over the past 10 years, however, not one single factor or technology could be said to have had the greatest impact on tunnel design. Collectively, advancements and innovations in tunnel ventilation and fire life safety design, geotechnical and seismic engineering, tunnel lining design, security and blast design, modern instrumentation and monitoring equipment, the use of virtual design and construction (3D/4D modeling), and a greater appreciation for risk management have all contributed toward larger, longer, safer, and more user-friendly tunnels and underground spaces that continue to present cost-effective solutions to building much-needed infrastructure in cities where aboveground space is a rapidly decreasing commodity.

Joe O'Carroll, P.E., is a vice president in Parsons Brinckerhoff's Geotechnical and Tunneling Technical Excellence Center and currently serves as the tunnel practice leader in California. He has more than 30 years of experience in design, construction, project management, and risk management on major tunneling projects in Europe, Asia, and the United States.


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