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By Lei Fu

In the wake of the collapse of the ceiling panels in the I-90 section of the Central Artery/Tunnel (CA/T) Project in 2006, the long term performance of tunnels became the focus of the tunneling industry. At the time of the accident, the tunnel had been open to traffic for about 10 years. This paper will discuss design methods and considerations to improve the long term performance and durability of a tunnel. The major problems found during the inspection of several tunnels will also be presented and the causes for these problems will be discussed.

Jan 1, 2008

By Paul A. Roy

The North Shore Connector Project for the Port Authority of Allegheny County constructs twin Tunnel Boring Machine (TBM) tunnels through cohesive soils and rock beneath the Allegheny River and a narrow city street in Pittsburgh, PA. The tunnel alignment includes an historic building on shallow foundations, modern buildings on deep foundations, and an office building constructed directly over the alignment during the design of the tunnel sections. This paper provides an overview and update of the general site conditions, TBM tunnel design, and support of excavation for the TBM launching pit. Deformation limits, ground improvement, monitoring and mitigation plans are also discussed.

Jan 1, 2008

By John Reilly

The author?s paper at RETC 2007, ?Alternative Contracting Methods? addressed strengths and weaknesses of DBB+DB and introduced Construction Manager/General Contractor (Portland model) and Alliancing (Australian model). Considerable interest in these was expressed by several public agencies at that Conference and at the presentation. The author is assisting the Washington State Department of Transportation (WSDOT) and the Toronto Waterfront Revitalization Corporation (TWRC) with possible implementation of Alliancing. WSDOT is evaluating ways to do this and is considering a delivery methodology, under existing Legislation, based on the CMGC Portland model with incentives and disincentives, moving towards Alliancing. This paper will build on the 2007 paper and update implementation considerations.

Jan 1, 2008

By John Rudolf

Metropolitan Washington Airport Authority is currently undertaking the first Phase of Metro?s Extension to Northern Virginia. A wide range of tunnel options was considered for the Tysons Corner segment that involves about 20,000 feet of track and four stations. After consideration of many options that involved EPBM single track tunnels, NATM tunnels and large bore tunnel concepts for the entire Tysons alignment, the design now being progressed into construction involves two 520 meter (1,700 feet) long soft ground NATM tunnels with several hundred feet of cut-and-cover construction. The paper discusses the process that led to selection of the short NATM tunnels as the most feasible of the options considered for Tysons.

Jan 1, 2008

By Joe Roby

Rolling disc cutters are the business end of hard rock and mixed face tunnel boring machines (TBMs). Since their first successful employment on a TBM over fifty years ago, disc cutter technology has constantly evolved, allowing modern TBMs to excavate very hard and abrasive rock efficiently. Disc cutters have also been employed successfully on earth pressure balance (EPB) and slurry machines, cutting rock under water and ground pressure. The range of materials excavated by machines today is broader, excavation rates higher and cutter costs lower than ever before, proving the value of investment in cutter development. This paper describes recent improvements in disc cutter components including cutter ring materials and processing, as well as improvements in lubricants, bearings, seals and cutter condition monitoring. These developments have resulted in more reliable cutters capable of operating in a wide range of geological conditions. Ultimately these improvements result in a better value for both contractors and project owners.

Jan 1, 2008

By Y. Nien Wang

The Devil?s Slide portion of Highway 1 between Pacifica and Montara is often closed due to the instability of the adjacent slopes. Following many years of public input and careful evaluation of alternatives, Devil?s Slide will be by-passed via two inland tunnels, providing a safe, dependable highway between Pacifica and Montara. For the twin tunnels, each 9m diameter tube will accommodate only one traffic lane. Each tunnel tube will accommodate a 3.6 meter roadway, 0.6 meter and 2.4 meter inside and outside shoulders respectively, and 1.2 meter walkways on each side. Cross passages will connect the bores at about 120 meter intervals and jet fans will provide tunnel ventilation. The twin tunnels are approximately 1,250 meter long and 9 meter wide. Excavation will progress from south to north using tunneling techniques that rely on inherent rock strength for support known as the New Austrian Tunneling Method (NATM). Both tunnels will be excavated at the same time, one tunnel face approximately 40 meters ahead of the other. Staggering the tunnels reduces the likelihood of damage from blasting in alternate tunnels. The work schedule is 24 hours a day, 7 days a week resulting in a 24-month timetable to break through to the north portal.

Jan 1, 2008

By Wern-ping (Nick) Chen

In concrete lined tunnels, formwork removal timing may be controversial. Contractors seek to strip the form as soon as possible, and designers seek to keep the formwork in place as long as practical to protect the fresh concrete. Formwork removal timing is normally specified as a function to its insitu concrete strength. This approach may work for smaller diameter tunnels, but fallacy occurs when applying this approach to larger diameter tunnels, since a larger diameter would experience more displacement than a smaller diameter tunnel from its own weight. Excessive deformation may fail a tunnel to meet its roundness criterion and overstress the lining causing cracking or falling from the crown. This paper presents a contractual mechanism to mitigate this issue.

Jan 1, 2008

By L. Alan Weakly

Global warming is a political reality in the United States today. The actual impact of the continued utilization of fossil fuels is not known and is open to debate. However, the growing concern about the continued use of these fuels is problematic. There are technologies available to us today that would permit America to meet its future energy demand and not contribute to global warming. The inconvenient reality is that fossil fuels cannot completely be replaced with energy conservation and the use of wind, solar, hydroelectric, geothermal and nuclear energy. The connection between the greenhouse effect and global climate change was first identified by physicist John Tyndall in the 1860s. To prove the greenhouse hypothesis, Roger Revelle and his research team started measuring carbon dioxide concentrations in the earth?s atmosphere in the early 1960s (Becker, 2007). With the rising concern about global warming, scientists throughout the world have been obtaining surface and air temperature data. Scientists have also been comparing CO2 concentrations found in glaciers throughout the world with theorized annual temperatures. Data for both dates back 1,000 years. Armed with this data, many nations of the world and the United Nations Intergovernmental Panel on Climate Change (IPCC) have concluded that climate change is a reality. The IPCC also concluded that this climate change is the result of mankind?s consumption of fossil fuels and that catastrophic consequences will occur on a

Jan 1, 2008

By Seal. Thom

Large heap leach operations around the world contain significant under-leached metal values that present recovery challenges to operators. The first challenge is to find the location of the highest inventory. High resolution resistivity ? has proven sensitive enough to detect such zones in the interior of heap leach pads to target treatment or re-leaching. Newmont Mining Corp. has adapted the high pressure fracturing technology, used in oil wells to stimulate select zones in heap leach pads to add reagents in 3-D for re-leaching, changing zonal chemistry for improved recovery and heap closure. High Resolution Resistivity ? is able to subsequently monitor injected solution flow and determine directional permeability during Hydro-Jex stimulation. The combination of these technologies has shown strong economic success, for selecting targets in the heaps and monitoring solution application. These technologies are now available to the mining industry for adoption.

Jan 1, 2008

By Samuel J. Gambino

Preliminary recommendations for the Upper Northwest Interceptor 1&2 specified installation of reinforced concrete pipe using pipe-jacking methods. However, a larger one-pass tunnel constructed using precast segmental lining would provide additional storage volume. The risk of encountering unexpected conditions or events and the resulting cost impacts could differ significantly for these two options. A probabilistic life-cycle cost analysis of these alternatives was performed. This paper discusses the construction alternatives considered, the risk assessment methodology used to evaluate these alternatives, the input parameters and risk factors used in this analysis, and the recommended project which is currently being constructed.

Jan 1, 2008

By William Connell

NFPA 502, Standard for Road Tunnels, Bridges and Other Limited Access Highways establishes minimum fire protection and fire life safety requirements for road tunnels, bridges and other roadways where access by emergency responders is physically limited. The 2008 edition of NFPA 502 represents the Technical Committee?s consensus of current best practice for fire protection and life safety requirements for road tunnels, bridges and similarly limited access highways. Research of national and international test programs, design guidelines and regulating standards was per-formed and considered in an effort to establish a singular, comprehensive document representing a recognized base threshold of fire safety in these type facilities. This paper provides an overview of the more significant revisions including the application of fixed fire suppression systems, guidance on tenable environment, protection of structure and dangerous goods transport.

Jan 1, 2008

By Mike Tracy

This section of the Handbook deals with general principles to be evaluated in the development of a mining operation. It addresses the major issues that must be examined to fully evaluate a mining venture. Of course, one of the main topics to be evaluated is mine planning, which is covered in more detail in other sections (13, 17) of the Handbook and should be referenced in mine development projects. The topics to be discussed in this introduction include equipment and supplies, infrastructure, utilities, and project management. In any of the aspects mentioned, the current existing conditions at or near the mine site must be evaluated. This will include assessment of current use of utilities, infrastructure, housing, equipment suppliers, etc., as well as anticipated growth, both in the supply aspect of these systems as well as projected usage on these systems. After full assessment of both these aspects, an evaluation must be made as to the requirements the project will place on these items. Assessment must be made as to any up-grades required to bring the project on line, what impact the project will have on existing or expanded systems, and anticipated future growth impacts on support systems not only of the project but of other surrounding industry and urban devel-opment

Jan 1, 2008

By Richard Hanke

Tunnel construction on the Brightwater Conveyance System?s East and Central contracts required ground modifications of the existing site soils, comprised of sandy alluvium to very dense glacial till, to assist with both hand-mined and TBM tunneling operations at vertical access shafts. The ground modification program was completed with a modified double fluid jet grouting system to construct continuous overlapping soilcrete columns to depths up to 94-ft below existing grade. This paper presents the sequence and methodology for the ground modification work and capabilities of jet grouting for structural support and groundwater control in the challenging soil profile present at the Brightwater Conveyance System Project.

Jan 1, 2008

By Luke Erickson

San Francisco Public Utilities Commission is planning to replace 5 miles of pipeline under San Francisco Bay. The tunnel will be constructed using an Earth Pressure Balance (EPB) TBM and will be the first TBM-driven tunnel under the Bay. The alignment passes under environmentally sensitive habitats, through interbedded layers of sands and clays, and through a buried bedrock ridge. This paper discusses the geotechnical characterization and anticipated tunneling conditions and presents the analysis of various construction methods that resulted in the selection of an EPB TBM. Considerations related to tunneling with an EPB TBM are described in detail, including ground conditioners, TBM cutterhead wear, muck control, and squeezing ground.

Jan 1, 2008

By Paul Headland

The Washington Suburban Sanitary Commission (WSSC) has recently completed design for the Bi-County Water Tunnel Project. The project will include a 10-foot diameter, 5.3-mile long hard rock tunnel located within the Piedmont Physiographic Province in Montgomery County, Maryland. The rock formations present along the alignment are comprised of igneous and metamorphic lithologies. This paper presents the steps taken to characterize the complex geology along the tunnel alignment into a single ?Engineering Unit? based upon the intact rock and rock mass properties. The Rock Mass Rating (RMR) system is planned to be used as the basis for dividing the ground into three ?Excavation and Support? classes. This RMR approach was selected to establish contractual baselines as presented in the Geotechnical Baseline Report (GBR) and is intended to facilitate management of the ground support characterization during construction.

Jan 1, 2008

By C. T. Agouridis

Head-of-hollow fills or valley fills have gained national attention due to increasing environmental concerns, particularly with regards to headwater stream loss. Researchers at the University of Kentucky in conjunction with outside scientists and consultants in the fields of stream restoration, wetland restoration, and mined land reclamation have developed new design methodologies for creating a headwater stream system for a head-of-hollow fill in eastern Kentucky. The design was largely built on the Forestry Reclamation Approach (FRA), which encourages a non-compacted spoil medium to promote tree growth, in an effort to address concerns related to water quantity and quality as well as habitat development. The major components of the design included 1) modifications to the crown geometry, 2) compaction of the crown to control infiltration, 3) utilization of natural channel design techniques, 4) use of the FRA to promote tree growth, 5) creation of ephemeral channels and vernal ponds, and 6) implementation of a novel bioreactor-wetland treatment system to improve water quality.

Jan 1, 2008

By Jimmy Thompson

The Santa Clara Valley Transportation Authority is designing the Silicon Valley Rapid Transit Project in San Jose, California. The project includes 6.9 km (4.3 miles) of twin-bored tunnels to be constructed through downtown San Jose using two earth pressure balance machines (EPBMs). This paper begins with a project description and update of the project status followed by a description of the relationship between anticipated ground conditions and EPBM requirements. Topics addressed include soil conditioning, abrasion resistance, annulus grouting, face pressure estimation, additional pressure control devices and control measures to limit over-excavation and settlement.

Jan 1, 2008

By H. Maleki

Interwest Mining Company has been collecting geologic data within the last decade in preparation for underground mining of extensive coal reserves in its Bridger Coal property in southwestern Wyoming. During a preliminary data collection program in 2000, Interwest Mining completed geologic investigations, including surface mapping, drilling, aerial photography, rock testing, and limited groundwater investigations. Core from 12 exploration boreholes in the area of interest was tested to determine the mechanical properties of the coal seam and the immediate roof and floor for evaluation of the feasibility of underground mining. Geologic investigations identified the presence of one 7-to-17-ft-thick coal seam throughout the reserve under 1400 ft of cover. During a geotechnical feasibility study in 2002, the authors reviewed available data while completing comparative analyses identifying critical deficiencies in these data. The study projected moderate-to-difficult mining conditions, considering the weak nature of near-seam strata and depth of cover, and thus recommended limiting the longwall reserves to an overburden depth of less than 900 ft. These shallow remaining reserves were located at depths within regional mining experience to justify longwall mining methods. Based on a critical examination of available data, Bridger proceeded with more detailed data collection to improve understanding of the depositional and structural setting of the reserve, hydrogeologic conditions, overburden strength, and premining stress conditions. Additional data was collected during 2003 and 2004 field programs. Since 2003, Bridger has had the opportunity to observe ground behavior in a series of up to 1200-1600-ft- long rectangular openings created during highwall mining. These narrow unsupported openings remained stable in the short term in large areas but the overburden subsided locally in the long-term depending on geologic and panel layout designs. These localized subsidence events allowed an examination of in-situ coal strength based on back analyses of stress. The unextracted highwall areas near Ramp 17 provided an ideal location to access the underground reserves using a 6-entry set of mains. The existing north-south oriented longwall layout for the Bridger Coal was selected by Bridger to maximize resource recovery from the D41 reserves while considering operational and geotechnical constraints. At 45-degrees deviation from preexisting joints and mild horizontal stress field, this orientation was considered beneficial for overall stability while using both sets of joints for facilitating the caving process. The present layout utilizes pillars on 80- to 90- by 200-ft centers, 17-ft entry spans and 750-ft wide longwall panels (Figure 1). Gate pillars are on wide spacings and are intended to act as abutment-abutment pillars to limit strata deformation over the gateroads during longwall mining.

Jan 1, 2008

By Greg Wieland

Deep sewer tunnels are required to meet future growth demands of the City of Austin?s down-town redevelopment. The tunnel is 18,000 ft long and varies in finished diameter from 54 inches to 96 inches. The tunnel crosses under Austin?s Town Lake three times and there are four main work shaft sites. Geology, groundwater, foundations, downtown redevelopment, and an active, healthy community put significant constraints on the design. This paper discusses a major underground project for downtown Austin and discusses the risk considerations and the opportunities the design team took toward optimizing the project design for the construction phase.

Jan 1, 2008

By Rafael C. Castro

As part of its risk management plan, the South Central Connecticut Regional Water Authority (RWA) is assessing the condition of its system of raw water conveyance tunnels and connecting pipelines. In 2006, the RWA inspected one of the system?s main tunnels, a 4-mi, 1950s-era tunnel that had not been inspected since its construction. The inspection team prepared extensively for the unknown conditions in the tunnel, and the inspection was completed safely and successfully. This paper describes the team?s pre-entry preparations, dewatering and ventilation efforts, surface-to-tunnel communication, access, physical inspection of the tunnel, and the lessons learned throughout the process. Additionally, this paper will preview planning for the subsequent inspections.

Jan 1, 2008