Search

This paper concerns the problem of designing standard artificial tunnels for rock boulder protection. The proposed approach consists in uncoupling the problem of the dynamic response of the granular dissipative soil cushion placed on the top of artificial tunnels from the dynamic response of the reinforced concrete structure underneath. An already conceived elasto-viscoplastic constitutive model capable of simulating the penetration process of the boulder within the soil stratum and reproducing the force acting on the boulder is briefly described. Its simplified one-dimensional formulation is outlined. A modified version of the model, taking into account large displacements occurring when either impacts on loose granular soils or high energetic content impacts on dense sand strata are considered, is also introduced. To validate the approach, some in situ test results are numerically simulated. A simplified numerical approach is proposed for obtaining the evolution with time of both impact force and boulder penetration, bypassing the use of the rheological model. This goal is achieved by introducing some abaci obtained numerically with reference to an ideal dense sand soil stratum of reference. DOI: 10.1061/(ASCE)GT.1943-5606.0000363 CE Database subject headings: Sand, Soil type; Tunnels; Viscoplasticity; Numerical models; Granular media. Author keywords: Impacts; Sands; Artificial tunnels; Viscoplasticity; Numerical modeling.

This paper presents the results of a comprehensive research study to determine the potential causes for an inordinate distress developed on a shotcrete liner material of a tunnel located near Dallas, TX. This tunnel was originally founded on a limestone material. Distress locations were identified where possible delamination of shotcrete layer and moisture leaks were either suspected or noticed. As a part of the research, rock cores and white powderlike substance behind the liner were collected around the distressed locations, and these cores and powder material were subjected to chemical, mineralogical, and engineering tests to understand the potential causes of this distress. Mineralogical tests, in particular, X-ray powder diffraction analysis on a powder material and gel-like substances collected on the liner, showed the presence of anhydrite, gypsum, and ettringite traces. High amounts of sulfate measurements in chemical and energy dispersive X-ray spectroscopy studies also showed that both gypsum and ettringite formations were possible in and around the limestone material. Upon hydration, mineral expansion of ettringite and anhydrite led to heaving and subsequent cracking of the adjacent shotcrete layer. Engineering characterization tests including unconfined compression strength (UCS), indirect tensile strength (ITS), and triaxial tests on rock cores embedded with a powder type sulfate material revealed that low strength cores were obtained near high distress zones and high strength cores were collected at low distress zones. The UCS values ranged from 6.2 (high distress) to 13.8 MPa (low distress) whereas the ITS values of the cores varied from 0.5 to 1.1 MPa for the same distress locations. This indicates the potential loss of strength of these rock materials from the presence of gypsum material in them. Possible methods to mitigate this heaving problem behind the liner are also discussed. DOI: 10.1061/(ASCE)MT.1943-5533.0000087 CE Database subject headings: Sulfates; Tunnels; Shotcrete; Gypsum; Limestone; Rocks; Differential settlement. Author keywords: Sulfate heaving; Tunnels; Shotcrete; Ettringite; Gypsum; Limestone; Rock testing.

A probabilistic analysis of a shallow circular tunnel driven by a pressurized shield in a frictional and/or cohesive soil is presented. Both the ultimate limit state (ULS) and serviceability limit state (SLS) are considered in the analysis. Two deterministic models based on numerical simulations are used. The first one computes the tunnel collapse pressure and the second one calculates the maximal settlement due to the applied face pressure. The response surface methodology is utilized for the assessment of the Hasofer-Lind reliability index for both limit states. Only the soil shear strength parameters are considered as random variables while studying the ULS. However, for the SLS, both the shear strength parameters and Young's modulus of the soil are considered as random variables. For ULS, the assumption of uncorrelated variables was found conservative in comparison to the one of negatively correlated parameters. For both ULS and SLS, the assumption of nonnormal distribution for the random variables has almost no effect on the reliability index for the practical range of values of the applied pressure. Finally, it was found that the system reliability depends on both limit states. Notice however that the contribution of ULS to the system reliability was not significant. Thus, SLS can be used alone for the assessment of the tunnel reliability. DOI: 10.1061/(ASCE)GT.1943-5606.0000060 CE Database subject headings: Shields, tunneling; Settlement; Serviceability; Ultimate loads; Limit states; System reliability.

Underground tunnels are considered to be a vital infrastructure component in most cities around the world. Careful planning is always necessary to ensure minimum impact on nearby surface and subsurface structures. This study describes the experimental investigation carried out to examine the effect of existing piles installed in cohesive soil and extended to bedrock on the circumferential stresses developing in a newly constructed tunnel supported by a flexible lining system. A small scale testing facility was designed and built to simulate the process of tunnel excavation and lining installation in the close vicinity of preinstalled model piles. Lining stresses were measured for different separation distances between the lining and the existing piles Consistent decrease in the lining load was observed when the piles are located within a distance of one tunnel diameter from the tunnel. The results presented in this study indicated that measuring the lining response near existing pile foundations may be used to evaluate the extent of the interaction between the lining and the surrounding piles. DOI: 10.1061/(ASCE)GT.1943-5606.0000004 CE Database subject headings: Tunneling; Piles; Soil-structure interaction; Cohesive soils.

Incidents may arise in road tunnels, in particular at the tunnel entrance and exit. Investigation conducted in the road tunnels in the provinces of Guizhou and Yunnan in China showed that the concrete pavement surface skid resistance decreased rapidly inside the tunnels and was significantly different from that outside the tunnels. Pavement surface skid resistance is one of the most important factors that affect travel safety, in particular wet weather skidding accidents. Countermeasures are necessary to enhance the skid resistance on concrete pavements in tunnels. The writers made an effort to investigate possible pavement surfaces to provide long- lasting skid resistance, including porous concrete surface and open graded friction course (OGFC) surface. Porous concrete was paved directly on the regular concrete pavement and OGFC was paved on the existing surface of concrete pavement to provide sufficient skid resistance. Accelerated abrasion devices have been developed to evaluate the skid resistances of the porous concrete and OGFC, respectively. Regular asphalt materials will bum easily and emit toxic gas in fire, which may reduce the survival rate for tunnel users involved in fire accidents. Fire-retardant asphalt has been developed to reduce the tendency of asphalt materials to burn and reduce emission. CE Database subject headings: Tunnels; Skid resistance; Concrete pavements; Porous materials; Fire resistance.

An exact analysis for three-dimensional dynamic interaction of monochromatic seismic plane waves with two lined circular parallel tunnels within a boundless fluid-saturated porous elastic medium is presented. The novel features of Biot dynamic theory of poroelasticity along with the appropriate wave field expansions, the pertinent boundary conditions, and the translational addition theorems for cylindrical wave functions are employed to obtain a closed-form solution in the form of infinite series. The analytical results are illustrated with numerical examples in which two identical tunnels, lined with concrete and embedded within water- saturated soils of distinct frame properties (i.e., soft or stiff soils), are insonified by plane fast compressional or shear waves at end-on incidence. The basic dynamic field quantities such as the hoop and axial stress amplitudes are evaluated and discussed for representative values of the parameters characterizing the system. The effects of formation material type, angle of incidence, incident wave frequency, and the proximity of the two tunnels on the liner stresses are examined. Particular attention is paid to the influence of bonding and drainage conditions at the liner/soil interface on the dynamic stress concentrations. Limiting cases are considered and good agreement with the solutions available in the literature is obtained. CE Database subject headings: Stress; Tunnels; Saturated soils; Three-dimensional models.

Cavitation induced flow instabilities are of interest in numerous applications. Experimental and numerical investigations of this phenomenon are taking place at several institutions around the world. Although there is qualitative agreement among the numerous recent papers on the subject, there is a lack of agreement with regard to important details, such as the spectral content of unsteady lift oscillations. This paper summarizes observations of a cavitating NACA0015 foil in three different tunnels that revealed remarkably different cavity shedding appearances and behaviors. Some of the differences were attributed to system instabilities. However, in addition to a different cavitation behavior attributed to system instabilities, it was found that differences in gas content could significantly alter the lift spectrum of a cavitating foil. For a certain range of the composite parameter [sigma]-/2[alpha] near 4, the dominant frequency appears to double when the gas content is reduced by a half. It is also argued that surface effects can have a significant influence on fully wetted time during cavity shedding. Normally, surface effects are assumed to play an important role in the initial inception of a fully wetted hydrofoil with gas content being the primary factor governing developed cavitation behavior However, the repetitive nature of the process implies that each shedding cycle is an individual inception process. Hence, the unexpected role of surface effects in partially cavitating hydrofoils. The conclusions reached have important ramifications concerning numerical code verification that is a topic of major concern. [DOI: 10.1115/1.2842146]

Critical for the seismic safety of immersed tunnels is the magnitude of deformations developing in the segment joints, as a result of the combined longitudinal and lateral vibrations. Analysis and design against such vibrations is the main focus of this paper, with reference to a proposed 70 m-deep immersed tunnel in a highly seismic region, in Greece. The multisegment tunnel is modeled as a beam connected to the ground through properly calibrated interaction springs, dashpots, and sliders. Actual records of significant directivity-affected ground motions, downscaled to 0.24 g peak acceleration, form the basis of the basement excitation. Free-field acceleration time histories are computed from these records through one-dimensional wave propagation equivalent-linear and nonlinear analyses of parametrically different soil profiles along the tunnel; they are then applied as excitation at the support of the springs, with a suitable time lag to conservatively approximate wave passage effects. The joints between the tunnel segments are modeled realistically with special nonlinear hyperelastic elements, while their longitudinal prestressing due to the great (7 bar) water pressure is also considered. Nonlinear dynamic transient analysis of the tunnel is performed without ignoring the inertia of the thick-walled tunnel, and the influence of segment length and joint properties is investigated parametrically. It is shown that despite ground excitation with acceleration levels exceeding 0.50 g and velocity of about 80 cm/s at the base of the tunnel, net tension and excessive compression between the segments can be avoided with a suitable design of joint gaskets and a selection of relatively small segment lengths. Although this research was prompted by the needs of a specific project, the dynamic analysis methods, the proposed design concepts, and many of the conclusions of the study are sufficiently general and may apply in other immersed tunneling projects. CE Database subject headings: Tunnels; Earthquakes; Dynamic analysis; Soil-structure interaction; Vibration; Nonlinear response; Seismic effects.

Experiences show that the design of overlay mortars is a complicated matter as far as long-term durability and dimensional stability are concerned. In many cases, applied mortars crack or delaminate a few years after application. The same is true for passive fire protection mortars (PFP mortars). The mortar must remain crack free and must not delaminate during the planned service life, that means the fire protection requirements must be combined with the durability requirements. In this paper, an approach based on a numerical model is used to forecast the long-term behavior of PFP mortars. By means of this model, the time-dependent humidity, temperature, stress, and strain distributions, as well as the crack formation can be calculated in a realistic way. The minimal adhesive strength between overlay and substrate which is necessary to prevent delamination during the planned service life has been calculated. Material properties and climatic boundary conditions have been taken into account. The results allow the tailored optimization of PFP mortars. DOI: 10.1061/(ASCE)0899-1561(2007)19:6(484) CE Database subject headings: Concrete durability; Fire protection; Mortars; Numerical models; Tunnel construction.

An assessment of the structural performance of concrete tunnel linings under tire load is presented for the Lainzer Tunnel, a shallow tunnel recently constructed in Austria. Prior to the installation of the concrete lining at this tunnel, large-scale temperature experiments were conducted, revealing almost no reduction of the lining thickness in consequence of spalling for the employed lining concrete, reinforced by polypropylene fibers. In the absence of spalling, dehydration of concrete under high temperatures is the safety-determining process. Within the thermochemomechanical material model employed for the tunnel-safety assessment presented in this paper, dehydration is described by the decrease of the hydration extent, resulting in the reduction of both stiffness (thermal damage) and strength (thermal decohesion). The distribution of the hydration extent is determined by means of a thermochemical analysis. The obtained results serve as input for the subsequent chemomechanical analysis, providing insight into the deformation state of the ground-lining compound structure and the stress state in the lining. As a function of the stress state, a level of loading L is introduced, with L=0 for the unloaded material and L = 100% for stress states reaching the compressive strength of concrete. During fire exposure the size of L increases because of increased loading by thermal expansion, on the other hand, and because of thermal decohesion resulting in a reduction of the compressive strength, on the other hand. The difference between 100% and L; represents the remaining load-carrying capacity of the lining, giving access to the safety of the tunnel for the chosen fire-accident scenario. DOI: 10.1061/(ASCE)0733-9445(2006) 132:6(961) CE Database subject headings: Tunnels; Fires: Concrete; Loads; Linings: Safety.

The authors of this paper present the results of a study concerned with the assessment of the vibrational impact induced by the passage of commuter trains running in a tunnel placed underground the city of Rome. Since the railway line is not yet operational, it was not possible to make a direct measurement of the ground vibrations induced by the railway traffic and the only way to make predictions was by means of numerical simulations. The numerical model developed for the analyses was calibrated using the results of a vibration measurement campaign purposely performed at the site using as a vibration source a sinusoidal vibration exciter operating in a frequency-controlled mode. The problem of modeling the vibrational impact induced by the passage of a train moving in a tunnel is rather complex because it requires the solution of a boundary value problem of three-dimensional elastodynamics in a generally heterogeneous, nonsimply connected continuum with a moving source. The subject is further complicated by the difficulties of modeling the source mechanism, which constitutes itself a challenge even in the case of railway lines running at the surface. At last, the assessment of the vibrational impact at a receiver placed inside a building (e.g., a human individual or a sensitive instrument) requires an evaluation of the role played by the structure in modifying the computed free-field ground motion. So far, few attempts have been made to model the whole vibration chain (from the source to the receiver) of railway-induced ground vibrations, with results that have been only moderately successful. The numerical simulations performed in this study were made by using a simplified numerical model aimed to capture the essence of the physical phenomena involved in the above vibration chain including the influence of the structural response as well as the dependence of the predicted vibration spectra on the train speed. [DOI: 10.1115/1.2013300] Keywords: Ground-Borne Vibrations, Railways, Trains, Tunnels, Vibration Modeling, Moving Train

The Tymfristos tunnel, a 1,365 m long road tunnel with an 11 m section diameter, was excavated through the highly tectonized, low strength Flysch formation of central Greece. About 1 year after the completion of the excavation in 1995, convergence of up to 20% followed by failure of the support system was recorded. A 501 m long segment, in which the failure occurred, was reexcavated based on a more detailed study of the ground conditions; however, this second phase was also followed by an up to 6% convergence. The detailed geodetic study of the three-dimensional kinematics of the support shell in relation time, ring closure delays, and support measures reveals an unusual time-history of convergence occasionally continuing even after the ring closure and a nonuniform distortion of the lining. Furthermore, uncontrolled deformation of certain 'weak' sections propagated bidirectionally to adjacent, previously stabilized sections producing a 'chain effect,' responsible for destabilization and resumed convergence of long (~ 90 m) segments. CE Database subject headings: Convergence: Deformation analysis; Tunnels: Failures: Greece.

According to the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) report in 1982, radiation from radon contributes about 50% of all natural radiation sources to the public. The situation is worse in Hong Kong where large area is granitic containing larger amount of uranium when compared to the global mean. Radon level can therefore be on the high side during tunneling especially where poor ventilation is envisaged. This article includes realistic field study of radon in tunnel under construction. A maximum concentration of over 30,000 Bq/[m.sup.3] was recorded (1 Becquerels per cubic meter is equivalent to 0.027 pico Curies/L). Radon concentration in tunnel environment is found to be related to groundwater ingress, ventilation provision and geology. A review of the current statutory control in Hong Kong is done as well as its comparison with other countries' practices. In fact, the situation can be improved through education, adopting control legislation and more specifically, having a suggested radon management plan in every tunnel drilling project. CE Database subject headings: Radon: Tunnels: Drilling: Ventilation.

A numerical method for the analysis of tunnel-wall interference effects in forced-oscillation testing is presented. The method is based on the wall-pressure signature concept and utilizes the computed wall-pressure distributions. The induced wall pressure field is computed by using an unsteady three-dimensional full Navier--Stokes solver for a 70-deg pitching delta wing in a wind tunnel. To validate the code, the computed static results are shown to have good agreement with the experimental data of Wentz in lift and drag coefficients. On the other hand, the computed static and dynamic normal force coefficients are, in general, higher than those in a second set of data. However, the predicted hysteresis curves of normal force coefficient in large-amplitude-oscillation testing agree reasonably well with this second set of data. The computed unsteady pressures on the tunnel walls and floor are used to generate the interference flowfield that is analyzed for the upwash and blockage corrections. The corrected results are shown to agree well, in the slope and magnitude of hysteresis loops, with the computed results in free-air conditions. It is also shown that the hysteresis in upwash and blockage corrections increases with the reduced frequency.

Estimates of ground deformations and liner stresses in a tunnel are usually obtained from empirical correlations or from past experience on similar tunnels. These correlations account for only a few of the significant factors, and extrapolation to other cases is questionable because similitude conditions are not generally fulfilled. In this paper, complete analytical solutions for a shallow tunnel in saturated ground are obtained. Two different drainage conditions have been considered: full drainage at the ground-liner interface, and no drainage. The solutions cover different construction processes and soil conditions: (1) dry ground; (2) saturated ground with and without air pressure; (3) with and without a gap between the ground and the liner; and (4) applicability for short term analysis (i.e., undrained excavation and liner installation) and for long term analysis. Since the ground and the liner are assumed to behave elastically, the solutions obtained are restricted to cases where ground deformations are small, such as stiff clays and rocks, or when the excavation method prevents large deformations of the ground.

This article brings out background information and evidence of a forensic investigation into a massive sinkhole accident in Georgia resulting in two fatalities. Data indicate that soil erosion coupled with a failure in the sewer tunnel built on top of fill soils are the causes of the accident.

A large number of centrifuge model tests for simulating the shield construction process in dry sand was carried out by using a newly developed 100 mm diameter miniature shield tunnel. Different construction processes were modeled by three series of tests. A 'buried tube test' was conducted to measure the lining stress under a centrifugal acceleration, a 'tail void test' simulated the process of tail void formation only, and a 'shield test' dealt with the complete process of shield construction. Lining stresses, transverse and longitudinal surface settlements, and earth pressures around the tunnel were simultaneously measured during advancement of the shield at a centrifugal acceleration of 25g. The lining stress at the crown elevation was well predicted by Terzaghi's loosening earth pressure. From the comparison with the recent field measurements and the comparative results of three series of tests, it was confirmed that the shield construction process was successfully simulated in a centrifuge. An experimental formula for estimating the surface settlement above the shield was deduced by a function of tail void thickness and cover-to-diameter ratio.

The south cut and cover of the Confignon tunnel in Geneva, Switzerland, lies on deposits of clay and clayey silt of high and varying compressibility. Without improvement of the foundation, settlements under the final loads of the cover are unacceptable for the project. The improvement of the foundation was achieved by a preload drain system. Monitoring settlements under the fill loads and heave at fill removal indicate: (1) maximum settlement values of 34 cm (340 mm); (2) reduction of the compressibility of the foundation to one-third of its original value in the preloading process; (3) values of the in-situ coefficient of consolidation 1.5-2 times larger than the design values derived from the oedometer test results; and (4) a computed settlement 1.5 times the monitored settlement at the location of the maximum settlement. Monitoring the settlements of the concrete structure under the cover loads indicates: (1) a present maximum settlement of the order of 8 cm (80 mm); and (2) a predicted maximum settlement over the 80-year life period of the project on the order of 12 cm (120 mm) with low differential settlements.

The Inland Feeder designed to increase the amount of state-produced water for Southern California comprises of the Arrowhead East and Arrowhead West Tunnels. The tunnels incorporate structural features like impermeable lining, unique seismic sections and extensive probing and grouting to account for earthquakes and a ground-water monitoring program with 100 monitoring sites. The use of thick-walled steel pipes in fault zones serves a means of protection for the tunnel-workers during earthquakes.

The construction of tunnels at the complex Fort Point Channel I-90 portion of Boston's Central Artery Project involves tunnel jacking, deep soil mixing and outsized immersed tube tunnels by the engineers and contractors. Contacts worth over a billion dollars have been awarded for the purpose. The design and construction of Fort Point Channel faces challenges regarding the use of new techniques and weak clay soils

Reinforced rock arch design works on the basis of utilizing a rock's inherent properties to make it work as an arch. The advantages of this tunnel construction method includes reduced construction costs, increased flexibility, improved safety and minimized labor and materials. The final structure consists of the rock mass interacting with the reinforced rock arch to form the tunnel. This interaction stabilizes the structure and limits deformations toward the tunnel opening. Engineers should be able to adapt to specific site conditions to ensure the viability of constructing rock arches.

The Singapore Ministry of Environment was forced to construct a new sewer tunnel as close as possible to the mass transit tunnels since a deeper excavation would significantly increase operational costs. The ministry decided that an underground chamber for the sewer beneath the transit tunnel alignment should be constructed early on the basis of geotechnical studies and risk assessments. The chamber would be built before the rail project so that the tunnel-boring machine for the sewer can pass 2.5 meters below the finished rail tunnels.

Constructors encountered petroleum-hydrocarbon-saturated sandstone during the design phase of the Hilltop Interceptor tunnel project in Cleveland, OH. Engineers from Parsons Brinckerhoff Ohio Inc. used high-density polyethylene as lining material for the cast-in-place concrete shaft to ensure project health and safety and prevent oil seepage into the shaft after completion. Waste material certified not to contain oil was used as fill material while those containing oil were disposed in landfills or treated before discharge to Ohio's sewage collection system.

The Boston Central Artery/Tunnel (CA/T) project aims to decongest Boston's roads and improve its surrounding areas. The construction of an immersed tube tunnel in Boston Harbor, which constitutes a part of the CA/T project, poses many challenges to its engineers and designers. The tunnel installation involves steel fabrication, trench excavations, blasting and dredge material disposal. Construction management takes into consideration the project's effects on Boston Harbor and time management is used to minimize disruption of the harbor's activities.

The A86 Duplex is a 10 km long bilevel tunnel that can accommodate up to three lanes of traffic in each direction. The tunnel will complete the Paris ring road by 2010 and was designed to accommodate only passenger cars and other light vehicles. It will be constructed of reinforced-concrete segments with 30 mm thick walls and will have escape passages located every 200 m.

Investigators from the National Transportation Safety Board (NTSB) concluded that the use of an epoxy anchor adhesive was the cause of the collapse of 10 ceiling panels in the D portal connecting Interstate 90 in Boston to the Ted Williams Tunnel, which is part of the Big Dig project. The NTSB raised issues on how the epoxy came to be used and why inspections were not carried out even after signs of displacement or 'creep'.

The high-performance of tunnel boring machines used by Jay Dee Contractors increased the construction speed of Little Calumet Leg, the final part of Chicago Tunnel and Reservoir Project (TARP). The constructional details of tunnel are presented along with the specifications of the tunnel boring machine.

A 6,280m long Hai Van Pass of Vietnam the longest highway tunnel in Southeast Asia, which is opened on June 5, is discussed. The tunnel has a cross sectional area of 73meter square and will carry daily traffic.

King County issued bid application deadlines in September 2005 for the construction of first of three tunnel sections that form Brightwater Wastewater Treatment Plant (WWTP). The three tunnels will measure 13 miles and is expected to start construction in late 2006.

The construction on a pair of tunnels that would transfer water between two sources as part of a larger project to provide high-quality drinking water to more than 750000 residents in the area of Vancouver, British Columbia is described. The tunneling project would begin with a 185 m deep vertical shaft at the Seymour end.

The Massachusetts Water Resources Authority (MWRA) proposes to build a tunnel to collect excess sewage from the Boston waterways. The proposal is intended to eliminate combined sewer overflows at a number of poplar beaches located along Boston's North Dorchester Bay.

The Channel Tunnel Rail Link (CTRL), connecting the Channel Tunnel with London, will significantly decrease travel times between London and continental Europe when it is completed in 2007. In designing the project's tunnels, engineers have made advances in such areas as the large-scale use of fiber reinforced precast-concrete linings and the design of shotcrete linings.

This article discusses the restoration plans for the Peruvian andes following destruction of the hydroelectric power plant and debris collection from the floods. Design and construction of a high-profile tunnel from the right side of the valley through rock face into the river and then through rock on the opposite side of the valley to a reception shaft is described.

Buckling of thin cylindrical shell liners used for the stabilization of soft ground tunnels is treated as the buckling of an elastic ring restrained radially and tangentially by an infinite surrounding elastic medium. Stiffness components for the elastic medium are derived and used to provide various levels of approximation for the elastic critical loads and associated modes of the liner when subject to overburden pressure loading. For most practical tunnel liners, elastic buckling is found to occur in modes having relatively short circumferential wavelengths. In these circumstances an approximation introduced into the critical pressure analysis allows both the lowest critical pressure and its associated mode shape to be represented explicitly in terms of a single 'soft ground tunnel buckling parameter'; this single composite parameter encapsulates all the relevant ground and liner geometric and material properties. It is this closed-form analytical representation of elastic critical buckling that provides a particularly convenient basis for predicting elastic-plastic failure. When imperfections are introduced, liner collapse and the various forms of ground failure can be modeled by methods analogous to the Ayrton-Perry expression for columns. Two generalized imperfection parameters emerge: one for liner collapse and the other for each of three possible, soft ground, failure modes. It is suggested that the analytical simplicity of the approach should make it an attractive alternative basis for at least the initial, rational, design of soft ground tunnel liners.

The largest diameter tunnel in North America is planned to be built by the Metropolitan Transportation Authority of Los Angeles County in order to provide a freeway to the commuters. Details of the two tunneling techniques intended to be used for the proposed project are presented.

The world's largest tunnel-boring machine will be used by Ontario Power Generation, Toronto, for tunnel construction on the Niagara River. Details of the tunnel are presented. The tunnel will convey water to the Sir Adam Beck power generating complex in Ontario.

An analysis of how knowledge and technical expertise of small engineering firms helped the construction of the $14-billion Boston's Central Artery/Tunnel, also called the Big Dig, is presented. The small firms provided technical expertise on urban design, architecture, and traffic management to large engineering firms.

The King County Department of Metropolitan Services is constructing a soft-ground tunnel to divert wastewater for secondary treatment and store storm-water overflows in the West Seattle drainage basin, WA. Site constraints, geology and construction issues affected the design of the 10,200-foot project, which will divert dry weather sanitary flow and store excess flow during wet weather at the Alki plant, Seattle.

Tunneling operations for the North Huron/Rouge Valley Wastewater Control project in Wayne County, MI, revealed a range of soil conditions that will make progress difficult. The project's contractor, joint venture Kajima/C.J. Rogers, adopted a method that combined an automated tunnel-boring machine (TBM) with a manual TBM for the pipe-laying process. The wastewater facility is the first phase of a three-part sewer project for Wayne County, MI, and will connect far-flung areas like Dearborn to Detroit's sewage facilities.

The Central Artery/Tunnel in Boston, MA, an $8 billion project which is being handled by four companies, was the topic discussed during the Geo-Institute conference. The project designers showed that plans are carefully laid to balance the construction cost without putting the project at risk. Several problems regarding the project such as constructing the tunnel in an urbanized area and construction site's stability were raised and possible solutions were presented. Other related topics such as geophysics and spatial analysis in soil and landslides were also dealt with in the conference.