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The Second Avenue Subway is currently under construction in Manhattan, New York. Spanning seven city blocks, the cut-and-cover station at 96th Street is the largest station in Phase 1. The station excavation is up to 68 feet deep and is typically within 20 feet of adjacent buildings. The station straddles areas of rock and deep soil at its invert and requires various forms of ground support, including both temporary and permanent secant pile and slurry walls. Construction was undertaken in a dense urban environment, adjacent to fragile buildings, with significant underground utility and traffic maintenance restrictions. Excavation and construction of the permanent earth support was recently successfully completed. This paper reviews the design and construction methodology for the ground support systems adopted and discusses the interfacing and construction challenges faced in a highly constrained environment from the perspectives of both the designer and contractor.

A rectangular starter trench measuring 220 feet long by 23 feet wide and a 24-foot diameter, 12-sided receiving shaft were built in order to accommodate launching and removal, respectively, of an earth pressure balance (EPB) tunnel boring machine (TBM) which was used to construct a subaqueous water supply tunnel in New York City. For the TBM starter trench located in Staten Island, the 4-foot wide slurry walls were excavated with a clam shell and a hydromill to a depth of approximately 90 feet through fill and glacial soils and into competent rock at the western portion of the excavation, and to 107 feet into decomposed bedrock at the eastern portion. During slurry trench excavation, the work was closely monitored by performing time-controlled slurry tests and examining muck conditions from a slurry separation plant. Also, vertical and horizontal deviations of the slurry trenches, rebar cage placement, and the concrete pour were closely monitored and inspected to maintain construction within the design tolerances. For the TBM receiving shaft in Brooklyn, the 3-foot wide slurry walls were excavated to a depth of approximately 155 feet mostly with a hydromill. Difficult ground conditions due to uncontrolled fill including wood timber and concrete debris, and glacial sand with boulders were overcome with intermittent use of a clam shell and large chisel. The rebar cages of the primary panels were fabricated in a “concave up” shape and the secondary panels were constructed in a rectangular shape. Together they formed the circular shaft shape. Due to the slurry wall depth, three sections of the rebar cages were spliced while inserting into the slurry trench. The TBM break-in and break-out portion of the slurry walls were reinforced with fiber-glass rebar.

Tuttle Creek Dam in Manhattan, Kansas was found to be seismically deficient. Cement-bentonite slurry walls were used to remediate the dam. We use the EFFC DFI Carbon Calculator to calculate the carbon footprint of the cement- bentonite slurry walls, as well as the carbon footprint of an alternative remediation option, stone columns. The cement-bentonite slurry walls resulted in a GWP 100 of 71,000 tonnes CO2 equivalent, while the stone columns resulted in a GWP 100 of 3,900 tonnes CO2 equivalent, a significant difference even when considering the uncertainties in life cycle modeling. The Carbon Calculator is a simple tool for quantifying the carbon footprint of different geotechnical engineering techniques.

This investigation was conducted to evaluate the beneficial reuse of post-consumer waste insulation materials in drilling and slurry applications. In particular, waste fibrous insulation was used to replace bentonite in slurry mixtures. Three civil engineering applications were considered for potential insulation waste reuse: drilled shaft/slurry trench construction, directional drilling, and vertical drilling. Effectiveness of slurries was assessed using conventional tests such as Marsh funnel viscosity, density, and filtrate loss. Filter cake thickness and filter cake permeability also were determined. Test results indicated that insulation materials could be used to replace up to 48% of bentonite in drilled shaft/slurry trench applications, up to 36% of bentonite in directional drilling applications, and up to 47% of bentonite in vertical drilling applications while maintaining acceptable engineering properties. Incorporation of waste insulation material in bentonite slurry mixtures is a viable beneficial reuse alternative.

The Cone Penetration Test (CPT) is widely used for classifying soils and assigning soil properties to the subsurface because it is robust and can be used to quickly collect continuous data with depth. During and subsequent to the construction of a very deep soil-bentonite (SB) slurry trench cut-off wall in Mayfield NSW, Australia, the CPT was used to check the continuity and quality of the SB backfill material. The numerous CPT profiles conducted in the Mayfield wall provided a unique research opportunity for examining how shear strength and effective stress vary with depth. A method is proposed to estimate the undrained shear strength of the Mayfield Wall from the CPT combined with some vane shear data. The results support previous studies that show that the shear strength and the effective stress distributions in SB slurry trench cutoff walls are less than would be expected from a geostatic stress distribution. While there is some increase in shear strength with depth, these data show the increase is modest and consistent with the less than geostatic stresses. In addition, the authors recommend a general procedure for shear strength and horizontal stress estimation using CPT data in any SB slurry trench application.

This paper presents a case study of a deep soil-cement-bentonite (SCB) slurry trench cutoff wall constructed outside of Smithland, KY, in 2010. Installed to a maximum depth of 56 m, this cutoff wall is the deepest known seepage barrier installed using continuous trenching. The wall was installed around the perimeter of a deep excavation to reduce long-term dewatering costs associated with construction of a hydroelectric power plant adjacent to the Ohio River. After wall construction, a dewatering system was installed inside the area enclosed by the wall to facilitate the deep excavation. Preconstruction design and construction details are presented along with the results of a post-construction assessment of the hydraulic conductivity ( k ) of the wall. Steady-state groundwater flow measurements from the dewatering system coupled with information on the wall thickness and water levels inside and outside of the wall were used to obtain a large-scale estimate of the in situ k of the wall. The in situ k was compared with laboratory k values measured for specimens prepared from grab samples of the as-mixed SCB backfill. Comparisons also were made to the target (design) k and the expected field mixed backfill k established during a preconstruction bench-scale study. The comparisons revealed that the in situ k is approximately one order of magnitude less than the design k and approximately equal to the average laboratory k measured from grab samples and the expected k from the results of the bench-scale study.

This paper reports a reduced-scale shake table test investigating the seismic response of a slurry wall. Soil-cement-bentonite (SCB), a common type of slurry wall, was evaluated in this research. A section of a slurry wall of 1.68 m long, 0.20 m wide, and 1.60 m tall was constructed and tested on a one-dimensional shake table. A 1.50 m × 1.87 m × 1.80 m box was anchored on the shake table and contained the slurry wall and the sandy soil that was compacted on both sides of the wall. The slurry wall and the confining soil were instrumented with accelerometers, linear variable differential transformers (LVDT), linear potentiometers, and dynamic soil stress gauges to respectively record the accelerations, vertical and horizontal deformations of the wall, and transient dynamic soil pressures on the wall during the simulated seismic excitations. Scaled 1989 Loma Prieta earthquake motions were simulated by the shake table. The testing was an improvement over previous testing by the authors and implemented flexible boundaries and dynamic scaling laws. The shake table tests provided a preliminary understanding of the seismic performances of the SCB slurry wall in levees and earth dams.

Diaphragm wall is commonly used as retaining structure in foundations of subway stations. The stability of slurry trench excavated during construction becomes a major concern. Field cases with the geology that a sand layer of low stability is sandwiched between two relatively stronger clays are often encountered. Because layers above and beneath are impermeable clays, confined water pressure may exist. The local stability in terms of this special geology needs to be carefully investigated. In this paper, the problem is foremost simplified to be modeled as a sand layer compressed between two rigid plates. Hyperbolic partial differential equations are established assuming the sand layer, which is rigid plastic conforming to Mohr-Coulomb yield criteria, is a limit state. The equations are then solved to obtain the theoretical solution of stress distribution on the trench surface so that a simplified formula to compute factor of safety of local stability is derived. Finally, a case history is presented and the validation of the formula is verified by numerical analysis. The method proposed by this paper successfully predicts the failure pattern of the trench face and can be applied in practice.

Pipe-jacking is widely used in municipal pipeline installation, and accurate calculation of jacking force is essential for construction design. Various formulas exist to calculate jacking force, which greatly differ in results. Most formulas are based on classical soil mechanics theories and some simplified assumptions that consider friction coefficient between soil and pipes as a fixed value or neglect the effect of slurry thixotropic. Considering the interaction of soil layers, thixotropic slurry and tube wall, friction is consistently changeable during the jacking process; thus, these formulas and theories cannot meet construction demands. This research is based on the Changchun Yitong River drainage pipelines reconstruction project which used slurry balance pipe-jacking machines to handle mudstone geological conditions. The authors used MATLAB to calculate, analyze and compare jacking force with field measured data. Finally, calculation formulas of jacking force and friction force were derived which took mudstone formation and interaction of soil layers, thixotropic slurry and tube wall fully into consideration

Lower Carno Reservoir is situated 3 km north of Ebbw Vale, in Wales. The 27-m-high dam, completed in 1911, has a central puddle clay core supported by shoulders of clay and stony material. The core is extended into the foundation to form a narrow cut-off trench up to 30 m deep in the abutments and 10 m deep in the central section. The dam has had a history of leakage and a succession of remedial works has been carried out. In January 2005 operations staff, who visit the reservoir on every working day, notified the Reservoir Engineer of increased flows in the toe drains. After investigations to trace the source of the flows were unsuccessful and the rate of leakage increased rapidly, it was decided to empty the reservoir. Measured settlement of the wave wall beside the culvert had reached 320 mm since 1990, of which 150 mm occurred in the few days after emptying. This paper briefly describes the history of construction and leakage; environmental issues; the investigation of the dam and selection of remedial works; and the design and execution of the complex and delicate remedial works necessary to bring the structure safely back into operation, including a 40 m deep slurry wall membrane and a new grout curtain in rock. The remedial works included the following key elements - ≤ 3-D modeling of the dam and remedial works geometry ≤ Construction of a 40-m-deep slurry wall with fully automated hydraulic grab ≤ Drilling with grout flush in the embankment ≤ Use of water operated DTH hammers for drilling in rock ≤ Maxibor survey of boreholes ≤ Computerised software for the design, control, monitoring, analysis, and reporting of the grouting works ≤ Use of G.I.N. technology for rock grouting ≤ Real time control of closure criteria by means of 'Equivalent Lugeon' referencing ≤ Use of C3S stabilized, fluidified cement bentonite slurry for rock grouting ≤ Contact grouting and sealing of the draw-off culvert ≤ Lugeon testing programme in control holes for final verification.

Mixtures of clay and lime or clay and natural pozzolans are possibly some of the most ancient construction materials, and yet there is still much that we do not know about the properties of clay-binder systems. There has been an enormous amount of research on cements and also on clays, but curiously there has been little systematic research on combined cement-clay systems. This paper provides an overview of the properties of clay-cement systems in their many applications, but is focused on the cement-bentonite clay slurries used in slurry trench cut-off walls. It particularly considers areas where it is believed that more research is required; but it also briefly reviews the basic behaviour and properties of cement-bentonite systems including some of the lesser studied aspects of the materials and recent developments.

The York Durham Sewage System (YDSS) Interceptor Sewer construction spanned a total length of 5.5 km, which included a 1.4 km stretch of open cut construction and tunnelled stretch of 4.1 km, with four access shafts. Two of the tunnel access shafts were located in an environmentally sensitive area with water bearing cohesionless soils and considered as a potential geotechnical hazard for tunnel break-ins/breakouts. A combination of slurry wall and jet grouting was used to stabilize the ground and control groundwater flow at shafts #2 and #3, during break-in/break-out of the tunnel boring machine (TBM). This paper presents a case study, addressing the application of double fluid jet grouting technique to mitigate a significant geotechnical hazard at shafts #2 and #3 for the YDSS Interceptor Sewer Project.

The design of new underground subway stations in a complex urban environment will be discussed. Major topics covered will include both cut-and-cover structures and mined caverns, the factors in determining the applicability of each, and the main requirements and challenges of designing and constructing these systems in a highly constrained environment. The key determinants in the choice of the type of structure will be investigated. Loading, types of analysis utilized and constructability issues will be discussed. The discussion of cut-and-cover structures will include the use of both secant pile walls and slurry walls. The advantages, disadvantages, suitability and design considerations of each system will be examined. A key topic of discussion will be constructability issues related to these types of construction in a metropolitan area and the solutions that may be implemented. The close relationship with geotechnical data and its impact on geometry will be covered.

This paper presents the results of a field study to assess post-construction changes in the volumetric water content () of a soil-bentonite (SB) slurry trench cutoff wall. Time domain reflectometry (TDR) sensors were installed in a newly-constructed SB cutoff wall in the summer of 2008 and were used to monitor  as a function of depth within the SB backfill for approximately one year. The methods used to install the probes are described and the measured  distributions are presented and discussed. A general trend of decreasing  with time was observed at all sensor locations. Decreases in  within the portion of the wall below the water table are attributed to backfill consolidation, whereas the larger decreases in  near the top of the wall (above the water table) are likely due to a combination of backfill consolidation and backfill drying. A field sampling program is recommended to confirm the moisture profiles obtained from the TDR sensors.

The gravity-driven effluent conveyance from Seattle’s third wastewater treatment plant to a Puget Sound marine outfall required a deep-lying, 21-kilometerlong tunnel alignment. Access for tunnel boring machine launch and reception operations, as well as conveyance system functions to pump influent to the plant, necessitated the design and construction of deep shaft structures. Geologic settings at the shaft locations ranged from liquefiable alluvial valley deposits to glacially overconsolidated sequences of glacial and non-glacial deposits. This paper discusses site-specific geotechnical design considerations, including safety against uplift, seismic hazard analysis and seismic design, baseline values for boulders, the selection of suitable construction methods, and prevention of third party impacts. The final design for most deep shafts included large-diameter diaphragm wall structures constructed by slurry wall trenching. The 62-meter-deep Ballinger Way portal shaft was constructed using ground freezing technology for ground support. Construction monitoring included tracking geotechnical conditions, groundwater response, shaft deformation and subsoil temperature development at the freeze shaft location. The monitoring results provided the basis for a comparison with and the verification of design considerations, allowing a better understanding of the geological conditions and the geotechnical system behavior.

The concept of containment is often employed at existing and planned landfills, at sites contaminated with dense nonaqueous phase liquids (DNAPLs) and at sites where a physical barrier is required. A vertical cutoff wall is one of the critical elements of the containment system. This physical barrier can provide hydraulic control and prevent migration of contaminants from the area of impacts. Several types of vertical cutoff walls are currently available and include steel or plastic sheet pile walls, geomembrane walls, slurry walls, deep soil mixing type walls or grouted walls. The other components of the containment system include surface water control and capping or liners. Ideally, a properly designed, constructed and operated containment system would create a totally impervious site encapsulation. Realistically, since the design, construction and operation are performed under conditions of uncertainty, containment system performance should be measured in terms of probability. Whether the containment system is in the design phase or in operation, the reliability of the vertical barrier should be assessed. The reliability of the vertical cutoff wall is a function of several variables. These variables are associated with uncertainties and are evaluated through a probabilistic analysis. The performance function is intended as a means to evaluate a component's dependence on design and control variables. These variables are selected based on engineering design principles, historical field data collected by the authors and data published by others. Assessment of long-term reliability of steel sheet pile wall with sealant is presented and a design equation is derived based on probability and field data. Similarly, reliability of each containment system component can be evaluated. The proposed model provides a means for comparison between different technologies and at the same time allows assessment of the reliability of multi-component systems. Additionally, this model can provide important information that can be used in risk analyses.

As part of the plan to increase the capacity of the Port of Brisbane, reclamation of a total area of 235 ha is in progress. The main geotechnical issue at the site is the extremely soft material dredged from the Brisbane River and Moreton Bay shipping channels. Over part of the reclamation area, Menard Bachy was selected by the Port of Brisbane Corporation to carry out deep soft ground consolidation, using the method of Vacuum Consolidation. In 2007, a trial area of 1.5 ha was first implemented. Following successful completion of the trial, a second and larger project was begun in 2009. The new single cell area of 9.3 ha is currently under vacuum depressurization and the soil consolidation is expected to be complete by early 2011. A significant feature in the vacuum system adopted is the 15m deep soilbentonite cut-off wall incorporating a high-density polyethylene (HDPE) liner, which is required at the periphery, to isolate the vacuum areas over the depth of the permeable layers in the subsurface profile. To ensure the confinement required for the depressurization, the slurry wall and incorporated liner are joined to a surface cap HDPE liner to complete an air and water tight seal around and over the block of soil. The initial trial incorporating the deep cut-off wall was a first in Australia and was a success in terms of both outcome and execution with depressurization, under the vacuum membrane, being maintained constantly in the range of -0.80/-0.70 bars over a long period of time of 18 months. Confinement work on the current project, which is taking place over a significantly larger scale and using improved technique, is currently in progress. The ability of Soil-Bentonite slurry walls incorporating HDPE liners to perform as air-tight and water-tight barriers under high pressure differential (0.8 to 0.7 bars) and subjected to significant deformation has been tested on these large scale projects. The barrier system has proven to be effective for considerable periods of

Defect details in bored pile and drilled pier foundations are presented for multiple installation methods to a depth of 70 ft (22 m) in projects along the Texas Gulf Coast. Over 2000 bored pile and drilled pier foundations covering four projects are reviewed. For nearly five decades drilled pier soldier pile walls have been an economic alternate to the reinforced concrete slurry wall which has enjoyed wide spread popularity across the North American Continent; hence the bored pile and drilled pier foundations used to form a basement wall on a project are numerous and are each exposed to the bottom basement level as construction proceeds. The experiences of design, preparation of construction documents and construction geotechnical engineering along with exposure allow a unique assessment of the design and construction compatibility of the completed drilled piers and bored piles. One project includes the observed limitations of low strain nondestructive testing to assess the presence of soldier pile defects for 24 in. (50 cm) diameter bored piles. Bored pile and drilled pier foundation defects are complex and do not lend themselves to easy assessment by non destructive testing. Accordingly, it is concluded that defects in bored pile and drilled pier foundation construction are inherent and that control of the construction means and methods is the only rational means available to build deep foundations with manageable defects. Hidden defect factors or reduced structural factors are needed for the design of deep foundations which will limit concrete carrying capacity below column design values because of the construction limitations, but the hidden defect factor cannot be a replacement for the control of construction means and methods by rational construction geotechnical engineering.

In one of the first applications of Cutter Soil Mixing (CSM) technology in the United States, a 12 to 17.4 m (40 to 57 ft) permanent deep soil mixed wall was constructed to enable the excavation for an office building near downtown Seattle in difficult soil conditions with a high water table. Unlike conventional slurry walls and diaphragm walls that utilize concrete, soil mixing relies on mixing the soils in situ with a cement and bentonite slurry to create a soil-cement wall. Cutter Soil Mixing technology utilizes two sets of vertically mounted cutting wheels rotating about a horizontal axis to produce rectangular panels of treated soil. By overlapping the soil mix panels, a continuous rectangular wall is constructed, as opposed to circular columns created with conventional single-axis or multiple axes deep soil mixing systems. The Elliott Avenue project located just north of downtown Seattle at the base of Queen Anne Hill required permanent excavation support to depths of up to 17.4 m (57 ft) in mixed soil conditions consisting of loose sands and gravels, underlain by stiff plastic clays and very dense glacial till. Because the project is located on the water front, the groundwater table at the site was found at a depth of 0.6 m (2 ft) from construction grade. It was thus necessary to support the saturated loose sands and gravels with a robust earth retaining system. Cutter Soil Mixing (CSM) was selected as the method of choice for several reasons, namely: price and schedule relative to a concrete secant pile wall; the ability of CSM to construct a permanent, high quality cutoff wall in the dense gravels and stiff plastic clays; the capacity of the cutter mixing tool to key into the glacial till; and, the ability of CSM to produce a soil-cement material with a minimum strength of 1.38 MPa (200 psi) and a maximum permeability of 5 x 10 –6 cm/sec.

The conventional slurry trench methods of constructing low-permeability vertical barriers have been widely used, namely, soil-bentonite (SB), cement-bentonite (CB) and slag-CB. More recently, in situ mixing methods to construct vertical barriers, such as Deep Soil Mixing (DSM) and the T rench R emixing and D eep wall method (TRD) have found increased usage. The TRD method was has been widely employed in Japan for nearly 15 years but has only recently been used in the United States. The TRD method is a one-phase process that involves the simultaneous, full-depth cutting and mixing of in situ soils with additives to create, in place, a continuous soil mixed wall. A blend of cementitious materials (granulated ground blast furnace slag and Portland cement) and slurry are injected as the milling/cutting proceeds horizontally resulting in continuous vertical mixing of in situ soils with the injected materials, without creating the open trench typical of other walling methods. To date, three TRD projects have been completed in the United States. The focus of this paper is the most recent project completed on the Herbert Hoover Dike (HHD). Other projects include 1) the first TRD project in the United States where the method was used to construct a test cell under saline ground water conditions for use as a soil mixed barrier wall to prevent the intrusion of salt water into fresh ground water aquifers and 2) a cutoff wall to prevent leakage of secondary treated sewage from a containment pond into surrounding ground water.

Cement-bentonite (c-b) self-hardening slurry walls are being constructed as a seismic retrofit to stabilize the downstream slope of Tuttle Creek Dam in Manhattan, Kansas. A full-scale test program was conducted to evaluate various slurry mixes along with two construction techniques capable of creating the required c-b transverse shear walls. The two methods tested were a crane-operated mechanical clam-shell excavator (CS) and a long-reach track-hoe (LR). The results of unconfined compression tests on hardened c-b samples constructed by CS and LR techniques were measured and the comparison revealed different unconfined compressive strengths (UCS). This paper presents UCS for both construction techniques and sample type, i.e., cored and wet-grab samples. The cause(s) of the differences in UCS and the impact on the remedial measures are discussed.

Comprehensive understanding of the long-term performance of cement-bentonite slurry trench cut-off walls is essential as these mixes may degrade when exposed to aggressive environments or when subjected to prolonged drying. A series of wetting-drying and immersion experiments was carried out to evaluate the durability characteristics of laboratory mixed samples and block field samples from 40 days to 11 years of age. For the wetting-drying tests, the samples buried in medium graded sand were subjected to periodical flooding and drying cycles. They were then used for permeability testing and unconfined compressive strength (UCS) testing. For the immersion tests, the samples confined in perforated molds were submerged in magnesium sulfate solution for 16 weeks and their microstructures were then analyzed using X-ray diffraction (XRD) technique. This paper identifies the effects of contaminant exposure on durability of cement-bentonite and the effects of aging by comparing 11 years old samples to younger samples. Test results showed that young or previously contaminated cement-bentonite mixes are more susceptible to sulfate attack than old or less contaminated mixes.

This paper presents the results of slump tests to evaluate the constructability of a model soil-bentonite (SB) slurry trench cutoff wall backfill comprised of a fine sand and dry sodium bentonite (4% of total solids mass), amended with different amounts of either powdered activated carbon (PAC) or granular activated carbon (GAC) (2, 5, and 10% of total solids mass). The activated carbon (AC) products are added to provide enhanced attenuation capacity of the backfill for miscible organic contaminants. The results indicate that backfill slump at a given water content decreases as the activated carbon content increases. This decrease in slump correlates with an increase in liquid limit of the backfill, suggesting that the activated carbon provides a degree of water adsorption capacity. Thus, a greater water content is necessary for the AC-amended backfills to exhibit a similar slump relative to the control backfill containing no carbon. However, the slump can be adjusted to meet typical field requirements with an appropriate addition of slurry or reduction in dry bentonite amendment, if such a reduction does not compromise the hydraulic conductivity of the backfill.

The conventional slurry trench method of construction to form low-permeability vertical barriers of soil-bentonite (SB), cement-bentonite (CB) and slag-CB have been widely used. More recently, in situ mixing methods to construct vertical barriers, such as deep mixing method (DMM) and the Trench Remixing and Deep wall method (TRD) have found increased usage. For the first TRD project in the United States, the method has been used for construction of test cells and is under consideration for the construction of a soil mixed barrier wall to prevent the intrusion of salt water into fresh ground water aquifers at the Alamitos Gap in southern California. To fully investigate the technology and its suitability for the application under consideration, laboratory and field studies (including construction and evaluation of two test cells) were conducted. This paper presents the results of various material formulations upon properties such as hydraulic conductivity and unconfined compressive strength. Laboratory studies demonstrated that mixtures of site soils containing saline pore water and blends of clay-water slurry, slag and Portland cement could be developed having measured values of hydraulic conductivity less than 1x10 -7 cm/s and being resistant to long-term degradation in the presence of the saline ground water.

Slurry cutoff walls have been used as vertical barriers to mitigate seepage of subsurface contaminant and to permit safe reuse of existing sites without extensive clean-up. The objective of the paper is to presents seepage analyses of soil bentonite (SB) cutoff walls that are part of the Dallas Floodway Extension project. The finite element program SEEP was utilized for the analyses. This flood control project in Dallas, Texas includes construction of wetlands for environmental mitigation purposes. The alignment of one of the wetland cells, Cell F, goes through the Linfield and UPRR landfills, requiring excavation of 1M yd 3 of landfill materials. Due to the presence of water in these landfills, migration leachate from the landfills into the wetland cell could occur over time. To mitigate migration of leachate into the wetland cell, two SB slurry cutoff walls are being constructed parallel to the longitudinal axis of Cell F. This paper presents the numerical modeling of the cutoff walls for three different wall configurations. The lowest factor of safety for the under seepage analyses of all three wall configurations was more than 1.2, required by the regulatory agency.

The East Side Access Project will connect the Long Island Railroad to a new terminal beneath Grand Central Station in Manhattan, NY. Contract CQ026 in Queens, NY involved construction of a bathtub work excavation, approximately 30.5 x 91 m in plan, excavated through the granular overburden to rock at depths between 18.3 and 24.4 m below working grade. Design of the excavation was complicated by several factors related to construction in an urban setting, notably that one area of the excavation would extend down and uncover an existing subway tunnel that would remain active during the work, excavation would proceed to 15 m below the groundwater table, and that plumes of contamination existed nearby that could not be disturbed by off-site drawdown. The primary means of support of excavation were a structural slurry wall extending to rock and connecting to an existing slurry wall (installed during construction of the active subway), and steel sheetpiles which had been installed over the existing subway. In order to ensure that the joints between the different means of excavation support did not allow water infiltration, zones of soil immediately outside of the joints were permeation grouted prior to the start of excavation to complete the watertight bathtub. Additionally, a groundwater cutoff bulkhead was required around all four sides of the existing active subway structure. Permeation grouting was used to close the gaps and joints and create the bulkhead around the existing structure to limit offsite drawdown and the movement of contamination. The permeation grouting was re-designed after bid time to allow all of the grouting to be performed from outside of the excavation. This reduced the risks associated with the performance of the grouting and allowed the contractor to accelerate his schedule. This paper discusses the design, re-design and execution of the permeation grouting program, including significant quality assurance and quality control measures.

The Lauenburg Lock is located next to a highway and a 40 m high slope with homes on top. Prior to the construction of a replacement lock, a monitoring system including 4 inclinometers, 8 extensometers and 11 groundwater monitoring points was installed. All data are processed and real time available in an online monitoring system. It was observed that there are natural deformations in the slope and changes in the groundwater head before the construction started. Both are dependent on meteorological conditions. During groundworks unexpected peaks in the groundwater monitoring points were observed. At the same time, the slope deformation did not produce any exceptional readings. An elevation of the groundwaterhead of up to 2 m was observed during trenching of the slurry wall. Over night it decreased to normal level and was found to be uncritical. Later one trench collapsed. Additional temporary groundwater monitoring points were installed close to the slurry wall. The readings showed peaks in the water head of up to 4.5 m, which were an explanation for the collapse. To enable further works to be carried out, vacuum drains were installed to temporarily lower the water head close to the actual works. The water pressure was effectively reduced and trenching could be carried out without any further problems.

Gravel pit reservoirs emerged in the mid-1980s as a solution to water storage in the Front Range of Colorado. The stratigraphy within gravel pits in the Front Range generally consists of sand and gravel deposits covered by thin clayey sand overburden. Beneath the sand and gravel exists claystone bedrock. When the aggregates are mined to the claystone floor, a storage bucket is formed by simply sealing the gravel highwalls. The earliest lined pits consisted of below grade earthen slope liners founded on bedrock and extending upward to the original ground surface. Soil-bentonite slurry walls constructed around the perimeter of a gravel mine property were introduced in 1990 as a lining system. Slurry wall liner systems allowed an owner to claim storage in both surface water and groundwater present in the void space of gravel deposits inside the slurry wall. Additional developments occurred when above-grade dams were constructed around gravel pits. This resulted in the increase in the size of a specified project from 1,000 to 2,000 acre-feet (1.2 to 2.4 million m 3 ) to 6,000+ acre-feet (7.4 million m 3 ). As the population of the Colorado Front Range grows, economic water storage is becoming a greater challenge. Increased competition for reservoirs has caused miners to coordinate with water storage purchasers at the conception of mine investigation work. This paper presents the development of gravel pit reservoirs through the presentation of multiple case histories. Many successful projects and a handful of failures caused by geologic conditions and improper construction techniques are discussed.

Based on the field test results, the consolidation mechanism of the negative excess pore pressure due to vacuum preloading is presented and analyzed in this paper. The variations in the physical and mechanical properties of soft soil under the mixed slurry wall (MSW) due to vacuum preloading are also analyzed via borehole samples. The test results show that the sealing effect of MSW composed of two-row piles is better than that of single-row piles. According to Darcy's law, the optimal width of the MSW was calculated. It is suggested that a MSW used as the outer boundary of consolidated zone should be constructed using two-row piles when the sand layer is thinner at the deeper positions. However, in order to reduce the hydraulic conductivity of MSW, cement should be added to the MSW when the sand layer is thicker. The dry density, wet density and shear strength increases, while the moisture content, void ratio and compressible coefficient decreases due to vacuum preloading. It was found that soft soil at a depth of 12.0 m under the MSW was also be consolidated.

The permeability of a containment wall is a topic of debate during design and construction. This paper presents the design phase laboratory test results for a quality control program developed to verify that a self hardening cementclay-slag slurry wall meets the performance criteria in the contract documents. The full QC program includes laboratory testing to evaluate the time-dependent changes of the slurry; bench-scale falling head piezometer tests to check the ability of the method to yield comparable results; a slurry wall test section to compare to the laboratory and bench scale tests; and finally the field implementation during wall construction.

Soil-bentonite (SB) slurry trench cutoff walls have been used for over 30 years as subsurface vertical barriers to control ground water flow and contaminant transport. Despite the millions of square feet of cutoff wall that have been constructed, little is known about the time-dependent behavior of the backfill and, in particular, the change in shear strength with aging. From experience, practitioners know that the backfill, which is initially placed as a semi-fluid material, gains strength with time. What has not been known is whether this time-related strength gain is due entirely to consolidation of the backfill or some other mechanism. This paper presents the results of laboratory and field testing of a SB slurry trench cutoff wall. Laboratory studies included consolidation and slump testing. Field studies included testing a constructed wall using vane shear, earth pressure cells, and settlement plates. The results of these tests demonstrate an increase in shear strength within a few days of backfill placement. This initial increase in shear strength is attributed to consolidation of the low-permeability backfill. The shear strength continues to increase with time, behavior that the authors attribute to two factors. The first is secondary consolidation or creep. The second is broadly termed “aging” and is attributed in part to the thixotropic nature of the bentonite used in the backfill mixture. Recommendations for the design shear strength for SB backfill are also included. Introduction The authors were presented with a unique opportunity to sample, test and instrument a SB slurry wall under construction in Delaware City, DE for containment of contaminated groundwater at an industrial site. The wall was approximately 1000-m long and typically 12to 19-meters deep. Field testing consisted of vane shear tests that were conducted at various time increments after construction and earth pressure cells that were installed in the trench at the time of backfill placement and monitored for some time afterwards. Samples of field-mixed backfill were taken for laboratory testing. Physical property testing Samples from the site were obtained as grab samples from field-mixed SB backfill (which includes a sandy base soil and bentonite) immediately prior to backfill placement in the trench. Based upon field requirements, the bentonite conent is estimated to be approximately 5%. The material was found to be a medium to fine silty clayey sand (SC) with an average of 23.7% fines with little variability from sample to sample as shown in Fig. 1 below. The average moisture content from 12 determinations was found to be 26.7%, typical of field-mixed and placed SB backfill. igure 1 Grain size distribution of Delaware City backfill (ASTM D422) he permeability of this material, based on extensive quality control testing of the fieldlump testing he time-dependent behavior of SB backfill was investigated in the laboratory using a 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 0.010 0.100 1.000 10.000 Grain Diameter (mm) Pe rc en t P as si ng (b y w ei gh t) Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Unified Soil Classification :SC

The 11th Avenue Railroad Underpass is located in Nampa, Idaho. The project involved replacing an old railroad bridge and narrow highway underpass beneath the main lines and switchyard of the Union Pacific Railroad with a wider, deeper structure. The new underpass extends to depths greater than p.1 meters (30 feet) below existing grade, and about 7 meters (24 feet) below the estimated high groundwater level. A major constraint was that railroad traffic could not be interrupted through the site during construction. This and other construction considerations largely drove the design and let the selection of structural slurry walls to provide both temporary and permanent excavation support and abutment walls. The new railroad bridge was preassembled in longitudinal halves on either side of the old bridge, and supported temporarily on structural slurry approach walls. Train traffic was shifted to one half of the old bridge. Construction of the structural slurry wall abutments for the opposite half of the new bridge and demolition of the corresponding vacant half of the old bridge were then undertaken simultaneously. When the abutment walls were ready, the adjacent half of the new bridge was jacked laterally into position and placed on the new abutment walls. Train traffic was moved to the completed half of the new bridge, and the process was then repeated to complete the new bridge. After the railroad bridge was completed, the new underpass was constructed, in effect, by tunneling under the new bridge between the abutment slurry walls. This included demolition and removal of the existing underpass.

The East Side Access tunnel Project in New York City will connect Long Island Railroad in Queens to Grand Central Terminal in Manhattan. The Queens segment of the project comprised of cut and cover and bored tunnels. The site in Queens primarily consists of glacial deposits with cobbles and boulders with high groundwater table. Construction of a proposed approach structure in Queens includes a combination of slurry walls and jet grout plugs for base stability and groundwater control of the excavation. The plugs are made of overlapping jet grout columns. This paper presents and discuses the results of a finite element analysis carried out to better understand the interaction between jet grout columns, glacial till and slurry walls and aid the design of jet grout plugs.

The slurry wall technique has undergone an evolution from its invention to its today’s status. In the early stages slurry walls were built with cable grab, later on with much stronger hydraulic grab and last but not least with the use of the cutter technique. The cutter allows thick walls with high verticality to extreme depths through hard soil and rock formations. With the rising demand of the construction of watertight diaphragm walls different joint systems have been developed. In addition to the rapid development of excavation systems it was necessary to improve slurry treatment and desanding plants, especially in conjunction with high performance trench cutters.

The Walter F. George dam was built in 1962 on the Chattahoochee River by the Corps of Engineers and it soon developed seepage problems. Two partial cut-offs were built in the past to attempt to remedy the situation, but the problems continued, jeopardizing the safety of the structure as well as reducing its power generating potential. In 2001 the Mobile district of the Corps advertised a design-build contract for the construction of a 200 feet deep cut-off in front of the concrete structure of the dam starting from 90 feet of water, cutting through a concrete lock structure, a submerged retaining wall and extending on both sides on the earthen embankments. The winning proposal of the joint venture of Treviicos and Rodio anticipated the use of a secant pile wall in the portion to be built in front of the structure, working from barges with a reverse circulation drilling rig, and a conventional slurry wall built with a hydromill rig for the portion out of the water.

Soil-Cement-Bentonite (SCB) slurry walls have been used with increasing frequency in recent years to provide barriers to the lateral flow of groundwater in situations where the strength of a normal soil-bentonite wall would be inadequate to carry foundation loads. The addition of cement to the backfill blend allows the backfill to set and form a more rigid system that can support greater overlying loads. Construction and quality control for the SCB wall is more demanding than that needed for conventional soil-bentonite slurry walls. Backfill mixing, sampling and testing of this type of wall involve more exacting procedures. Recommendations are made herein for methods to carry out pre-job design mix testing and in-field quality control testing for the most reliable results. Designing the SCB backfill is a complex issue involving conflicting actions of the various materials involved. While the SCB wall provides additional strength, permeability is one property that generally suffers in comparison to soil-bentonite slurry walls. A normal permeability specification would be a maximum of 1 x 10 –6 cm/sec. With special attention to materials and procedures, a specification of a maximum 5 x 10 –7 can be achieved. Data are presented from design mix studies and field-testing programs to illustrate the effect of increasing concentrations of the key materials in the mix design and also the impact of other factors such as time on the measured properties. Comparisons are made between soil-cement and SCB materials as used in slurry walls and other types of installations. The SCB material is normally highly variable, even when mixed under carefully controlled conditions; engineers must account for this variability in designs and when drafting specifications.