Contemporary Topics in Ground Modification, Problem Soils, and Geo-Support

In this study, the causes of distress (crack movement) in the face panels of a 244 m (800 ft) long and 4.6 m (15 ft) high retaining wall was investigated by instrumenting the active zone adjacent to the wall. The foundation of the retaining wall was placed in a CH soil few feet below the surface and the ground water table was about 7 feet below ground. Total of three boreholes were instrumented to determine the vertical and horizontal ground movements in the active zone and to determine the variation of matric soil suction adjacent to the wall. The instrumentation included tensiometers, extensometers and an inclinometer. Two additional boreholes were instrumented with extensometers and pore-water transducers to determine the consolidation settlement. The crack opening and closing in the retaining wall panels were measured regularly.

Anchor capacity is influenced by ground condition such as shear strength. In general, it has been known that the capacity in soft soil is several times lower that in rock. In addition, it also influenced by the configuration and size of the anchor zone as well. Four types of anchors have been introduced generally according to mechanism of stress transfer and how to be installed. Among them is a bell or under reamed anchor, which can increase resistance. However, the effect of enlargement of fixed zone is controversial. Since such an enlargement is formed by cut mechanically, there always exists so-called smear zone of ground which gives rise to the reduction of shear strength. This paper introduces PDT(Pulse Discharge Technology) anchoring method. The PDT anchoring method is to install an anchor using electrical power so called Pulse power. Since this technique can make not only a bore hole to be expanded but also the ground to be improved by compaction, the anchor installed by PDT is expected to develop shaft and end bearing capacity efficiently. In this study, as preliminary study, we introduce characteristics of ground expansion as well as improvement. In order for quantitative evaluation of the relation between pulse power and ground expansion a series of laboratory tests are conducted. The tests are carried out on sand with different relative densities and various number of pulse discharge. As a result, it is concluded that the expansion and soil improvement appeared to increase with an increase of the number of discharge and with a decrease of relative density.

Dyna Force sensor uses the elasto magnetic technology (EM) and non destructive testing (NDT) to direct measure stress level in prestressed strands or bars installed on ground anchors or post tensioning tendons. Dyna Force sensor can be used to rapidly read the change in load during proof and performance tests and compare with the pressure gauge and during the life on the anchor to monitor existing lock-off load. It can be used also to determine the load along the bonded length of the anchor allowing the contractor to increase or decrease this length. The paper presents Dyna Force operating principle and some applications. In conclusion, the elasto magnetic technology applied through Dyna Force is a new and easy to use approach to monitor anchor load during proof test and service life of the structure.

This paper contains analyses of an instrumented temporary soil nail wall in which strain-gauged nails were installed and monitored during and after construction. Three test sections were installed consisting of a total of 43 strain gauges on 10 soil nails and monitored for a total of nearly 6 months. The maximum stresses measured in the monitoring were significantly less than those predicted by the limit equilibrium design process used to analyze the walls. Loads continued to increase in the nails until the end of the monitoring program without any observable decrease in stress-accumulation rate. These observed mechanisms have far-reaching impacts on the design of temporary and permanent soil nail walls and should be further investigated with additional instrumentation.

The right downstream retaining wall of Hodenpyl Dam in Michigan had undergone significant lateral displacement due to global instability of the in situ soils. The remediation design called for installation of additional anchors bonded within a high plasticity, stiff clay layer. To increase the unit bond strength and reduce the potential for creep observed in other anchors installed at the dam, the contractor selected the Single Bore Multiple Anchor (SBMA) system with intensive, selective post grouting. The SBMA anchors have been lift-off tested four times since their installation. This paper describes the design and construction of the SBMA anchors, testing of a sacrificial SBMA anchor, lift-off testing procedures and results, and conclusions.

Combined with one shaft construction employing pneumatic caisson in Shanghai, in-situ measurement of ground deformation was conducted. Based on the particular construction process of pneumatic caisson, one kinematic numerical analysis method was proposed for evaluating its influence on the surrounding strata. Through comparisons between calculated results and measurements, the proposed mechanical model and numerical analysis method were verified.

More than 50 tiebacks were installed into a structural concrete slurry wall supporting a deep excavation. The tiebacks consisted of 7-wire strands and ranged in length from about 50–80 ft (15.2–24.4 m). Three of the tiebacks were fitted with load cells and were monitored for a period of 14 months. Results indicate that the tieback loads fluctuated over this period by as high as about 10 percent from the initial lock off load. The variation in load is attributed to large fluctuations in temperature, ranging from about 25–100 deg F (–4 to 38 deg C) over the monitoring period. A maximum load loss of about 1 kip (4.5 kN) for every 10 deg F (5.6 deg C) rise in temperature was recorded. This can be significant for excavations with restricted movement requirement.

Below grade foundation design and construction can be a complicated, multi phase process. Conventional means and methods have additional issues that at grade foundations do not. The cost factors and systems are dependent on soil conditions and vary by region, but the process remains fairly standard. Install temporary shoring, brace as excavation proceeds to final elevation, build your foundations, construct a permanent wall, waterproof, and work your way up out of the ground. These multiple contracting phases require form work, curing time, and possible offset from the property line. Subterranean structures offer shelter from the elements, minimal temperature variance, and maximize use of the property. Those benefits are overshadowed by the costly variables of building a geostructure. It is no surprise that underground construction can be more than twice the cost of above grade. For the past three years, domestic owners, consultants and contractors have begun to realize the benefits of below grade permanent sheet pile walls for parking and basement structures.

A new damage approximation method is proposed that directly relates ground distortions resulting from deep excavations to building damage. Several factors were considered for the method to accurately predict building damage in varying situations including; horizontal strains, critical strain criteria, wall dimensions, and wall flexibility. Previous methods of damage approximation have related ground distortions to varying degrees of general building damage by using simplified beam bending theory. A new damage approximation method is proposed that attempts to improve upon current methods relating ground distortions to specific building damage in terms of previously defined damage criteria. The proposed method quantifies building damages in terms of strain capacities and crack widths. The proposed damage approximation method was compared to measured crack gauge data and was shown to perform quite well.

The Bay Area Rapid Transit (BART) District will be extending BART service south along an 8.7-km (5.4-mile) -long corridor in the city of Fremont, California as part of the Warm Springs Extension (WSX). The WSX project will link the existing BART system to the proposed BART to San Jose extension. A segment of WSX is located in Fremont Central Park (referred to as the Fremont Central Park Subway Project). This segment is considered the most geologically and geomorphologically complicated portion of the project. The project consists of (1) an underground subway box being constructed not only in the middle of the largest park in Fremont and crossing under a lake, but also subject to high hydrostatic water pressure from the underlying aquifer and (2) a fill embankment over the Hayward Fault. This paper presents the geotechnical challenges that have to be addressed both in the design stage and during construction.

Two parallel retaining walls were constructed from 10.4 m embedded PZ22 sheet piles in order to indirectly measure the amount of earth pressure induced during excavation. Selected sheets were instrumented in an effort to measure bending moment and deflection, whereby the induced earth pressure could be discerned. Four sheets were instrumented, each with 16 strain gages (eight gages per flange) to detect bending moment. Steel tubing was attached to four additional piles for use with an inclinometer to measure horizontal movement. The soil between the walls was excavated in five equal lifts over a ten day period until the total depth of excavation was 6.1 meters. Strain gages were continuously monitored while inclinometer readings were taken at the completion of each excavation lift. The qualitative and quantitative results of the load tests showed no mobilization of lateral earth pressure on the walls with an excavation depth of 6.1 meters.

The Hydraulic Improvements at the Calumet Water Reclamation Plant project in Chicago, Illinois required excavation of over 76,000 cubic meters (100,000 cubic yards) of soil. To accommodate the excavation, an earth retention system (ERS) was designed and installed within the existing dense network of active utilities at the site. The potential for conflicts between the ERS and the utilities was very high. The use of three dimensional modeling, considerable pre-planning and design was required to ensure that a cost effective, stable and constructible earth retention system could be installed that met the project requirements yet did not disrupt the existing facility. This paper covers the development of the design, installation and performance of the earth retention system.

This paper will provide an overall description of the Block 76 project and discuss the approach for the selection of the earth retention systems employed on the site. In addition, the location and reasoning behind the use of underpinning and jet grouting will be discussed. A detailed account of the installation of the earth retention, underpinning and water cutoff systems will be provided. Soil conditions encountered at the site will also be discussed. Predicted versus actual earth retention wall movements will be presented. In closing a brief summary will be provided with regards to the 24" (600mm) diameter, 450tn capacity augercast piles currently in place for the new structure that is taking shape.

This paper presents the state-of-the-practice design and construction of a secant pile wall for a major real estate development in Lower Manhattan. At this site, the presence of a 1.5-meter wide rear alley between the adjacent buildings and the property line precluded the use of conventional underpinning. As an alternative, a secant pile wall was constructed to provide an excavation support system for the basement construction and to eliminate underpinning of adjacent buildings. The secant pile wall inherently created a dry excavation that avoided costly dewatering operations. The secant pile wall also served as the permanent foundation wall of the new building. The 58-meter long wall was completed in less than five months.

The Route 47 Improvements Project in Cumberland County, New Jersey involved widening Route 47 at the interchange with Route 55. The north and south bounds of Route 55 pass over Route 47 through two bridges supported on stub abutments. Three meter high soil nail walls were constructed in front of the abutments in order to accommodate the widening at the Route 55 bridge structures. The abutments of the Route 55 bridges are founded on shallow foundations and rest on top of a 1.0V:1.5H slope. Design of the soil nail walls was conducted using a limiting equilibrium approach. The finite element method was also used to estimate the deformations of the bridge abutments under the various stages of construction of the wall. Based on the finite element analysis, it was concluded that installing a system of tiebacks penetrating the abutment stem and tying it to a stable soil zone far from the back of the abutment would considerably reduce the amount of abutment deformation. The soil nail walls were instrumented to assess the stability of the system during and after construction. The instrumentation consisted of strain gages attached to selected soil nails for measuring the distribution of tension force along the nails and tiltmeters and optical survey points mounted at selected locations on the wall and abutment to detect any rotation and movement. The instrumentation data indicated that the system was stable and that the abutment and wall deformation were minimal and within acceptable limits. Design, construction and performance of the soil nail walls are discussed in this paper.

The Park Lafayette development currently under construction in Milwaukee, Wisconsin consists of two 20-story towers supported on a combination of spread footings and drilled shafts. The development includes four levels of underground parking, requiring a 14m (45 ft) deep excavation immediately adjacent to city streets and Milwaukee County property. The presence of the adjacent County property required an unprecedented level of pre-construction planning by the Developer, Construction Manager Hunzinger Construction Company, and Specialty Contractor Edward E. Gillen Company. The small site footprint required that the earth retention system be installed such that the retention system would also serve as the backside form for the foundation walls. The 13 corners in the foundation footprint complicated this necessity. Gillen and Hunzinger determined that soil nailing would be the most cost effective method to retain the excavation. To avoid conflicts with new foundation walls, the excavation footprint was oversized 150 mm (6 inches) on each side to allow for irregularities in the excavation and shotcrete face and lateral movement of the earth retention system. Construction of the soil nail wall proceeded through the winter of 2006 to 2007 with minimal delay. Optical survey monitoring by the construction manager indicated that the 150 mm (6-inch) wall offset was sufficient to allow foundation wall construction to proceed with modifications to neither the retention system nor the foundation walls.

Project documents and permits for construction of the Stemmers Run Relief Wastewater Force Main across the Back River in Baltimore County, Maryland specified a minimal width, sheet pile cofferdam and pile supported, work trestle approximately 518 m long. The contractor combined the impractically narrow cofferdam and trestle structures to minimize wetland disturbance and maximize access. The resulting structure was a braced, sheet pile cofferdam with timber deck mats as the work trestle for excavation, pipe installation, and backfill. Construction of this cofferdam/trestle progressed from the north shoreline, toward the south shoreline, to the two-thirds point of the structure. Then, working northward, the contractor excavated, installed the 1372 mm diameter pipe and support bents and backfilled the trench in increments of approximately 18.3 m. As the pipe installation progressed toward the north, the sheet piling and timber deck were removed. As sufficient materials were removed, the contractor began the process anew from the south shoreline using the reclaimed materials. Deep, very soft silts and organic clays and an unbalanced, hydrostatic head complicated the project. Concurrent pile driving, excavating, and backfilling in successive cofferdam sections required large backhoes and crawler cranes which controlled the design of the trestle and supporting sheet piles.

Sheet pile walls are one of the oldest earth retention systems utilized in civil engineering projects. The conventional methods used in the design of sheet pile walls are based on the limit equilibrium approach using active and passive earth pressures. These methods, based on force and moment equilibrium, do not consider wall deformations, which are important for serviceability considerations. For varying soil conditions and wall heights, effects of anchor location, sheet pile stiffness, anchor stiffness, and number of anchors on wall and soil deformations were studied. The free earth support method was used to calculate penetration depths of single-anchored walls for varying soil conditions and wall heights. Using these calculated penetration depths a parametric study was performed to investigate the effect of parameters considered on wall and soil deformations. Analyses were performed using the finite element method. The analysis results show that while having multiple anchor levels is the most efficient way to reduce wall and soil deformations, using pile profiles larger than the one required by the structural design can also be very effective. This paper presents the results and findings of the parametric study performed.

Conventional methods used in the design of anchored sheet pile walls are based on the limit equilibrium approach and they do not consider processes involved during construction. The sheet pile walls constructed on slopes may require both cut and fill operations. Varying amounts of cut and fill sections cause different loading and unloading of soils around the wall resulting in different wall behavior. The effects of simultaneous cut and fill operations for varying slope angles and cut to fill ratios on wall behavior were investigated using numerical methods. Sheet piling with a single anchor was considered. Wall deformations, bending moments, and anchor forces were investigated for the conditions studied. The results of the study show that the wall deformations and bending moments are significantly affected by the amount of cut and fill that occur during the construction of anchored sheet pile walls. This paper presents the results and findings of the parametric study performed for the sheet pile walls constructed on slopes, where both cut and fill operations are required during construction.

A multi-story office building in Seattle, Washington with four levels of underground parking was sited adjacent to the existing Alaska Way Viaduct in an area which had previously been occupied by turn of the century sawmills before being developed for commercial uses in more recent history. The soils at the site consist of approximately 8.5 m (29 ft) of sand and wood debris fill over estuary deposits and glacial soils. The ground water regime at the site consists of an upper and lower aquifer separated by an aquitard. The piezometric heads of the aquifers were 2.7 m (9 ft) and 2.4 m (8 ft), respectively, below existing grade. The proposed excavation was 13.1 m (43 ft) deep with a requirement that the shoring system extend an additional 7.6 m (15 ft) below the bottom of excavation to limit seepage from the upper aquifer into the excavation. Although initially tendered for construction with an owner designed secant wall or freeze wall system, the successful shoring contractor offered a design-build cutter soil mixed (CSM) shoring system which included pre-trenching the wall alignment under a cement-bentonite (C-B) slurry to remove the identified wood debris prior to installing the shoring system. This paper addresses the stability analysis and excavation of the C-B trench for removal of obstructions along with the design, construction, and performance of the CSM shoring system and associated depressurization of the deep aquifer.

This paper addresses the failure of a pile retaining wall constructed as a remedial measure to arrest instability of a highway embankment resulting from movement of its sideslope which was contiguous with the valley slope of a nearby creek. A drainage blanket was incorporated within the distressed section of the highway in 1983 to mitigate the pavement distress that was occurring. This remedial measure proved to be effective over a two-year period after which pavement distress re-occurred in the summer of 1990 following a period of increased rainfall. Further geotechnical investigation in 1990 resulted in the construction of a cantilever pile wall to isolate the highway from the perceived slide activity of the highway sideslope. Failure of this pile wall occurred in the summer of 1993 about 3 years after its construction, eventually requiring realignment of the highway. Failure to fully understand the site conditions from the inception of the geotechnical investigation played a major role in the short-lived performance of the remedial measures.

In this paper a deep excavation case history is studied to implement the findings of the numerical study. The 18-story Taipei National Enterprise Center (TNEC) building with five basement levels was constructed in 1991. The measured lateral deformations of inclinometers in the wall and 22-m further away from the wall are used to extract the constitutive model through the inverse analyses approach. The extracted constitutive model is used in predicting the other inclinometer measurements located at different distances from the wall and surface settlements behind the wall. The predicted behavior of the excavation and its agreement with measurements at the site are discussed in detail.

MSE/soil nail hybrid earth retaining walls provide a more economical design for applications in cut/fill situations than the traditionally used full height MSE and drilled shaft retaining walls. MSE/soil nail hybrid earth retaining walls use a soil nailed wall in the cut section and an MSE wall in the fill section. In spite of the significant cost savings they offer, hybrid walls have not seen widespread use primarily because of lack of understanding on wall design and performance. This paper describes an instrumentation and monitoring effort that was undertaken with the objective of improving our understanding of hybrid wall design and performance. In this project, two separate panels of a hybrid wall constructed in San Antonio, Texas were selected for instrumentation and monitoring. The first wall panel consisted of a 4.0m soil nail wall and a 5.4m MSE wall while the second wall panel consisted of 5.0m soil nail wall and a 4.4m MSE Wall. The instrumentation scheme for the wall included vibrating wire strain gages, vertical inclinometers, horizontal inclinometers, and tiltmeters. The data collected from these two instrumented wall sections provide valuable insight to the mechanisms controlling the performance of MSE/Soil Nail Hybrid Wall systems.

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.

Cement grout encasement is the most common means of providing corrosion protection for strand anchorages for earth retention applications in the United States. The grout surrounds the strand and wedges and completely fills the wedge pockets. The effect of the grout on the performance of the anchorage is unknown and the ability to develop significant additional capacity above the lock-off load has not been verified by testing. A series of tests were conducted to determine if neat cement grouted strand anchorages can reliably develop load carrying capacity above the load at which they are locked off. The tests considered a range of lock-off loads, grout strengths, and surface condition of the wedges (clean or rusty). Baseline testing of ungrouted anchorages was also performed. Test results indicated that grout with compressive strength less than 38 MPa (5500 psi) did not adversely affect the ability of anchorages to develop load carrying capacity above the lock-off load, while very high strength grout with compressive strength greater than 81 MPa (12,000 psi) adversely affected performance. Rusty anchorages also performed poorly.

In very soft soils, the use of stone columns can be problematic due to the lack of adequate lateral confining pressure. In these situations, to provide the required lateral confining pressure and to increase their bearing capacity, stone columns can be encased by a suitable geosynthetic. Using a high-strength geosynthetic for confinement not only increases the strength of a stone column, but also prevents lateral squeezing of the column due to movement in the very soft surrounding soil. This paper describes 3D finite element analyses carried out to simulate the behavior of a single geosynthetic-encased stone column in a soft clay soil using the computer program ABAQUS. The influence of geosynthetic stiffness, column diameter, and the stiffness and friction angle of the column material were studied in the numerical analyses.

This paper presents a new method to improve embankment on deep soft clay in China. The method, briefly named D-M method, combines the prefabricated vertical drains (PVD) and the cement deep mixing method (DMM) together to consolidate deep soft soil foundation. The short deep mixing columns improve the shallow soft soil and long PVDs accelerate the dissipation of excess pore pressure in the deeper soft soil layers. To evaluate the efficiency of the D-M method, a numerical study was conducted using the design parameters obtained from the Huaian-Yancheng Highway project by the 2-dimensional finite element software Plaxis. Results showed that the new method succeeds in consolidating deep soft soils below the deep mixing columns and improving the stability of the highway embankment.

Stone or sand columns in soft clays have been used to increase the load carrying capacity, reduce the settlement, and decrease the generation of excess pore water pressure during loading. The main objective of this paper is to investigate the effect of sand columns on the undrained shear strength of soft clayey material. For this purpose, consolidated undrained triaxial tests were performed on normally consolidated Kaolin specimens that were reinforced with sand columns and tested at confining pressures of 100, 150, and 200 kPa. The parameters that were varied are the diameter of the sand columns, the height of the column, and the confining pressure. Results indicate substantial improvements in undrained shear strength reaching 75% for a maximum area ratio (ratio of area of sand column to area of specimen) of 17.8%. The data collected supports the hypothesis of a "critical column length" that is greater than about six column diameters, beyond which the increase in undrained shear strength due to the presence of the sand columns becomes negligible. Finally, the data did not show any clear indication of the effect of the confining pressure on the improvement in the undrained shear strength of the "reinforced" clay specimen.

This paper presents instrumentation results and analyses of a low-height, geosynthetic-reinforced, column-supported embankment constructed in Brazil. The approach involves back analyzing relevant properties of the embankment fill and geogrid reinforcement and applying the Load Displacement Compatibility (LDC) approach to calculate geogrid deflections in a unit cell of a square pile cap array. The results show that the LDC approach is consistent with the observed response of the embankment.

This paper describes the investigation and back-analysis of a full scale jet grouting field trial using the triple fluid technique, to study the performance of jet grout column formation in soft marine clays. Cored samples obtained from the grouted soil mass indicated that although jetting in the marine clay was satisfactory, the lower levels encountered stiff desiccated clay, resulting in a smaller column size being formed. The cutting performance was evaluated using an analytical model for jetting with a compressed air shroud. The additional jet penetration distance achievable in using a compressed air shroud was estimated to be approximately 160%. The importance of obtaining accurate soil strength profiles for the soils to be grouted, including stress history, is emphasized.

Grouting has been successfully used for decades as a ground improvement technique to stabilize and retrofit historic structures. Over the years, new technology, equipment, and chemicals have improved the feasibility of grouting over a wide range of applications. However, near real-time, in situ control methods to assess the effectiveness of ground improvement following subsurface grouting are lacking. Currently, the most commonly used quality assurance method is to obtain Standard or Cone Penetration Test (SET or CPT) measurements before and after ground treatment at pre-defined locations, typically between column/impact/injection locations to observe changes in relative density of in-place materials. All these methods are based on point measurements at specific locations and do not represent the overall treated ground mass. A volumetric, non-destructive, surface seismic evaluation method, that uses a state-of-the-art algorithm, was recently developed to collect and analyze seismic data describing the subsurface conditions. This relatively rapid and inexpensive seismic method was utilized in Rocky Mountain National Park, Colorado, during rehabilitation of a historic placed-rock armored slope structure located below roadway grade along the outboard lane. Compaction grouting was selected to stabilize roadway settlement caused by piping of a failed culvert within the fill while preserving the historic and aesthetic character of the structure. The seismic method proved effective in producing accurate pre- and post-grouting volumetric difference images that depicts the effect of grouting, including the resultant grout columns and ground densification characteristics.

This paper describes an unusually deep grouting program that was undertaken to arrest the unexpected settlement that occurred during construction of an Amtrak bridge over the Thames River in Connecticut. During construction, a caisson started to settle and tilt when new, adjacent piles were installed. A remedial grouting program was performed to arrest the settlement. The target grout zone was the permeable and erratically-dense sand and gravel stratum beneath the caisson, at a depth of about 40 to 52 m (130 to 170 ft) below the river surface. Grout holes were placed around the perimeter of the caissons as well as through each caisson. A computerized data acquisition system was used to provide real time monitoring of grout injection parameters and rapid evaluation of the effectiveness of grouting as work progressed. Over one million gallons of microfine cement grout were pumped during the course of 11 months work. Cores of the grouted soils were obtained to confirm grout coverage and properties of the grouted soil. Eventually, the grout stabilized the pier and halted the creep movement. This paper describes the grouting program, grout mixtures, effects of various admixtures, and quality control measures.

Jet-grouting is usually used in underground construction in the Shanghai soft deposits. In some cases, jet-grouting is conducted horizontally. However, immediately after the mixing, the soil-cement admixture is in a fluid state, which will flow out from the hole. In order to solve this problem, Twin-Jet Technology was invented to solidify soft soil instantly. Two types of binders with cement and accelerator such as sodium silicate are jetted under high pressure of about 10 to 40 MPa and mixed with in-situ soil to create the instant solidification. A field test was conducted in the soft clayey deposit in Shanghai. Field and laboratory results showed that the admixture can be gelled within 10 to 20 seconds. The diameter of the jet-grouted column reached 1.2 m and the strength after 14 days reached 1.2 MPa.

Lateral load tests were performed on a full-scale pile cap in clay before and after construction of eight 1.5 m diameter jet grout columns to a depth of 3 m around the pile group. Jet grouting with a cement content of about 400 kg/m³ (20% by weight) increased the average compressive strength of a soft, plastic clay from 40 to 60 kPa to an average of 4500 kPa. The lateral resistance was increased by 2200 kN or 177% and the initial stiffness was increased by 400%. About 65% of the increased resistance could be accounted for by passive pressure and side/base shear on the jet grout mass; however, the remaining 35% increase must be due to the interaction between the piles and the strengthened soil. Jet grouting provides a method to significantly increase the lateral resistance of pile group foundations at costs much lower than typical structural approaches.

This paper describes the application of cold-weather concreting technology to soil stabilization with cement. For concrete, the typical approach involves the use of chemical additives to depress the freezing point, accelerate the curing process and initiate other changes that allow cementitious reactions to proceed at low temperatures. Likewise, cementitious reactions are also critical to the performance of cement soil stabilization. To that end, a set of experiments was conducted to evaluate the influence of three commercially-available chemical additives on the unconfined compressive strength of a local soil stabilized with 6% cement by weight. In particular, the chemical additives were tested at three dosage levels, with strength measurements taken at 1, 7 and 28 day curing periods, and two different curing temperatures. The control (unmodified) mixture resulted in an average 7-day strength of 295 kPa (42.8 psi) when cured at –2°C (28.4 °F). For the same mixture at the same curing temperature, the average 7-day strength increased to 1318 kPa (191 psi), 1050 kPa (152 psi) and 1332 kPa (193 psi) for the Gilco, Polarset and Daraccel brand chemical additives, respectively. As tested, the incremental cost associated with using these additives varied from 8–41%, making them a viable alternative to extensive undercutting and/or geosynthetics.

China generates up to 4 million ton dried sewage sludge every year. How to reasonably handle this huge amount of hazardous waste has become a concern. However, sewage sludge is hard to handle due to its poor geotechnical properties, such as high water content, low compressibility, and low resistance to environmental change. The use of solidification/stabilization (S/S) into sewage sludge can improve not only its geotechnical properties but also its environmental properties (e.g. stabilization of the pollutants in the sludge). Therefore, S/S can make the waste re-usable as a construction material or pre-treat it prior to landfill disposal. In this study, ordinary Portland cement (OPC) and calcium-bentonite were used as the S/S for local sewage sludge from the Nanjing Wastewater Treatment Plant in China. Geotechnical properties of the solidified sludge were studied in terms of unconfined compressive strength (UCS) and durability after the wet and dry cycles. The test results show that in a short curing time, cement alone-S/S sludge had a low compressive strength but a significant improvement was observed when bentonite was added to replace some amount of cement. In a long curing period, cement played a major role in increasing the compressive strength as compared to bentonite. In addition, initial water content of sewage sludge influenced the UCS, which should be taken into account before S/S. The test results of the dry and wet cycles indicate that bentonite was beneficial to improve the durability of solidified sludge when the ratio of bentonite was less than that of cement. Considering both UCS (>100kPa) and dry/wet cycle (<30% relative mass loss) requirements, the ratios of sewage sludge, bentonite, and cement should be approximately 5:1:2.

The soil type can affect significantly the effect of cement stabilisation. In order to investigate this, five types of soils were mixed with cement at various cement proportions in order to evaluate the large variation of compressive strength values. The compressive strength of the cement treated soils was determined for a curing period of the cement equal to 7 and 28 days. It was obvious that the soil type is a controlling factor on the rate of increase of compressive strength with increasing cement content. Other factors affecting strength are the curing time of cement and the optimum water content.

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.

In the design of a foundation, the settlement of the foundation may exceed allowable design criteria even with a competent bearing stratum. In such a case, a pile foundation system may be adopted using piles as a settlement reducing component. In this paper, Disconnected Pile Foundation (DPF) system, which installs disconnected piles underneath the footing and uses the piles as ground reinforcements, is studied as a cost effective design method against the classical pile foundation system. To this end, large size loading tests were carried out on weathered ground, changing area replacement ratio and length of piles. The results indicated that the settlement of the reinforced ground was reduced by 46–85% from that of the unreinforced original ground. The correlating formula between the area replacement ratio and the load bearing ratio of piles was derived from the test results and numerical analysis. From the correlation, a design method determining the size and the quantity of the disconnected piles to enhance the bearing capacity of original ground to the desired value was proposed based on settlement criteria.

With increasing levels of seismic awareness and design-level earthquake accelerations, Geotechnical Engineers are challenged to find cost effective solutions to address both static and seismically induced settlement in high seismic areas. In Salinas, California a relatively heavy, one and two-story structure was recently constructed in an area of relatively deep, intermittent, layers of liquefiable soil resulting in the potential for excessive total and differential settlements. A traditional foundation system of driven piles with structural slab similar to the new surrounding buildings was initially considered. Although this option addressed static settlement control and the potential for excessive seismically induced differential settlements, the solution was not considered economically viable and posed a risk to adjacent historic, unreinforced masonry structures. Alternatively, an innovative soil reinforcement method consisting of a stiffened geo-grid reinforced engineered fill over reinforced soil utilizing an evenly spaced Rammed Aggregate Pier system was used to support the building. The reinforced soil mat was designed to control static settlement from the building loads and reduce seismically induced differential settlements to within allowable project tolerances.

Dry Jet Mixed (DJM) columns and Prefabricated Vertical Drains (PVDs) have been combined to improve soft ground for the Huai-yan Highway in China. This method could make the mixing of DJM columns easier and more homogeneous since the drainage of water through pre-installed PVDs reduces the excess pore pressure induced by the installation of DJM columns. In addition, the strength of the improved ground can be further quickly increased when the embankment load is applied at the existence of the PVDs. A two-dimensional plane-strain numerical model was adopted to analyze the consolidation of the DJM-PVD improved ground under the embankment load. The DJM columns and the PVDs in the treated ground were simply converted to DJM walls and PVD walls to obtain an equivalent plane-strain model. For comparison purposes, the conventional PVD improved ground, the DJM improved ground, and the unimproved ground were also analyzed. The numerical results showed that the DJM-PVD improved ground consolidated the fastest among these four types of ground. The stress concentration on the columns allows excess pore-water pressure in the surrounding clay to dissipate more quickly than that in the PVD improved ground.

The Piedmont Triad International Airport (PTIA), Greensboro, NC is undergoing an expansion as a result of the construction of a regional hub for Federal Express. Part of the construction includes an embankment over an alluvial floodplain in a wetlands area. A hybrid ground modification technique was used to stabilize the soft ground, consisting of geogrids, wick drains and rock toe berms. An instrumentation program was implemented to evaluate the changing properties of the alluvial soils, lateral displacements of the embankment foundation soils, settlement of the embankment, determine the fill placement rates or appropriate waiting periods, and to prevent slope failures from occurring. This paper highlights key features of the design and instrumentation system. It describes the project conditions and considerations, the instrumentation system that was installed, the results obtained during construction, and practical issues that were addressed during construction.

As part of the upgrade plans for the U.S. Highway 90 and Highway 6 Interchange, the Texas Department of Transportation (TXDOT) proposed the construction of a series of bridges and ramps. The bridge abutments and access ramps required the construction of Mechanically Stabilized Earth (MSE) retaining walls with heights of up to 8.2-m (27-feet). The weak clay foundation soils along the wall alignment presented global instability, settlement, and bearing capacity challenges. As an alternative to massive over-excavation and replacement or preloading with a surcharging, the design team and the Texas Department of Transportation selected a Rammed Aggregate Pier solution. The Rammed Aggregate Pier system (RAPs) increases the factors of safety for bearing capacity and global stability as a result of the high angle of internal friction achieved during ramming and reduces the magnitude and time of settlement by increasing the overall stiffness of the foundation soils and providing a drainage pathway for dissipation of excess pore water pressure. The performance of the Rammed Aggregate Pier-supported walls was monitored using a suite of geotechnical instrumentation consisting of vertical and horizontal inclinometers, vibrating wire piezometers, and Sondex vertical settlement gauges located near the critical sections. The instrumentation was monitored for approximately one year and indicated acceptable performance. This paper discusses the results of the monitoring program of an MSE wall supported by the Rammed Aggregate Pier system. This work is of particular significance because it is the first MSE wall support application performed in Texas and the first instrumented wall project supported on Rammed Aggregate Piers funded by the Federal Highway Administration (FHWA).

The creep of geosynthetics leads to the decrease of long-term strength and the increase of deformation. More importantly, the influences of creep of geosynthetics are also affected by the creep properties of soils. In this paper, the effects of creep of geosynthetic-reinforcements are investigated using Finite Element procedure, on the context of its relations to the creep of backfill soils. The nonlinearity and creep of both geosynthetics and backfills were considered in the procedure. A model MSE walls at a height of eight-meter was analyzed using the Finite Element program ABAQUS. Geosynthetic reinforcements with different rates of creep were analyzed to investigate the effects of relative creep on the responses of the model MSE wall. It is found from the analysis that the relative creep rate between geosynthetic reinforcement and backfill soil is very important to the responses of the model wall. Both the reinforcement loads and the stress states in the soils were influenced by the relative creep rates of the two materials.

Construction, instrumentation, and lateral load testing of eight 0.9m (36in.) diameter columns solely supported by the geogrid-reinforced backfill behind a 6m (20 ft) tall MSE wall was conducted for the Kansas Department of Transportation (KDOT). This paper describes the instrumentation of the wall and the performance of that instrumentation. Instrumentation included 24 pressure cells, 16 inclinometer locations, 112 strain gauges, 20 telltales, 84 photo target locations on the wall facing, and load cells and LVDTs associated with lateral load and response. A detailed discussion of the photogrammetric process used to remotely measure wall deflections through the use of cameras and AutoCAD is presented. A discussion of the relative benefits of the different methods of instrumentation is included.

A major geotechnical slope failure occurred at Sta. 1663 on the US 70 Design-Build project in New Mexico a year after construction. The 1663 reinforced soil slope was 7.6 m (25 ft.) high and constructed at 0.5H:1V. A slope stability-type failure occurred, with movement associated only with severe rain storms. This case history study will describe the project site conditions, design methods, failure monitoring and analysis, and reconstruction of the RSS. The authors were involved in all aspects of design, construction, forensic evaluations, reconstruction, and claims resolution. The failure is notable because following reconstruction, the contractor was successful in a dispute claim based upon differing site conditions. This paper describes the range of project evolution from design, failure monitoring, forensic evalutions, and reconstruction, to the dispute resolution process and findings.

The Cherry Island Landfill (CIL), located in Wilmington, DE, is undergoing a major expansion to increase its service capacity. To increase landfill volume, a mechanically stabilized earth (MSE) wall is being constructed along three sides of the site. Very soft, compressible soils characterize the subsurface conditions, creating the potential for large settlements and widespread slope stability issues. To facilitate strength gain of the foundation soils, the proposed design includes prefabricated, vertical drains (PVDs) and staged construction of the MSE wall. To reduce lateral spreading movements and improve the system's global slope stability, high-strength geotextile has been placed beneath the MSE wall. As a component of the project's instrumentation program, the geotextiles have been instrumented with strain gages to monitor the performance of the reinforcement. This paper discusses the methodology used to install and monitor the strain gages and presents lessons learned from gage performance to date.

Pavement damage is heavily influenced by seasonal variations in the environmental regime and by externally applied loads. The state of the art methodology currently evaluated by pavement engineers focuses upon coupling the effects on pavement performance of moisture content/matric suction properties of unbound materials with the external stresses. The literature review showed that several equations have been proposed to incorporate moisture variation effects on resilient modulus; however, the limited models available lack fundamental principles or have not been properly validated. A feasibility study on cohesionless granular base material is presented, whereas matric suction was controlled during drained and measured during undrained resilient modulus tests. It is apparent that certain modifications in the recommended stress state conditions of the NCHRP 1-28A protocol may be necessary when measuring matric suction due to the axis-translation needed during the test. Difficulties associated with the test include the current confinement fluid, which allows for air diffusion during the suction equilibration stage. Preliminary results show that the k₁-k₂-k₃ parameters used in the approved AASHTO Mechanistic Empirical Pavement Design Guide (ME-PDG) may be functions of the suction applied to the specimen during the test protocol.

This paper describes a case study where subgrade soils were stabilized with Class C fly ash to create a working platform during reconstruction of a 1.2-km section of rigid pavement in US 12 between Cambridge and Fort Atkinson, Wisconsin. The subgrade soils were blended with cementitious fly ash to increase its bearing resistance and stiffness. Resilient modulus (M_r), unconfined compression strength (q_u), soil stiffness gauge and dynamic cone penetrometer tests were conducted on the subgrade alone and fly-ash stabilized subgrade (FASS). Falling weight deflectometer (FWD) tests were conducted on the as-built pavement. After 14 d of curing, M_r of the field-mixed FASS ranged between 60 and 129 MPa and M_r of the laboratory-mixed FASS ranged between 115 and 167 MPa, whereas the M_r of subgrade was between 34 and 42 MPa. q_u of the laboratory-mixed FASS was four to nine times the q_u of the subgrade, while q_u of the field-mixed FASS was up to three times q_u of the subgrade. In situ stiffness and dynamic penetration index also illustrated that the addition of the fly ash and compaction increased the strength and stiffness appreciably. Moduli back-calculated from FWD tests showed that the modulus of the FASS varies seasonally.

Adding chemical agent to stabilize problematic highway subgrade soil is a common engineering practice in the United States. Due to the fact that theoretical accomplishments in soil chemical stabilization lag far behind the engineering practice, laboratory testing, which is expensive and time-consuming, is almost always necessary to determine the effectiveness of the soil stabilizer in enhancing engineering properties of the soil. Over the years, large amount of valuable data from laboratory tests on stabilizing different soils with different chemical stabilizers was accumulated in the literature. Efforts to extract the relationships and associations from the existing test data in order to provide guidance for new soil chemical stabilization cases were carried out for many years, however, due to the technology (statistic regression) limitations, reliable models are still not available. In this paper, Neuronet (NN) approach to study soil chemical stabilization was introduced. NN model to predict the unconfmed compression strength (UCS) of the stabilized soil was built based on the experimental data from stabilizing three representative Kansas embankment soils with five chemical stabilizers. The results showed that the trained NN model could precisely predict the UCS of stabilized soil. Furthermore, NN model enables us to study the significance of each input factor, thus providing a powerful tool for optimizing the mixture and construction design.

Data from 96 resilient modulus laboratory tests on four base materials and four subgrade soils was used to develop a predictive model capable of estimating changes in resilient modulus as a function of changes in the state of stress, moisture and density. Test specimens were compacted at optimum moisture/density conditions and then dried or soaked to various moisture conditions. Both standard and modified compactive efforts were used. Plastic, subgrade-type soils were especially affected by moisture. Non-plastic, base-type materials were more sensitive to changes in the state of stress.

Geosynthetics have been used for base reinforcement since 1970s. Numerous research has already been carried out for planar geosynthetic reinforcement but limited research has been conducted for three-dimensional geocell reinforcement. Literature review has also demonstrated a significant gap between the applications and theories of geocell reinforcement outlining the need for more research. This study was to investigate the behavior of reinforced bases using a single geocell under static and repeated loads on a loading plate. The experimental results show that the single geocell could increase the stiffness by approximately 50% and the maximum load by 100% as compared with those of the unreinforced base. The repeated test shows that the geocell-reinforced base had the percentage of elastic deformation increase with the number of cycles of the repeated load up to 95%.

Saving of resources is a significant indicator to evaluate social and economic benefits of a highway project. The purposes of this study are to investigate the feasibility of using recycled building materials as base, subbase, and subgrade and provide guidelines for selection and performance evaluation of recycled materials in future projects. This study first considered the requirements for building waste materials which could be recycled. Laboratory tests were conducted to evaluate whether the waste materials fulfilled these requirements. Cement and High strength water stable Earth Consolidator (HEC) were employed as stabilizing/recycling agents. Orthogonal analysis was adopted to evaluate the effect of gradation, type, and quantity of stabilizing/recycling agents on unconfined compressive strength (UCS) and resilient modulus of recycled materials. The laboratory study shows that the use of the recycled waste materials as highway base, subbase, and subgrade is feasible and would fulfill its requirements.

A controlled field study was conducted to evaluate the influence of underlying layer support conditions on roller-integrated machine drive power (MDP) measurements. Multiple layers of granular base material were placed over a section of wet/soft subgrade and a section of concrete base for comparison. The material was compacted in layers using a 12-ton vibratory padfoot roller. MDP and in-situ spot test measurements were obtained on each layer and the results were statistically analyzed. Results indicate that compaction layer MDP measurements are strongly dependent on stiffness and heterogeneity of the supporting layer. If relatively stable and homogenous support conditions exist, the effect is not statistically detectable. Although the compaction layer properties (as measured by in-situ test measurements) are relatively uniform, the MDP measurements tend to capture the variability of the underlying layers. Post-construction tests by carefully excavating the compaction layers showed significant improvement in stiffness of the granular base layers compared to the initial compaction layer measurements. The reason is attributed to possible densification of underlying layers during compaction of the layers above and an increase in lateral stresses during compaction.

The use of Reclaimed Asphalt Pavement (RAP) aggregates in road construction reduces both the amount of construction debris disposed of in landfills and the rate of natural resource depletion. This paper presents the results obtained from a series of repeated load triaxial tests conducted on both untreated and treated RAP aggregates. Test specimens were compacted at density corresponding to optimum moisture content with different dosages of ordinary Portland cement (Type I/IT) with fibrillated polypropylene fibers. The resilient moduli of untreated aggregates varied between 180 and 340 MPa and that of cement-fiber treated aggregates varied between 200 and 580 MPa. Effects of cement and fiber dosages on the moduli enhancements of RAP aggregates are explained. Structural coefficients of these materials are also presented.

Low volume conventional pavement test sections with different base course thicknesses were recently constructed at the University of Illinois over a weak subgrade to evaluate pavement response and performance from accelerated loading. This paper presents the full-scale test study measured pavement responses used to validate the stress- and direction- (anisotropic) dependent unbound aggregate base behavior. Field validations involved comparing measured full-scale pavement test section responses with the predicted ones using both the isotropic and anisotropic aggregate base modulus characterizations. The nonlinear cross-anisotropic base characterization was needed to accurately predict several of the full-scale pavement section field responses and observations, such as the vertical deformation on top of subgrade, hot mix asphalt fatigue strains, and especially the large horizontal base course aggregate movements measured in the direction of traffic loading. The findings of this paper support the development of next generation of highway as well as airport pavement infrastructure by employing advanced technology and the detailed knowledge on the nonlinear, anisotropic aggregate base behavior gathered in the past 15 years of research activities.

Elastic theory is used to back-calculate the drained secant soil modulus from loads and settlements measured in full-scale load tests on footings in axial compression. The moduli are evaluated at L₁ (the end of the initial linear region) and at a settlement of 1% of the foundation width. These drained soil moduli are normalized by standard penetration test results at each site, and the normalized values are correlated effectively with the soil stress history, stress state, and stress level. The resulting correlations will be useful for footing design.

This paper presents a microscale approach to analyze the seismic response of a spread footing system founded on a liquefiable granular soil deposit. The approach utilizes a three-dimensional transient fully-coupled hydromechanical model while taking into account the effects of soil-foundation interaction. The porous soil medium is modeled as a mixture of two interpenetrating phases, namely the fluid phase (water) and the particulate solid phase. The fluid is idealized as a continuum by using averaged Navier-Stokes equations that account for the presence of the solid particles. The Discrete Element Method (DEM) is employed to model the assemblage of these particles. The interphase momentum transfer is modeled using an established relationship that accounts for the dynamic change in porosity. The spread footing is idealized as a rigid block and its motion is described by the resultant forces and moments acting upon it. A computational simulation is conducted to investigate the response of spread-footings on a saturated granular deposit when subjected to a dynamic excitation. Results of the conducted simulation showed that the foundation sustained excessive settlement as the ground shaking progressed. The conducted simulation appears to capture essential dynamic response patterns typically observed in such systems.

Presence of firm soil near the ground surface favors the construction of a shallow foundation. The shallow foundation is also an attractive option when combined with ground improvement techniques (such as geosynthetic reinforcement) even in weaker soil. This study presents the bearing capacity estimation of a shallow foundation on a granular soil underlain by a rigid base using the Discrete Element Method (DEM), which is suitable for granular media. A physical model test of the shallow foundation on sand was conducted using a plate load test in the laboratory. The DEM model of the plate load test simulated the load-settlement behavior of the shallow foundation. The failure model of the foundation under this condition was investigated.

Detailed foundation analyses showed the feasibility of supporting the abutments of a two-span bridge on spread footings founded on overconsolidated glacial till. Embankments were used to preload both abutment areas prior to footing construction to reduce long-term settlements to tolerable amounts. The design-build team worked with the Minnesota Department of Transportation to develop a cooperative instrumentation program to monitor bridge performance during construction and provide data for comparison with the anticipated foundation response during the staged construction process. Instrumentation included optical survey targets, inclinometers, earth pressure cells, and tiltmeters. Monitoring data indicated overall good agreement between predicted abutment behavior and the measured response.

Bearing capacity of rectangular footings was simulated with three-dimensional finite difference program. In the analysis, soil is modeled using Mohr-Coulomb model. Shape effects on bearing capacity of rectangular footing are evaluated without using the conventional superposition. To avoid error induced by superposition, cohesion and soil unit weight are normalized as one parameter. Numerical results show that bearing capacity of rectangular footing decreased with the increase of footing aspect ratio. The effects of footing shape are also different with the characteristics of soil. In general, effects of footing shape are more obvious for soils with high cohesion, while they are slight on soils with low cohesion.

Shallow foundations are more economical than deep foundations and are utilized to support many different types of structures in our society. However, one type of structure to which shallow foundations have not seen widespread applications in Ohio and elsewhere is highway bridges. This may be because most bridge engineers question shallow foundation's ability to maintain adequate load-carrying capacity in all environments. The research team at Ohio University continued its study of shallow foundations at highway bridge construction sites in Ohio. At one of these sites, A-2-4 and A-3a soil types were encountered in a borehole. The central pier footing was instrumented with sensors and monitored during construction. The field instrumentations consisted of multiple sensors and stations for recording contact soil pressure under the footing, settlement of the footing, and tilting of pier columns tied to the footing. A USGS quality bench mark was incorporated to establish a solid permanent bench mark at the site. The field performance data collected in the study provided further insights into how contact soil pressure, footing settlement, and columns/wall tilting were correlated with each other throughout various construction stages. The study also produced outcome on general reliability of a settlement prediction methods outlined in the AASHTO LRFD Design Specifications.

A large coal fired operating plant in the Ohio River Valley had a need to develop a disposal facility for residual waste from its newly installed Flue Gas Desulfurization (FGD) system. Siting studies were conducted resulting in the selection of a site located partially over an inactive fly ash reservoir (FAR 1) which was undergoing closure and partially over a remnant mine spoil disposal site. While the selected site would allow for environmental and operational advantages, significant engineering design and construction challenges had to be addressed. This paper provides information on the challenges that relate to the design and permitting of this residual waste landfill. Specific issues addressed include: (1) boundary issues (i.e., existing mining highwall, valley stream, and 45-m high dam); (2) potential for differential settlements of the foundation subsoils and effects on leachate collection and piping systems; (3) design of a subsurface drainage system to collect and transmit consolidation waters; and (4) impacts to landfill drainage systems resulting from liquefaction of the underlying fly ash during the design seismic event.

In a Piezocone Penetration Test (PCPT or CPTu), the probe can be stopped at a desired depth during penetration, and the excess pore pressure generated around the cone can be measured as dissipating u_t versus time, t. Using the rate of dissipation, it is possible to estimate the value of the soil deposit's coefficient of consolidation and thereby determine changes in hydraulic conductivity. Theoretically the dissipation is complete as u_t approaches in-situ equilibrium pore pressure, u₀. In fine-grained soils time required for complete dissipation or even 50% dissipation maybe very long, making the test impractical. The in-situ (equilibrium) pore pressure, u₀, can be estimated from a partial dissipation record requiring a shorter dissipation, by extrapolating the measured u_t data on an inverse time scale (i.e. u_t against l/t). Based on this partial dissipation test, the stress history (or the status of the consolidation) of the soil deposit can be evaluated. However, no case study has been reported in open literature where the extrapolation method has been applied to estimate unknown stress history of soil deposits. In this paper, this methodology was applied to a dredge disposal area to obtain soil parameters related to stress history as well as soil deformation due to consolidation.

Sediments dredged from harbors and waterways are often contaminated with metal and organic toxins, therefore, their disposal is not only expensive but unsustainable. Treatment and reuse in construction as an alternative to disposal would reduce costs and conserve resources. While thermal treatment followed by carbon adsorption theoretically addresses organics, the fate of metals is of concern. Phosphate addition followed by thermal treatment at 700 °C was investigated for immobilization of metal contaminants with X-ray absorption spectroscopy (XAS). In sediments from Belgium where Zn concentrations were elevated, Zn was precipitated as ZnCO₃ and adsorbed to hydrous manganese oxide and hydrous iron oxide. Phosphate and thermal treatment resulted in sparingly soluble minerals, hopeite (Zn₃(PO₄)₂.4H₂O), and spinels, gahnite (ZnAl₂O₄) and franklinite (ZnFe₂O₄). Leaching assessments with the U.S. EPA toxicity characteristic leaching procedure (TCLP) confirmed Zn and other heavy metals were immobilized. Results of synthetic precipitation leaching procedure (SPLP) showed compliance with the New Jersey State impact to groundwater criteria.

In biroreactor landfills, biodegradation of municipal solid waste (MSW) is accelerated by leachate recirculation. However, the addition of moisture raises stability concerns. Reduced interlocking can also cause stability issues when MSW is shredded before disposing in bioreactor landfills. Engineers usually select safe slopes such as 3H:1V to design above ground MSW slopes in traditional dry landfills. But these slopes may not be safe for bioreactor landfills due to the stability concerns. Use of shallower slopes is not attractive because of the reduction in effective landfill capacity. This paper describes how geogrids may be used to enhance the stability of MSW slopes in bioreactor landfills. A preliminary stability analysis of un-reinforced and geogrid-reinforced MWS slopes was conducted using PLAXIS. The results indicated that the geogrids are capable of improving the factor of safety of MSW slopes. In geogrid-reinforced MSW failure surface developed at the ends of embedded geogrids separating reinforced MSW from un-reinforced MSW. This failure surface was larger than the failure surface developed for un-reinforced MSW. A different failure mechanism triggered when various lengths of geogrid were used. Although large displacements were found near the toe of the slope, a greater factor of safety was obtained.

Building construction on Brownfield sites, especially landfill sites, often requires the design and construction of vapor control systems for the purpose of minimizing the impact of subsurface vapors on building inhabitants. Vapor control systems are typically comprised of active or passive vapor extraction systems, a vapor barrier, and vapor monitoring systems and are integrated with the building foundation system. Integration of vapor control systems with deep foundation systems on settlement-prone subsoils and municipal solid waste (MSW) poses challenges not encountered on typical projects. Specifically, vapor control system elements require detailed design to account for potentially large amounts of settlement. Potential remedies typically involve structurally supporting vapor extraction piping, geomembrane vapor barriers, and subsurface vapor monitoring probes. However, structurally supporting vapor control system elements can be challenging and result in potential post-construction problems. Case histories are presented along with design considerations to avoid damage to the vapor extraction, monitoring, and barrier systems.

A three story hotel in Irving, Texas, home to some of the worst soil conditions in the nation, was underpinned with piers that were belled in the active zone. As a result of errors by the engineer and/or contractor, the piers uplifted and moved the building to extreme deflections that exceeded 8inches. To mitigate the problem, 360 — 18inches diameter x 35feet deep drilled piers were installed under the building in five foot of headroom. Despite the low headroom, the new piers were drilled into gray shale a minimum penetration of 10feet. This process was completed while keeping the hotel in full operation with no interruption in services and minimal effects to the landscaping and appearance.

Chromium ore tailings used as fill material beneath pavements can expand significantly under specific site conditions. However, it has been difficult in the past to simulate this behavior reliably in the laboratory. Column expansion tests in an enriched carbon dioxide environment are found to reproduce expansion and induration of the chromium tailings material similar to that observed in the field. Results demonstrate that expansion pressure and degree of induration as quantified by unconfined compressive strength vary significantly with groundwater pH.

A side by side comparison of straight shafts and augercast piles in expansive clay conditions was evaluated in a research project studied at the University of Texas at Arlington and these results showed the performance of both foundations was similar. There was little difference in axial capacity measurements when drilled shafts and augercast piles were constructed with the same diameter and the length. Capacity predictions with theoretical models showed good agreements with the measured results. Also, these analyses results showed that when augercast piles or drilled shafts were constructed in a clay environment, there is no perceptible difference in the skin friction and end bearing resistance factors when predicting ultimate capacity.

Practicing engineers are at times required to ameliorate or stabilize sulfate-bearing soils that exhibit sulfate-induced heave when treated with lime. Cost effectiveness of stabilization and amelioration techniques can be improved by using geologic models that identify the factors and processes that control the distribution of sulfate through the landscape. The paper describes the use of geospatial data sets, direct measurements of soil conductivity, and geochemical modeling to develop a geologic model of sulfate distribution along the SH-130 corridor in Texas. These geologic models can effectively be used to define the risk associated with sulfate-induced heave in soils that are encountered during construction. The technique can also be used to focus sampling and testing to the high-risk locations and thereby contributing to the economic success of the project. The sensitivity of soils to form ettringite/thaumasite with increasing sulfate concentration can also be evaluated using these geologic models.

There has been much speculation about the ability of lime and cement to diffuse into highly plastic soil and chemically alter the clay minerals thereby reducing the shrink/swell capacity of the soil. This research looks at hydrated lime and type I Portland cement in a manufactured soil to obtain direct evidence of the ability of both lime and cement to diffuse into and chemically alter a clay soil. Natural soils are very complex and stabilizer/soil reaction products are difficult to identify so we chose to manufacture a soil. We manufactured five soil samples composed of pure quartz sand (70 wt. %) and pure smectite clay (30 wt. %). Electron probe microanalyses of thin-sections from the manufactured soil samples show high concentrations of calcium throughout the lime stabilized clay aggregates, but very little calcium penetrated the cement stabilized clay. X-ray diffraction confirmed the presence of smectite (clay) in all samples and suggests more calcium substitution in lime treated samples. Calcium from the lime diffuses into the clay to create a chemically altered clay that is less susceptible to shrinking and swelling. The cement forms a protective coating around the clay aggregates and very little calcium actually diffuses into the clay. Thin-section analysis of samples from an expansive, natural soil stabilized with lime and cement shows identical textures to the manufactured soil samples. This research provides direct evidence of lime and cement stabilization mechanisms in clay-rich soils which will allow engineers to make informed decisions about stabilizer options in soils that exhibit shrinking and swelling.

The elastic moduli of specimens prepared under various compaction conditions were investigated for soaked specimens as well as specimens tested at as-compacted moisture contents. In this paper, the linearly increasing elastic modulus that was defined using a modulus number, K, was determined from the results of oedometer test. The ratios of modulus numbers of unsoaked and soaked specimens, K_DU/K_DS, were seen to vary from about 0.5 to 3. The maximum value for these ratios was observed for the specimen compacted at the lowest water content (4.7%) and high density (1.79 g/cm³).

Construction in karst areas includes the risk of encountering voids in the underlying material. Structures built above voids can experience significant settlement and extensive structural damage. In the most severe cases, the voids may open to the surface, cause catastrophic failure of the structure, and endanger the public. For commercial projects with tight deadlines, identifying potential subsurface voids early in the pre-development stage is critical in being able to provide time for further assessment and for remedial activities to be employed. This paper will be centered on a case study of subsurface voids were identified and remediated on a site planned for the construction of a "Big Box" retail store in Northwest Georgia. The paper will present selected methods for identifying voids and the method selection decision process. It will also discuss the subsequent selection of deep soil compaction grouting to fill the voids, to limit the potential for future karstic effects.

Retaining wall designs most always specify use of drainable granular backfill. However, in actual practice, onsite soils are sometimes used as a cost-saving measure. In North Texas these onsite soils are often expansive cohesive materials. Traditional design using non-expansive cohesive backfill is well established. However, these methods do not consider the lateral swelling pressures that expansive soils exert upon wetting. This paper offers a method for estimating the magnitude of lateral swell pressure that may be exerted on such structures when these materials are used as backfills. In addition, stability analyses results depicting the impact of swell pressures of these materials on calculated Factors of Safety (FS) values for external stability are presented.

Published case histories of expansive soil/rock materials have historically reported the effects of vertical expansion, and the lessons learned from vertical expansion of soil/rock materials are numerous. In this case the abutment walls of the Las Colinas Bridge were constructed using the increasingly popular, top-down construction method which, while facilitating the construction process, restricts lateral earth movement. As a result of restraining the lateral earth movement, high horizontal stresses in the clay shale were transferred to the bridge resulting in significant structural problems in the bridge deck and guard rails. This is a case study of a bridge built over and contemporaneous to the development of the President George Bush Turnpike (PGBT) northwest of Dallas, Texas. The geologic formation that impacted this bridge is the Eagle Ford Group (Eagle Ford) a highly plastic, residual clay soil grading to clay shale at relatively shallow depths. This paper covers the studies of the in-situ lateral pressures using the Marchetti flat plate dilatometer test (DMT) in conjunction with monitoring soil mass movement using inclinometers. The paper compares its findings with information in the literature from studies and research that have experienced comparable lateral earth pressures.

The performance of civil structures constructed on unstable or expansive unsaturated soils can be critically affected by moisture movement through these soils. The unsaturated diffusivity coefficient controls transient moisture flow conditions within a soil in response to total suctions or fluxes imposed at the boundaries of the soil profile. This study adopts and analyzes an approach originally developed by Peter Mitchell for laboratory unsaturated soil diffusion coefficient measurements. The diffusivity coefficients are determined by measuring total suction profiles over time in cylindrical soil specimens. Mitchell's methodology for evaluating the soil moisture diffusion characteristics is simple, economical, and accurate hence it can be used on a routine basis in a geotechnical laboratory. The paper presents diffusivity measurements of high plasticity clays exposed to a relatively constant low relative humidity environment in laboratory. The possible effect of soil sample lengths in determining accurate estimates of moisture diffusivity is also presented.

This paper presented the analysis of a residential building built on expansive soils influenced by the local daily weather conditions and a tree over a period of two years. A recently-developed simulation system was used for the simulation in which the influence of weather conditions on evapotranspiration was evaluated by the FAO 56 PM method, the volume change of expansive soil was simulated by fully-coupled consolidation theory for saturated-unsaturated soils, the soil-structure interaction was simulated by coupled contact elements, and the slab foundation and superstructures were simulated by general shell elements. Different simulation techniques were used to combine all these components into one single system. Simulation results indicated that tree had significant influence on behaviour of residential building built on expansive soils.