Geo-Congress 2019: Earth Retaining Structures and Geosynthetics

A tunnel boring machine (TBM) retrieval shaft was constructed in porous limestone using deep soil mixing (DSM) in Miami, Florida. The retrieval shaft had an inner diameter of 28 ft (8.5 m) and extended to a depth of 87 ft (26.4 m). A 15 ft (4.6 m) thick base plug was constructed to resist the uplift forces at the bottom of the shaft. The design of the shaft was carried out using a three dimensional finite element model. The expected stresses in the soil cement mix shaft walls were initially estimated using analytical closed form solutions. The design was later refined by simulating the construction sequence in a finite element model including staged excavation, back-fill, and tunnel break-in. Quality control tests for unconfined compressive strength and tensile strength were obtained during installation of production DSM columns. The retrieval shaft was instrumented using inclinometers and settlements points during construction to monitor the deformations.

Numerical simulations on a non-symmetric deep excavation in Central Jakarta by hypoplasticity model for clay and Mohr-Coulomb (MC) model are presented in this study. The excavation, with an embankment on one side, was constructed in stiff Jakarta clay using the top-down method. Laboratory and field test results have been collected to calibrate parameters for Jakarta clay. An advance constitutive model, hypoplasticity model for clays (HC model), capable of modeling small strain stiffness non-linearity, recent stress-history effects, and large-strain asymptotic behavior was used in numerical simulations on the excavation in Jakarta clay. A comparison between the HC model and MC model is presented.

Construction of the three-level below-grade space for a new 61-story tower in Boston required excavation to depths of up to 14.3 m (47 ft) and up to 7.6 m (25 ft) below the foundations of an adjacent structure. The excavation removed the stiff clay crust that provides increased lateral wall support and resistance to basal instability. Historically, excavating to this depth for building construction in the Back Bay area of Boston was avoided due to excessive ground movements that tend to occur when the stiff clay crust is removed. To address this problem, concrete lateral support elements (subgrade elements) were installed below the bottom of the excavation prior to mass excavation. During excavation, the subgrade elements limited wall movements, controlled basal heave, and prevented excessive settlement of the adjacent structure. The successful implementation of the subgrade elements was the result of a collaborative effort between the design team, contractor, and the contractor’s geotechnical engineer.

Soil nailing has been widely used as a soil reinforcement technique to retain slopes and walls. In this study, a three-dimensional (3D) finite element (FE) model was developed to simulate the performance of an instrumented full scale soil-nailed wall reported by the French national research project CLOUTERRE. The 3D-FE model better simulated the behavior of the soil-nailed wall compared to two-dimensional (2D) FE models reported in the literature. The 3D-FE model was used to investigate the effects of wall and nail inclinations, nail horizontal spacing, and retained soil properties on the wall performance. The global factor of safety was considerably affected by the nail horizontal spacing and soil friction angle. The top horizontal displacement of the wall was significantly affected by the wall and nail inclinations, soil friction angle, and soil modulus of elasticity. Furthermore, the maximum tensile forces in nails were highly influenced by the wall inclination, horizontal spacing between nails, and soil friction angle.

This paper discusses the design, analysis, and performance of a reinforced concrete diaphragm “slurry” wall temporary excavation support system in South Boston, Massachusetts. The excavation support system was required for construction of two deep below-grade parking garages transected by an existing underground transit tunnel. The excavation was approximately 8.8 m (29 ft) deep for one garage and approximately 14.3 m (47 ft) deep for the other. The excavations were supported with a combination of internal and external bracing. A PLAXIS 2D finite element model using the Mohr-Coulomb constitutive model for soil was used to perform staged construction analyses pre-construction. The model was calibrated post-construction using the hardening soil constitutive model based on field measured displacements from inclinometers. The calibrated model indicated that the hardening soil model provided better agreement with the actual slurry wall displacements and highlighted the sensitivity of the Boston blue clay parameters in the model.

Urban cofferdams are used as temporary earth retaining walls to build the core rigid structure of high rise buildings in modern constructions. These cofferdams are often watertight structures consisting of steel sheet piling and internally braced with concrete or steel ring beams. In this study the nonlinear and time-dependent response of concrete ring beams on the performance of an urban cofferdam is investigated. Inclinometer records showed that low curing times coupled with low site temperatures delayed the full structural resistance of the concrete bracing system, resulting in excessive lateral wall movements. A numerical analysis is carried out to study the effects of curing and time (aging, creep, and shrinkage) combined with excavation-related earth and water pressures. Results obtained from the analysis showed that the proposed model accurately captures the observed performance of the cofferdam. Also, it is concluded in this paper that approximately 30% of the observed maximum lateral movements can be attributed to time-dependent effects of the proposed concrete. Excavation designs ignoring these proposed effects could conceal risks associated with potential damage of nearby infrastructure.

Construction of the Western Ticket Hall at Tottenham Court Road Station (Crossrail, London, U.K.) was a critical path activity in order to prepare the underground space for the arrival of two tunnel boring machines. This has led to the implementation of the observational method design to eliminate the lowest level of temporary propping, resulting in a 13 m prop-free excavation at the bottom of the 30 m deep diaphragm wall station box. The work had led to extensive monitoring of the excavation and the retaining wall measured data is presented in this paper and used to back analyse the most probable geotechnical parameters using the hardening small strain soil model in the Plaxis finite element software. The design of this retaining structure is also used to assess the implications of the ultimate limit state design approach adopted in the U.K. under Eurocode 7 for geotechnical design using finite element method and advanced constitutive soil models.

On March 12, 2015, the runway safety area (RSA) and engineered material arresting system (EMAS) were destroyed when the 73-m (240-ft) high reinforced earth slope failed at Yeager Airport in Charleston, West Virginia. The cleanup and stabilization of the area resulted in the displacement of the Runway 5 threshold and the shortening of the usable length of Runway 5-23. This impacted airline as well as Air National Guard operations. Thus, it was critical to restore safety features and normal operations as quickly as possible once the debris was removed, leaving a temporary 1.5:1 slope. To achieve this goal, a new 122-m (400-ft) long retaining wall up to 25-m (83-ft) high was designed and constructed to meet the difficult site conditions and restore safety features of the runway. To control load magnitudes as well as to facilitate construction, the wall was designed with two distinct sections. The lower portion of the wall was designed to retain compacted soil backfill and be secured to the existing sandstone bedrock with rock socketed steel piles and post-tensioned tieback anchors. This soil backfill establishes a stable 2:1 (horizontal:vertical) slope in the area. The upper portion of the wall was backfilled with up to 17 m (55 ft) of geofoam with a steel post and concrete panel facing. This paper will present an overview of the design and construction challenges posed by the site conditions as well as those associated with bottom-up construction of an anchored soldier pile wall and incorporation of geofoam backfill. Construction was ongoing at the time this paper was completed.

The Philadelphia Museum of Art is a major landmark in Philadelphia, Pennsylvania. In 2000, the Museum of Art Board of Trustees’ Facilities Master Plan outlined a number of improvements, including the “Core Project”, that were initiated in 2012 and broke ground in 2017. The scope of work included a variety of complex geotechnical challenges. Many of these challenges could not be fully defined prior to construction, due to access constraints within the existing museum building. As a result, an observational design approach for both temporary and permanent earth support and foundation modifications was developed during design and implemented during construction. This paper discusses various geotechnical issues, construction related challenges, proposed solutions, and lessons learned upon completion of the project. Key takeaways included the importance of having proper coordination and protocols in place to address changes in the field, utilizing an observational design approach when working below this historic structure, and completing below-grade work while not impacting daily operations of the museum.

Geosynthetic reinforced soil integrated bridge system (GRS-IBS) technology supports prefabricated bridge superstructure elements on geosynthetic reinforced soil bridge abutments. The close spacing of the geosynthetic reinforcement within the abutment increases the confinement and stiffness of the compacted granular backfill, which results in a very strong and internally-supported system. In a similar fashion as other types of reinforced walls, a given GRS-IBS structure should be internally and externally stable under various applied loads such as surcharge, self-weight, and earthquake loads. Both bearing capacity and global settlement analyses of a given GRS-IBS necessitate calculation of the applied bearing pressure beneath the GRS-IBS. However, the actual applied bearing pressure beneath a given GRS-IBS is fairly difficult to determine using traditional design approaches, given the significant eccentricity of the applied load induced by the bridge superstructure, lateral earth pressure, as well as the flexible nature of the reinforced soil foundation (RSF, the most commonly used GRS-IBS foundational support system). The flexible nature of the foundation is a particularly challenging issue, because the deformed shape of the RSF is actually the result of a fairly complicated soil-structure interaction mechanism. Different factors that were explored that can affect the applied stress distribution beneath the foundation include the geometry of the reinforced soil zone in the abutment itself, the reinforced soil zone and RSF foundation strength parameters, the unit weight of soil in the reinforced soil zone, and the rigidity of the connection between the retained and reinforced soil zones and between the reinforced soil and facing zones. The authors will present and discuss the effect of these parameters of interest, using results from a series of finite element numerical simulations.

Contractors are increasingly requesting to use flowable fill (CLSM) or lightweight cellular concrete (LCC) to replace compacted granular backfill at bridge abutments because they can be placed more rapidly. In addition, LCC reduces the settlement of the underlying soils which is attractive to engineers. To evaluate the passive force-deflection curves for these materials, large-scale lab tests were performed with LCC and CLSM backfills in addition to a granular backfill for comparison. The response of the LCC was similar to that of the granular backfill with somewhat higher peak force developing at about 2.5% of the wall height. Although the stiffness was about twice as high as the granular backfill, the post-peak reduction was less than that for the granular fill. In contrast, the CLSM had a stiffness about 10 times higher than the granular fill and reached the peak value at a deflection equal to 1% of the wall height. The CLSM experienced a rapid decease in strength of about 60% after the peak strength was reached. The ductility of the LCC makes it a more suitable material for seismic loading with higher displacement demands.

A mechanically stabilized earth (MSE) structure reinforced with steel soil reinforcements is a flexible coherent gravity mass, sized to resist external loads applied by the retained soil and any surcharge. The structure’s high internal strength and high load-carrying ability derive from the permanent, predictable bond between reinforcements and granular backfill (the reinforced fill), assuring internal stability. The strength and flexibility of an MSE structure make it well-suited to sites where significant settlement is expected. Such sites may require foundation improvement, a costly but effective solution; a less costly solution is to reduce the load applied to the foundation soil by using a lightweight aggregate or low-density cellular concrete (LDCC) as the MSE reinforced fill. The selection of LDCC as the reinforced fill is typically made by the owner or the owner's engineer, not by the MSE supplier. Design and construction of the MSE structure must consider the properties of the selected LDCC product.

This paper summarizes the U.S. Department of Transportation’s Federal Highway Administration (FHWA) experience with the geosynthetic reinforced soil (GRS) integrated bridge system (IBS), an innovative method of bridge support. The range of structure types, sites, and materials that have been used in the deployment of GRS-IBS from 2011 to 2017 are discussed. This paper will also summarize several case histories from around the U.S. where GRS-IBS was constructed for stream, roadway, and railroad crossings. Lastly, the paper will discuss updates that were made to FHWA’s GRS-IBS typical notes and details that will provide opportunities for continued use of GRS-IBS in the future.

In the summer of 2014, in Salem, MA, construction started on a new $1.06 billion high efficiency, natural gas combined cycle power plant capable of generating enough electricity to power over 600,000 homes. Integral to project permitting and incorporating the new energy center into the Salem community, the perimeter of the plant is framed on three sides by an earthen berm supported on the inside by MSE wall with gabion facia, topped with a freestanding gabion wall. The design and construction of the berm faced multiple challenges: the design team had to contend with a project site composed of almost entirely landfill of various vintages and complying with permit design documents to capture the vision originally presented at project conception. The construction team faced the task of coordinating the design across multiple project stakeholders and constructing MSE/gabion wall simultaneously with the earthen berm and storm drainage within a tight corridor surrounding the active power plant project.

Geosynthetic-reinforced soil structure with wrap-around facing has been widely used in civil infrastructures due to its light weight, low cost, and better foundation adaptability. This paper evaluates the performance (including vertical earth pressure, and strain of reinforcement) of a 14-m high geogrid-reinforced slope (0.5-m layer spacing) with an 8-m high embankment as surcharge loading through a numerical model using the fast Lagrangian analysis of continua (FLAC) 3D. The results of the numerical model were then compared with data monitored from a field site (in the same structure) for validation. It was found that the vertical earth pressure increases with the increase of backfill height. The increase amplitude decreases obviously when filling the embankment, indicating that the influence of the upper embankment on the lower reinforced slope is limited. Peak tensile strain of geogrid occurs along the reinforcement layer. The measured and simulated maximum strains are 1.28 % and 0.12%, respectively, which are less than the maximum tensile strain of the geogrid (i.e., 9.5%). Therefore, the geogrid is unlikely to be snapped. The trend of potential slip surface in the field test is consistent with that of the numerical model. However, the potential slip surface of the numerical model moves toward the inner side of the reinforced body, which indicates the slope is in a safe state.

The Center for Community Health (CCH) is the latest addition to New York Presbyterian Hospital’s campus at Brooklyn Methodist Hospital in the Park Slope neighborhood of Brooklyn, New York. The CCH will be housed in a new 7-story concrete and steel-framed building with two deep cellars that occupies a 56,000-square-foot (SF) [5,200-square-meter] U-shaped site across the street from a historic landmark district. Below-grade lot-line construction required excavation up to 50 feet (15 meters [m]) below adjacent sidewalk grade, up to 40 feet (12 m) below adjacent 100-year-old row homes, and up to 25 feet (7.5 m) below the hospital’s adjacent medical office building that remained open throughout construction. Excavation support was provided by a combination of secant pile walls (along adjacent buildings) and soldier piles and lagging (along public sidewalks). Secant piles were drilled using the cased continuous flight auger (cased CFA) and Kelly-Bar drilling techniques. This is only the second time the foundation drilling contractor (Hayward Baker) had used the cased CFA technique in the New York City area. Up to four tiers of lateral bracing were provided using a combination of drilled-in hollow bar tieback anchors and rakers. Strict movement tolerances were implemented to avoid damage to the neighboring buildings during excavation. Monitoring of the adjacent buildings was conducted to verify that building movement was kept within tolerance during excavation and foundation construction. The secant piles installed for excavation support were also used as permanent foundation support for the building. Elsewhere, the building was supported on a mat foundation (for the building core) and spread footings (for individual columns) bearing in the glacial till underlying the site. The secant piles were treated as drilled piles, gaining their support by friction in the glacial till beneath the lowest-level cellar slab. Load testing of the production secant piles was impractical. Axial capacity was verified by 450-ton (4,480 kN) load tests on sacrificial piles in the middle of the site that were drilled in the same manner as the secant piles. Piles were instrumented during load testing to determine the capacity for the portion of the pile below the future basement level. Support of excavation construction was completed within the overall project schedule. No soldier piles needed to be re-drilled, and less than 1.5% of the anchors and secant piles needed to be re-drilled because of installation problems or field conditions. Below-grade construction caused minimal disturbance to the neighboring properties. Lateral movement of the secant walls was less than ¼-inch (6.4 mm), which agreed with the FEM models.

The Skanska/Kiewit/ECCO III team (SKE) in association with HNTB and Haley & Aldrich (HNTB/H&A) was awarded the design-build contract for Phase I of the Kosciuszko Bridge Replacement Project. HNTB/H&A was responsible for design of the Brooklyn connector which includes the construction of new staged filled embankments utilizing prefabricated modular retaining walls (T-Walls). The indicative plans called for the new alignment to be constructed beneath the existing, in-service, column-supported Brooklyn Queens Expressway (BQE) using lightweight fill to avoid potential settlement impacts. The design-build team elected to use normal weight fill which led to unique design challenges of low overhead construction conditions and mitigation of potential construction impacts to the BQE on settlement sensitive shallow foundations. The subsurface investigation undertaken, derivation of soil parameters, and settlement assessment of the soils supporting the existing BQE and the deformation of the viaduct is discussed. A construction monitoring program was used to assess settlement predictions as they relate to the true behavior of the soils and structure.

This paper explains probabilistic analysis and design for simple internal stability limit states for mechanically stabilized earth (MSE) walls using the example of reinforcement pullout of a steel strip reinforcement layer. The general approach uses a closed-form solution for reliability index which is easily implemented in a spreadsheet and thus eliminates the need for Monte Carlo simulation. A novel feature of the formulation is that it includes uncertainty in the choice of nominal values and the underlying accuracy of the load and resistance models that appear in each limit state equation using bias statistics. The paper demonstrates how bias statistics for tensile load and pullout model accuracy can be gathered from load measurements recorded from instrumented walls and found in laboratory pullout box test databases. The concepts are general and can be applied to any soil-structure interaction problem which can be expressed by a simple linear limit state performance function and for which bias statistics are available.

The design of mechanically stabilized earth (MSE) walls requires that the reinforcement have enough strength to resist lateral earth pressures due to the retained soil. The maximum load on the reinforcement is often assumed to be a function of the lateral earth pressure and the reinforcement spacing; however, case histories have shown that the load at the face is smaller than the theory suggests, particularly for closer spaced reinforced soil systems. A common method of measuring lateral earth pressures against the face of a modular block wall is with contact pressure cells (CPCs). As another alternative, this paper evaluates the use of tactile pressure sensors (TPSs) to measure lateral pressure behind the face of a block, in terms of the total stress and its distribution across a surface of the sensing mat. In this study, a CPC and TPS were both placed behind a facing block of two different geosynthetic reinforced soil (GRS) piers: one constructed with open-graded backfill and the other with well-graded backfill to measure the lateral earth pressure against the face throughout the course of the load test to failure. This paper provides an overview of the TPS technology, its calibration, and method of use for this application, along with a discussion about its potential benefits and limitations. The paper also provides a comparison between TPS and CPC results during the load tests. The findings from both sensors indicate that the measured lateral pressure against the back of the facing was considerably less than that typically assumed in MSE design.

Geosynthetic reinforced soil-integrated bridge systems (GRS-IBS) are increasingly being used for rapid, cost-effective construction of bridges. This system works by constructing a geosynthetic reinforced soil abutment on the native material and an integrated bridge approach which can reduce differential settlement between the abutment and approach road. Recently, the first GRS-IBS was constructed in the state of Alabama, located on Turkey Creek, in the Sand Mountain region of Marshall County. Two 3.6-m (11.72-ft) high GRS-IBS abutments were constructed on native Pottsville sandstone. The site was monitored during construction and continues to be surveyed to measure any movement of the abutments. The abutments were also instrumented with pore pressure transducers and earth pressure cells to monitor any change in in situ stresses. This paper provides an overview of the construction of the bridge and describes trends observed in the monitoring data. Lessons learned during the construction process and suggestions for future projects are discussed.

A 210-meter-long (700 ft), 7.3-meter-high (24 ft) embankment constructed over soft ground experienced excessive deformation during and following construction. More than 120 m (400 ft) of the embankment is constructed with back-to-back, near-vertical, mechanically stabilized earth walls (MSEWs). The embankment was constructed to replace an existing single-track railroad bridge and trestle structure with two tracks that are supported on the embankment. Pile foundations of existing structures removed to facilitate embankment construction were cut off about 600 mm (2 feet) below the ground surface and left in place. The MSEW embankment was partially supported on soil, partially constructed over the abandoned railroad bridge and trestle foundation elements, and partially constructed over new pile-supported structures below and within the embankment. The variable foundation conditions resulted in differential settlement, embankment rotation, cracks forming in the embankment top, and distortion of the railroad tracks, including significant distortion within the switches of the double crossover that made the switches potentially inoperable. Although the tracks were opened for 4 months immediately following construction, their use was temporarily discontinued for a 10-month period during which stability improvement measures and an embankment monitoring program were implemented. Maximum settlement at the wall face after 2 years exceeded 850 mm (34 inches). Maximum outward rotation (reverse batter) of the wall face exceeded 460 mm (18 inches). Repairs included installing 181, 610-mm-diameter (2 ft), reinforced auger-cast piles along the MSEW wall toe, and constructing a pile-supported concrete cantilever retaining wall in front of portions of the MSEWs. This paper presents and discusses the project history, subsurface conditions, MSEW embankment construction, embankment distress, monitoring program, repairs implemented, and lessons learned.

Flood walls are specific types of retaining walls that, in addition to the usual and seismic loadings, are subjected to hydraulic loadings such as flowing water, submergence, and wave action. The current practice for structural design of flood walls has mainly focused on estimating the material properties and dimensions of the structure based on the U.S. Army Corps of Engineers design manuals. Although these could ensure the safety of the structure; the design process typically adopts a trial-and-error procedure; therefore, the final design could be non-optimal and expensive. In this paper, an optimum design procedure based on non-dominated sorted genetic algorithm II (NSGA-II) technique is developed for multi-objective design optimization (MODO) of flood walls. The procedure simultaneously minimizes the cost and weight of the structure, while satisfying the stability and ultimate limit state constraints. As an illustration, the developed procedure is used for an optimum design of an inverted T-type flood wall with and without considering a shear key subjected to two different load conditions. Lastly, a parametric study is conducted to evaluate the influence of soil properties and freeboard on the optimum design results.

This paper presents a case history of an urban re-development project in Boston, Massachusetts, where multiple foundation types were used to overcome the unique geotechnical and environmental subsurface conditions present at the site. The project site is located on a hilltop adjacent to a hospital and a high school. The majority of the site has a thin layer [1 m (3 ft)] of fill overlying shallow glacial till deposits. However, there are areas of the site where the fill is up to 8.8 m (29 ft) thick and contains debris including asbestos containing materials (ACM). To allow for the construction of two of the planned buildings over the deep fill areas, a hybrid foundation solution was proposed, consisting of drilled micro-piles and shallow foundations constructed both on natural soils and on the existing fill following the installation of ground improvement. In addition, a variable-height permanent soldier pile and lagging retaining wall was required to achieve the planned site grades.

The present study investigates the efficacy of geosynthetics in improving the performance of machine foundation. A series of block resonance tests were conducted over the soil beds reinforced with the different type of geosynthetics. Three different cases, namely, unreinforced, geogrid reinforced, and geocell reinforced cases were considered. The experimental results have shown that the performance of geocell is more effective than geogrid and unreinforced conditions. In the presence of geocell, the displacement amplitude and peak particle velocity were reduced by 53% and 46% respectively, as compared to the unreinforced condition. Similarly, the maximum improvement in resonant frequency of the unreinforced soil bed was observed in the presence of geocell reinforcement. Further, the resonant frequency obtained from the field study was compared with the analytical solution derived from mass spring dashpot model. The resonant frequency obtained from the analytical solution has shown good agreement with the frequency obtained from the experimental study.

Management of the earth structures is important to ensure proper functioning of roads. Given that Japan is home to many earth structures, the basic premise of earth structure management is to prevent traffic hazards by conducting regular inspections. New inspection methods are required to reduce the use of human resources involved in earth structure management. This article discusses the applicability of mobile photogrammetry to the inspection of reinforced soil walls. A photogrammetry tool was fixed to a vehicle to measure the surface geometry of the target. The test wall was an 8.0-m high geogrid reinforced soil wall. Mobile photogrammetry data were validated by comparing the measurements obtained using the proposed method and a classical total station. The results of the mobile photogrammetry field test showed that when the speed of the mobile photogrammetry vehicle was 0 or 30 km/h, measurement errors decreased with increase in the number of pictures used in the analysis. Mobile photogrammetry results using six pictures were less affected by vehicle speed. These results support the use of the proposed system in future inspections of earth structures.

Mechanical properties of recycled concrete aggregate (RCA) and recycled asphalt pavement (RAP) were evaluated for use as backfill in mechanically stabilized earth (MSE) walls. Large scale triaxial compression tests, interface direct shear tests, and pull-out tests were conducted to evaluate interaction of RCA and RAP with geosynthetics. Consolidated drained triaxial tests under sustained axial stress were conducted to evaluate creep potential of compacted RAP. Results show the compacted RCA and RAP samples tested herein have internal friction angles (ϕ') of 47^o and 29^o respectively which are within the typical range of ϕ' reported in the literature. Both RAP and RCA exhibited a higher interface friction angle (δ') with geogrids than with geotextiles. No slippage was observed between the RCA-geotextile and RCA-geogrid and the failures were due to rupture of the geotextiles and geogrids during the pullout test. RCA has higher interaction coefficient (C_i) with geosynthetics than RAP. The interaction coefficients for both RCA and RAP increase with normal stress. Results from creep tests showed that compacted RAP exhibits large deviator strains under sustained deviator stresses. Use of RAP and RCA in MSE walls are recommended if reinforced with geogrids only. To prevent creep failure of compacted RAP, maximum deviator stress in the backfill should be limited to 80% of compressive strength of compacted RAP.

This paper describes the results of laboratory study on pullout behavior of a polyester geogrid embedded in pond ash. The objective was to assess the feasibility of utilization of ash available in abundant quantity at thermal power plants as a fill material in reinforced soil structures (RSS). The ash does not satisfy the gradation requirements but satisfies the physical and shear strength properties recommended for use in RSS by FHWA and BS:8006. Pullout tests were then carried out as per ASTM D6706 at three normal stresses of 20 kPa, 40 kPa, and 80 kPa. The obtained results were then compared with those of geogrid embedded in reference fill material, Yamuna sand. The study reveals that although pond ash does not satisfy the gradation requirements of a suitable backfill material, the pullout resistance offered by geogrid embedded in pond ash was almost identical to that in sand.

Stone columns are commonly used for ground improvement in soft soils. In very soft soils, insufficient soil strength for the soil surrounding the upper portion of the column often causes lateral bulging failure in this zone when the column is loaded, even at relatively small applied vertical stresses. To prevent this type of failure, stone columns can be encased using a high strength geosynthetic; this encasement increases the overall strength and stiffness of the stone column and prevents lateral bulging of the column into the surrounding soft soil. Encased stone columns can be used for foundation support applications or for large-area ground improvement, and show potential utility for the support of road embankments, oil storage tanks, and other types of structures that are not overly sensitive to settlement. In certain field cases, the soft soil layer can be thick, making the construction of the encased stone column down to a hard bearing layer impractical. This study describes the results from three-dimensional finite element analyses that were carried out to analyze the behavior of a single fully encased stone column resting on a non-rigid layer that is subjected to load on the top of the stone column. The numerical modeling that was performed studies the influence of varying the: dilation angle of the stone column material, diameter of the encased stone column, tensile strength of the encasement, and depth of the soft soil beneath the tip of the encased stone column (i.e. floating depth). These parameters play an important role in the behavior of the stone column in both the elastic and plastic phases of deformation. The numerical analyses show that the column diameter has a significant effect on the bearing capacity and load-displacement response of the encased stone columns. Also, the bearing capacity of the encased stone column tends to have a high correlation with decreasing “floating depth”.

A new woven geotextile with wicking fibers (also named as “wicking fabric”) has been recently developed to deal with excess water within pavement structures. The wicking fibers have specially designed deep grooves that can maintain saturated to hold and transport water under unsaturated conditions. Both laboratory and field tests have proven the effectiveness of the wicking fabric in dehydrating the road embankment. In the engineering applications, the wicking fabric was exposed to the surface of the road embankment for the water evaporation purpose. The long-term drainage performance of the wicking fabric may be influenced by such potential issues as the permanent deformation, clogging, salt concentration, and mechanical failure of the wicking fibers. To evaluate the long-term drainage performance of the wicking fabric, samples were collected from a field test section. A scanning electron microprobe (SEM) was used to analyze the severities of the potential issue. Test results indicated that the permanent deformation is expected in the wicking fabric. However, the wicking fabric can still work effectively to wick water out of pavement structures.

In the present paper, laboratory-scale experimental investigation has been carried out to study the effect of footing interference on bearing capacity improvement and settlement reduction of two closely spaced identical footings resting on unreinforced and geogrid-reinforced sand layer of limited thickness underlain by a soft clay layer. The effect of aspect ratio of footing on bearing capacity improvement and settlement reduction for interfering footings is also studied. At S/B=2 (where S is the spacing between the interfering footings), higher values of bearing capacity ratio (BCR), improvement factor (I_f), and settlement reduction factor (SRF) are observed for interfering footing compared to isolated footing. Further, it is observed that the magnitude of BCR, improvement factor, and settlement reduction factor decrease almost linearly with an increase in aspect ratio (L/B ratio) which indicates that BCR, I_f, and SRF decrease from square footing to strip footing.

This paper presents multi-layer interface shear test results for composite liner systems from fourteen landfill projects in California. The multi-layer configuration utilizes site-specific materials including low-hydraulic conductivity compacted soil (CSL), geosynthetic materials [geosynthetic clay liner (GCL), geomembrane (GM), drainage geocomposite (GC), and geotextile (GT)], leachate collection and removal system (LCRS) gravel, and/or protective cover soil (PCS), as applicable. This paper describes the test configuration and test procedures to represent field configurations, including soaking and saturation conditions, choice of normal stresses, and California Water Board recommended procedures for calculating shear strengths for encapsulated GCLs. The importance of simulating field conditions is discussed. In addition, a comparison was made between results from single and multi-layer interface tests for two of the projects. This paper also includes a discussion of pros and cons of multi-layer interface tests compared to single interface tests.

The objective of this study was to evaluate the effects of (i) geosynthetic clay liner (GCL) peel strength, (ii) geotextile type, (iii) geotextile mass per area, and (iv) textured geomembrane (GMX) spike density on the critical shear strength (τ_cr) of GCL/GMX composite systems. Displacement-controlled internal and interface direct shear tests were performed with two needle-punched reinforced GCLs (NP GCLs) and two GMXs. The τ_cr of the NP GCL/GMX composite systems increased with an increase in GMX spike density and an increase in mass per area of the GCL geotextile. The effect of geotextile type was noteworthy considering that τ_cr of a composite system consisting of a high-peel strength NP GCL with woven geotextile was lower than τ_cr of a composite system with a low-peel strength NP GCL and non-woven geotextile.

Accelerated creep and stress relaxation laboratory tests based on the time-temperature superposition method were carried out on one type of polypropylene (PP) geogrids. The stresses or strains in the tests were maintained at low levels to simulate in-service conditions. The relationships between the long-term stiffness and logarithmic time at different stress or strain levels were obtained. Both the long-term creep stiffness formula and stress relaxation stiffness formula were derived from the test results. By establishing numerical models of geosynthetic-reinforced-soil (GRS) retaining walls with the aforementioned long-term stiffness formulas, the influence of long-term stiffness on the reinforcement load and lateral facing displacement was analyzed by the iterative method. Numerical simulation results showed that the overall reinforcement load decreased with the reduction of long-term reinforcement stiffness, and the lateral facing displacement increased with a decrease in the long-term stiffness. It was found that the creep and stress relaxation responses co-existed and interacted with each other during the normal service life of the retaining walls, and the actual reinforcement load was between the result obtained using only the creep or stress relaxation stiffness, but their differences were not significant. The iterative method proposed in this study could be employed to analyze the long-term reinforcement load of GRS retaining walls.

Geosynthetic drainage composites consisting of a polymer drainage core with geotextiles usually bonded to one or both surfaces. They first appeared in the 1970s, and now see widespread use in a number of different applications. Product differences are particularly in the drainage cores. Two different core types are available: geonets and geospacers. Other than obvious physical differences, they vary greatly in the compressive strengths and in-plane flow rates. These variations are shown by way of test method results in the context of a design graph illustrating eight different products in nine different applications. Regarding field installation, proper procedures are illustrated and are generally practiced accordingly. One issue, however, appears to be lacking. That is the design and maintenance of a proper long-term exit strategy of liquids flowing from the drainage core. Three case histories are presented wherein long-term clogging has occurred resulting in water-filled core situations leading to hydraulic induced failures.

Application of electromagnetic heating has been primarily focused on the biomedical area (e.g., hyperthermia therapy), which has recently extended to environmental and petroleum engineering fields. In the meantime, conventional soil heating, often a preferred option for a number of practical applications such as remediation, fertilization, and sterilization, has been carried out by the installation and operation of the heating source and the heat transfer system. In this background, as an innovative and simple soil heating method, electromagnetic soil heating is investigated in this study. The magnetic nanoparticle-coated geotextiles were prepared via the chemical co-precipitation method to synthesize magnetic nanoparticles and to coat them onto the geotextile simultaneously during the nanoparticle synthesis process. An immediate electromagnetic heating of the magnetic nanoparticle-coated geotextile ascertained the successful coating of magnetic nanoparticles. The prepared geotextile was then inserted into a soil medium, and then exposed to the alternating magnetic field that is generated by the induction heating coil. As a result, a noticeable temperature increase in the soil medium (6~7°C) was observed over a short period of time (5 min). A similar heating rate was observed for both sand and clay specimens. The heat transfer to the surrounding soil functions to prevent a drastic heating of geotextile, which helps to not only warm up the surrounding soil but also hinder any mechanical deterioration of the geotextile. Moreover, experimental results show that the heating performance was independent of the rinsing step, which suggests the fixation of magnetic nanoparticles on the geotextile is robust. Supporting numerical simulations suggest that the magnetic nanoparticle-coated geotextile heated up approximately with the rate of 65 W in the experimental setup of this study, which resulted in ~10°C and ~6°C temperature rise in the geotextile and middle of soil specimen, respectively. Such an innovative heating method can potentially provide additional functionality to geotextiles as an attractive option for soil heating.