Journal of Geotechnical and Geoenvironmental Engineering

Data from bench-scale composite liner experiments were compared with predictions made with two models, a finite-difference model and a semianalytical model, used to predict volatile organic compound (VOC) transport through composite liners. Transport parameters for the geomembrane and clay for five common VOCs were measured independently and used as input. Predictions from both models for all five VOCs were essentially identical. Excellent agreement was obtained between the predicted and measured concentrations for all five VOCs without model calibration. However, inherent variability in measured transport parameters has a significant effect on predictions. Volatile organic compound concentrations in the clay liner near the geomembrane-clay interface depend primarily on transport parameters for the geomembrane. However, this becomes less significant as the distance from the geomembrane-clay interface increases.

The Deer Track Bioreactor Experiment (DTBE) was a field-scale experiment conducted in a drainage lysimeter (8.2-m height, 2.4-m diameter) to assess the physical, chemical, and biological response of municipal solid waste with leachate addition. The experiment was operated for 1,067 days, with leachate dosing initiated on Day 399. Fresh leachate collected from a full-scale landfill was used for each dose. The ratio of cumulative leachate effluent to influent volume increased during dosing and leveled off at approximately 80%, indicating field capacity was achieved. Peak Darcy flux ranged from $2\times {10}^{-7}\mathrm{m}/\mathrm{s}$ to $4\times {10}^{-5}\mathrm{m}/\mathrm{s}$, with larger flux computed for the last four doses when waste saturation was higher. During the experiment, the average dry unit weight of the waste increased 28% and the dry-weight water content ($w_d$) increased 18%; field capacity of the waste was 44 to 48% on a dry-weight basis. Biochemical methane potential decreased from 51.4 to $3.4\mathrm{mL}\mathrm{\text{-}}\mathrm{C}{\mathrm{H}}_4/\mathrm{g}$-dry, indicating that 93% of the potential methane embodied in the waste was removed. The pH of the effluent increased, whereas biochemical oxygen demand (BOD), chemical oxygen demand (COD), and BOD:COD all decreased during dosing. Immediate compression occurred for 1–2 weeks following waste placement, and the immediate compression ratio $C_c^{\prime }$ was 0.23. The average rate of time-dependent compression ($C_{\alpha }^{\prime }$) ranged between 0.048 and 0.35 and varied systematically with waste temperature (increasing $C_{\alpha }^{\prime }$ with increasing temperature).

Wrinkles are buckles or waves that develop from restrained thermal expansion when the geomembrane is left exposed to solar heating. Wrinkles can substantially reduce the effectiveness of the geomembrane as a hydraulic barrier if a hole is at or near a wrinkle, depending on the number, length, and width of wrinkles. Low altitude aerial photography and digital image analysis are used to quantify the nature and extent of wrinkles that developed over one hot and sunny day in a smooth, black, 1.5-mm-thick high-density polyethylene (HDPE) geomembrane over a 55 m by 140 m area. Wrinkles were found to significantly vary over the course of the day, increasing from the fewest wrinkles in the morning to a maximum just after noon before decreasing toward the late afternoon. For the specific conditions examined, wrinkles were found to occupy 3%, 21%, and 7% of the entire area surveyed at 8:45, 12:25, and 17:15, respectively. Connections between adjacent wrinkles were observed to create significant interconnected wrinkle features greater than 2,000 m long. The shortest maximum interconnected wrinkle feature of $80\mathrm{m}/\mathrm{ha}$ was measured at 8:45 while the longest such feature was $6,600\mathrm{m}/\mathrm{ha}$ at $13:45$. The observations and results provide data to support the approach that limiting the time of day when cover is placed on geomembrane can be effective at reducing the extent of wrinkling.

The use of vacuum as a preload together with vertical drains to reduce postconstruction settlement and increase the shear strength of soft ground is increasingly popular. However, conflicting views concerning preloading by vacuum consolidation continue to be disseminated. A review and interpretation of case histories of vacuum loading together with vertical drains indicates that (1) with a novel definition of excess pore-water pressure, existing theories of consolidation, solutions, and associated computer programs that have been developed for fill loading can be applied without any modification to vacuum loading; (2) vacuum that is available in the drainage blanket remains constant with depth within the vertical drains; (3) for vacuum loading as for fill loading, vertical drains may display well resistance; (4) there is no difference in magnitude and rate of settlement for a vacuum load and an equivalent fill load; (5) all empirical concepts of undrained shear strength that have originated from fill loading of soft ground are equally applicable for vacuum loading; (6) a correlation between vertical settlement and horizontal displacement for vacuum loading is expected because both result from consolidation; and (7) preloading by vacuum is accomplished in a shorter period because there is no possibility of undrained failure during vacuum loading, whereas fill loading may require construction in stages to avoid undrained bearing-capacity failure.

Millions of square meters of mechanically stabilized earth (MSE) retaining walls are constructed annually in the United States. For highway applications, a roadside barrier system is placed at the edge of the wall. This barrier system generally consists of an $L$-shape concrete structure so that if a vehicle hits the vertical part of the $L$ shape (barrier), the horizontal part of the $L$ (moment slab) provides the resisting moment during the impact. This impact must be resisted by the soil, the reinforcement, and the panels in the MSE wall. This paper gives guidelines on how to design the reinforcement for pullout and yielding and the panels for flexural and shear failure. It also gives the guidelines on how to ensure the stability of the barrier. These design guidelines are developed in terms of AASHTO load and resistance factor design procedures. In a second part, a full-scale crash test on an instrumented 2.79 m high MSE wall is described and analyzed. The wall and barrier behaved very satisfactorily and represented a verification of the proposed guidelines. Pressure distributions are presented for designing the top two layers of wall reinforcement to resist barrier impact forces. A 44.5-kN static equivalent load is recommended for evaluating the stability of the barrier and moment slab system.

In this paper a knowledge-based clustered partitioning technique is developed for determining reliability index and failure probability of rock wedge. Here, the a reliability index is analyzed and the optimization is carried out using a knowledge-based clustered partitioning (KCP) technique. The reliability index computed with this KCP technique is compared with those using other approaches such as the Excel Solver-based method. The new technique for determining the reliability index involves a global search method and is found effective and efficient. Reliability analysis with this KCP technique is then used to examine the influence of parameter uncertainties and correlations among the parameters on the failure probability of rock wedges. Significant findings are derived from the sensitivity and parametric analysis.

Although a variety of methods exist to estimate axial capacity for augered cast-in-place piles, they are generally limited to allowable stress design (ASD) procedures, with little consideration of design reliability. This paper describes the addition of static loading test results to a global augered cast-in-place pile data set to assess the accuracy of new and existing design methods and to address the current lack of reliability-based design methods for augered cast-in-place piles. The new static loading tests in western Washington were carried out on piles installed in granular materials, with pile diameters and lengths ranging from 0.41 to 0.51 m and 9.5 to 29 m, respectively. The preparation of beta coefficients and unit toe bearing resistance values is discussed within the framework of strain-dependent composite tangent moduli and observed residual loads. New relationships for the beta coefficient and toe bearing resistance values are proposed, and the accuracy of new and existing design procedures is statistically characterized using the updated global data set. Resistance factors for axial compression and uplift are calibrated at the strength limit for use in load and resistance factor design (LRFD).

The soil cement deep mixing method has been used to improve soft clayey soils under embankment loading conditions. A compacted granular fill layer or geosynthetic reinforcement layer is placed over the top of soil cement deep mixed (DM) columns to reduce differential settlement between DM soil and the surrounding untreated soil, which, in turn, increases embankment stability. Typically, in conventional deep mixing methodology, the soil cement columns are closely spaced, indicating large area replacement ratios in the construction projects. Such practice could increase construction costs substantially. In this research, a new type of DM column, called a $T$-shaped DM (TDM) column, was designed and used as an alternative to the large-area-replacement-ratio DM columns employed in the field. Unlike in the conventional column, the cross section of the new column varies along the installation depth. Large amounts of cement slurry are injected and thoroughly mixed with the native shallow soil using specially designed mixing blades. At greater depths, deep mixing methodology is applied only to smaller-diameter columns, resulting in large-diameter columns near the surface and smaller-diameter columns deeper. Field trials were conducted to investigate the performance of TDM column–supported soft ground under embankment loading. For comparison, performance of conventional DM column–supported soft ground under similar embankment loading is presented. Differences in quality control studies and in situ plate loading tests on TDM and conventional DM columns are discussed. Under field embankment loading conditions, stress concentration ratio, excess pore water pressures generated in the soft clays, total monitored settlement, and lateral soil displacement near embankment toes are analyzed and discussed for both treatments. It is concluded that TDM columns have considerable advantages over conventional DM because they both mitigate settlement and enhance the performance of the embankments while reducing construction costs.

This paper presents an experimental investigation on soil deformation around uplift plate anchors in sand by using digital image correlation (DIC). The experimental setup consists of a camera, loading frame, plexiglass mold, and computer, which is developed to capture soil deformation during anchor uplifting. A series of model tests are performed to investigate the influence of particle size, soil density, and anchor embedment depth on soil deformation. A set of images captured during anchor uplifting are used to calculate soil displacement fields by DIC. The failure surface is studied by tracking the points with maximum shear strain values. On the basis of this study, it is found that soil deformation and the pullout resistance of plate anchors are substantially influenced by soil density and anchor embedment depth, whereas particle size within the studied range has limited influence. In dense sand, the shape of the failure surface changes from a truncated cone above a shallow anchor to a combined shape of a curved cone and a truncated cone for a deep anchor. In contrast, in loose sand a cone-shaped failure surface is formed within the soil mass above a shallow anchor; however, no failure surface is observed for a deep anchor, where the compressibility of soil is the dominating factor that influences the behavior of deep plate anchors in loose sand.

An in situ test program was undertaken to systematically investigate the effectiveness of the heavy compaction method (HCM) normally used for sandy soils for compacting fly ash deposit. Measurements of soil performance and cone penetration tests before and after the compaction were carried out, indicating obvious effects on soil properties and strength increase in the improved ground. It has been found that HCM introduces three-dimensional (3D) nonuniformity in the upper part versus horizontally uniform layers in the lower part of the improved ground. Also found is that the HCM-induced vertical soil strain is almost proportional to the ratio of cone resistance increment to the prior-treatment cone resistance in the uniform zones.

The objective of the study presented herein is the development of an understanding of the influence of non/low-plastic fines and associated aging effects on the penetration resistance ($q_t$) and liquefaction resistance ($R_L$) of sandy soils. Towards this end, the authors performed a series of cyclic triaxial tests on samples having varying relative densities ($D_r$) and fines contents ($F_c$), wherein a miniature cone was incorporated into the triaxial apparatus. This allowed the penetration resistance and the liquefaction resistance to be determined directly for the samples. To simulate geologic aging effects, a small amount of cement was mixed in with the soil during sample preparation. From “unaged samples” without cement, it was found that although both $R_L$ and $q_t$ decrease as $F_c$ increases, a unique relationship exists between $R_L$ and $q_t$ that is independent of $F_c$. However, from samples having the same $C_c/F_c$ (i.e., simulating the same geologic age), it was found that $R_L$ increases as $F_c$ increases for the same $q_t$. This trend is consistent with field-based $R_L\mathrm{\text{-}}{q}_t$ correlations for natural soil deposits to which aging effects are intrinsic. Thus, it has been clarified that it is not the $F_c$-value by itself but rather the cementation effect associated with higher $F_c$ that results in a higher liquefaction resistance for a given $q_t$.

Compressibility of a soil mass is among the most important geotechnical properties that is widely used during the design of geotechnical structures. Various regression equations have been proposed by numerous researchers in the past to estimate the compression index of a soil specimen with parameters such as void ratio at liquid limit, initial void ratio, liquid limit, or the combination of the specific gravity, void ratio, and liquid limit. Although all researchers concur that the compression index depends on the mineralogical composition of the soil and initial moisture content, very little research has been performed on the mixtures of minerals composing a wide range of activities under consistent initial moisture contents. This research is conducted on 55 different soil specimens prepared in the laboratory by mixing various proportions of montmorillonite, illite, kaolinite, and quartz at initial moisture contents equal to the liquid limit. The intrinsic compression line (ICL) was unique for most of the mixtures used for this study. Very good regressions were obtained between the compression index and initial void ratio, initial porosity, plasticity index, or liquid limit. Two different equations were proposed to estimate the compression indices of remolded clays with liquid limit—one for soils with activities less than one and the other for soils with activities greater than one. The compression indices of 82 different natural samples, reconstituted at liquid limit, were similar to the values estimated with the proposed equations. Furthermore, the compression indices of the soil samples presented in the literature could also be estimated with reasonable accuracy using the proposed equations.