Journal of Geotechnical and Geoenvironmental Engineering

Two soil-bentonite cutoff-wall backfills obtained from construction sites, one in New Jersey and one in Delaware, were tested for the existence of membrane behavior. Both backfills were designed as a mixture of dry bentonite (3–4% by dry weight) and the locally excavated soil blended with bentonite water slurry to provide slumps ranging from 100 to $150\mathrm{mm}$ (from 4 to $6\mathrm{in}.$ ). The results of the membrane tests indicate that both backfills exhibit membrane behavior. Further, the magnitude of the membrane behavior increases with decreasing void ratio. However, the magnitude of the increase in membrane behavior in these construction-site backfills was lower than that previously reported for model backfills prepared in the laboratory. The difference in the membrane behavior is attributed, in part, to a lower percentage of clay in the construction-site backfills relative to the model backfills. Nonetheless, based on the measured membrane efficiencies for the two field-constructed backfills, the total liquid flux $\left(q\right)$ through the cutoff walls can be expected to be reduced relative to that in the absence of membrane behavior $\left(q_h\right)$ by 1–10% for the cutoff wall in Delaware and 7–8% for the cutoff wall in New Jersey, depending on the void ratio. Thus, the results of this study suggest that membrane behavior in field-constructed cutoff walls can be significant, depending on the void ratio and the clay content of the backfill.

The unit weight of municipal solid waste (MSW) is an important parameter in engineering analyses of landfill performance, but significant uncertainty currently exists regarding its value. A careful review of reliable field data shows that individual landfills have a characteristic MSW unit weight profile. Based on in situ unit weight data and trends observed in large-scale laboratory tests, a hyperbolic relationship was developed to represent this characteristic MSW unit weight profile. Within the context of this characteristic profile, landfill-specific values of MSW unit weight depend primarily on waste composition, operational practices (i.e., compaction, cover soil placement, and liquids management), and confining stress. Guidance is provided for developing landfill-specific MSW unit weight profiles, including procedures for performing large-scale tests for in situ measurement of MSW unit weight at a landfill.

To investigate group interaction effects as a function of pile spacing, full-scale cyclic lateral load tests were performed on pile groups in stiff clay spaced at 3.3, 4.4, and 5.65 pile diameters in the direction of loading with as many as five rows of piles. Group interaction effects decreased considerably as pile spacing increased from 3.3 to $5.65D$ . Lateral resistance was a function of row location in the group, rather than location within a row. For a given deflection, the leading (first) row piles carried the greatest load, while the second and third row piles carried successively smaller loads. Fourth and fifth row piles carried about the same load as the third row piles. For a given load, the maximum bending moments in the trailing row piles were greater than those in the lead row, but these effects decreased as spacing increased. Cyclic loading reduced the peak load by about 15% after 15 cycles; however, distribution of load within the pile group was essentially the same as at the peak load. Gaps significantly reduced resistance for small deflections.

Using the results from three full-scale lateral pile group load tests in stiff clay with spacing ranging from 3.3 to 5.65, computer analyses were performed to back-calculate $p$ multipliers. The $p$ multipliers, which account for reduced resistance due to pile–soil–pile interaction, increased as pile spacing increased from 3.3 to 5.65 diameters. Extrapolation of the test results suggests that group reduction effects can be neglected for spacings greater than about 6.5 for leading row piles and 7–8 diameters for trailing row piles. Based on analysis of the full-scale test results, pile behavior can be grouped into three general categories, namely: (1) first or front row piles; (2) second row piles; and (3) third and higher row piles. $p$ multiplier versus normalized pile spacing curves were developed for each category. The proposed curves yield $p$ multipliers which are higher than those previously recommended by AASHTO in 2000, the US Army in 1993, and the US Navy in 1982 based on limited test data, but lower values than those proposed by Reese et al. in 1996 and Reese and Van Impe in 2001. The response (load versus deflection, maximum moment versus load, and bending moment versus depth) for each row of the pile groups computed using GROUP and Florida Pier generally correlated very well with measurements from the full-scale tests when the $p$ multipliers developed from this test program were employed.

This paper presents a study of ochre formation in geotextile filters. Ochre is a substance found sticking to solid surfaces of drainage systems that may cause clogging. The accumulation of such materials in a drainage system may have undesirable implications, such as a decrease in drainage flow capacity and an increase in soil pore pressure; instability of soil masses and retaining systems; and alteration of the direction of flow and development of pipes. Ochre formation is the result of microbial activities on iron compounds naturally found in seepage water. Even though geotextiles have been widely used in drainage systems, very few studies have considered ochre formation in the tests. Laboratory column filter tests were conducted to simulate the ochre formation process under similar conditions to those in geotechnical works and to assess the long-term performance of a geotextile. Ochre is most likely to be formed at an aerated/nonaerated interface in the filter. In order to obtain this condition, the underneath face of the filters was opened to the atmosphere. Three different types of geotextile—nonwoven polyester, nonwoven polypropylene, and woven polypropylene—were used in the tests. Control tests were also conducted with a sand filter to provide a basis for comparison. Hydraulic conductivity changes and iron retention within the permeameters were monitored throughout the tests. Ochre was formed under the presence of iron ions and iron bacteria. During the test period, the filters were not clogged to such an extent as to induce a global reduction in the permeability of the drainage system. Nevertheless, at the end of the tests a considerable amount of ochre was found in all filters and there was a significant variation in the permeability of the geotextile filters when tested in isolation. These studies may contribute to discovering whether ochre can be considered as a biofilm, evaluating the clogging potential and defining mitigating measures.

A new approach for estimating the susceptibility of a layered, liquefiable, infinite slope to shear deformations associated with void redistribution is presented. The excess pore water pressures associated with liquefaction produce upward seepage within the slope. The lower portion of a liquefied layer expels a certain volume of pore water, $V_{\mathrm{con}}$ , as it contracts (densifies). If the liquefied layer is overlain by a lower permeability soil, then the pore water expelled from the lower contracting zones can become trapped causing void ratio increase in a dilating sublayer near the interface, reducing its undrained shear strength. The volume of water that can be absorbed by the dilating sublayer prior to slope instability is termed the dilation capacity, $V_{\mathrm{dil}}$ . The ratio $V_{\mathrm{con}}∕V_{\mathrm{dil}}$ is a measure of the potential for localization due to strength losses from void redistribution. The localization potential is shown to strongly depend on relative density, slope angle, and thickness of the liquefiable layer. The thickness of the dilating sublayer, a critical parameter, is significantly greater than the thickness of a shear band (which may be only tens of grain diameters). A detailed example is presented to show how the procedure can be applied. The results of the analysis are shown to be consistent with observed deformations and localizations in centrifuge model tests.

The principal focus of this study is the development of a robust macroelement model for soil–pile interaction under cyclic loads. The model incorporates frictional forces and formation of gaps at the soil–pile interface as well as hysteretic behavior of the soil. The plastic envelope of the soil behavior is modeled via the so-called $p$ – $y$ approach, outlined in American Petroleum Institute’s guidelines for design of foundation piles for offshore platforms. The macroelement is an intuitive assembly of various basic elements, each of which incorporating a particular aspect of the soil–pile interaction. The modular structure of this macroelement allows straightforward adaptation of improved constitutive models for its building blocks. Herein, we focus on large-diameter, cast-in-drilled-hole reinforced concrete piles (piers) that are partially or fully embedded in soil. These types of piles are frequently used as support structures in highway construction. Consequently, the numerical robustness of the interaction model is assessed with parametric studies on pile systems and soil types relevant to this type of construction. Both elastic and inelastic pile behaviors are considered in the parametric studies. The results indicate that the proposed interaction element is numerically robust, and thus, amenable to routine structural analysis.

Analytical solutions of normalized maximum deflection and normalized maximum moment for laterally loaded long piles in homogeneous elastoplastic soil under combined loads are presented in this paper. Both the normalized deflection surface and normalized moment surface are continuous and increasing constantly with normalized applied force and moment with various slopes. It shows that the normalized applied force and moment have different contributions to the deflection and moment. In general, the variation of normalized moment surface is relatively moderate compared to normalized maximum deflection. Due to the nonlinear effect, the deflections and moments using superposition approach will be on the unsafe side. The analytical solutions can be used for any elastic materials, any type of soil, and any shapes of pile cross section. Above all, the analytical solutions may be easily applied to calculate the maximum deflection or moment of lateral long piles subject to combined loads accurately using a calculator.

Threshold shear strain for cyclic pore-water pressure, ${\gamma }_t$ , is a fundamental property of fully saturated soils subjected to undrained cyclic loading. At cyclic shear strain amplitude, ${\gamma }_c$ , larger than ${\gamma }_t$ residual cyclic pore-water pressure changes rapidly with the number of cycles, $N$ , while at ${\gamma }_c<{\gamma }_t$ such changes are negligible even at large $N$ . To augment limited experimental data base of ${\gamma }_t$ in cohesive soils, five values of ${\gamma }_t$ for two elastic silts and a clay were determined in five special cyclic Norwegian Geotechnical Institute (NGI)-type direct simple shear (NGI-DSS), constant volume equivalent undrained tests. Threshold ${\gamma }_t$ was also tested on one sand, with the results comparing favorably to published data. The test results confirm that ${\gamma }_t$ in cohesive soils is larger than in cohesionless soils and that it generally increases with the soil’s plasticity index (PI). For the silts and clay having PI=14–30, ${\gamma }_t=0.024–0.06\%$ was obtained. Limited data suggest that ${\gamma }_t$ in plastic silts and clays practically does not depend on the confining stress. The concept of evaluating pore water pressures from the NGI-DSS constant volume test and related state of stresses are discussed.

An extensive program of laboratory tests was carried out to study the effect of reinforcing an earth slope on the lateral behavior of a single vertical pile located near the slope. Layers of geogrid were used to reinforce a sandy slope of 1 $\left(V\right)$ :1.5 $\left(H\right)$ made with sands of three different unit weights representing dense, medium dense, and loose relative densities. Several configurations of geogrid reinforcement with different numbers of layers, vertical spacing, and length were investigated. The experimental program also included studies of the location of pile relative to the slope crest, relative density of sand, and embedment length of pile. The results indicate that stabilizing a soil slope has a significant benefit of improving the lateral load resistance of a vertical pile. The improvement in pile lateral load was found to be strongly dependent on the number of geogrid layers, layer size, and relative density of the sand. It was also found that soil reinforcement is more effective for piles located closer to the slope crest. Based on test results, critical values are discussed and recommended.

The short-term physical response of a 1.5-mm-thick, high-density polyethylene geomembrane with an artificially formed wrinkle and overlying three different subgrade materials (sand and compacted clay at two initial water contents) are reported. The influence of the subgrade, protection layer, backfill, and applied pressure on the fate of the gap beneath the wrinkle, wrinkle deformations, and local geomembrane indentations is investigated. The gap beneath the geomembrane wrinkle was observed to remain with sand above and below the geomembrane, even at applied pressures of $\mathrm{1,100}\mathrm{kPa}$ . The gap was eliminated with compacted clay as the subgrade, depending on the applied pressure and the clay water content. When the clay was compacted at a water content equal to the standard Proctor optimum $\left({\omega }_{\mathrm{opt}}\right)+4\%$ , the gap was eliminated at pressures greater than $100\mathrm{kPa}$ , whereas the gap remained at $250\mathrm{kPa}$ and was eliminated at $500\mathrm{kPa}$ and larger when compacted at ${\omega }_{\mathrm{opt}}+1\%$ . It was found that the presence of a wrinkle increases the maximum geomembrane strain due to local gravel indentations by 10% as compared to a flat geomembrane. The protection layers tested did not significantly influence the change in height and width of the wrinkle, but did influence the local geomembrane strain. The maximum strain in the geomembrane (at $250\mathrm{kPa}$ with $50\mathrm{mm}$ gravel backfill and the softer clay subgrade) was 42% without protection; 15 and 11% with nonwoven needle-punched geotextiles with mass per unit area of 390 and $\mathrm{1,200}\mathrm{g}∕{\mathrm{m}}^2$ , respectively; and 2% with a 150-mm-thick sand protection layer.

The existing design guidelines for buried flexible pipes are limited to depth up to $10\mathrm{m}$ . The increasing use of difficult terrains for infrastructure, landfills, and residential and industrial developments has prompted installation of drainage pipelines under $20–30\mathrm{m}$ high fills. This paper presents the behavior of an instrumented flexible pipe buried under a $47.1\mathrm{m}$ deep fill. For filling above $20\mathrm{m}$ , the measured vertical stress above the pipe exhibited a concave distribution, corresponding to 90 and 110% of the average vertical pressure at the center and edges of the pipe, respectively. The measured results suggest that a triangular lateral pressure distribution can lead to overly conservative and uneconomical results for high fills while Spangler’s analysis is unconservative. Based on the measured results, a revised vertical and lateral earth pressure diagram was proposed for the design of flexible pipe under high fills $>20\mathrm{m}$ . This paper proposes closed-form analyses for estimating the moments and displacements of the pipe subjected to high fill earth pressures. These closed-form solutions agree well with the measured pipe displacements and strains.

Settlement and formation of piping holes on surfaces were observed along a rail embankment subject to normal traffic load. Piezometers were installed in the native peat and soil underneath the embankment inside and outside problematic area to measure the pore pressure responses during train traffic. Peculiar pore pressure responses were observed. Cyclic pore pressures were only measured during the first $60–80\mathrm{s}$ of the $6\text{-}\min$ train passage, and thereafter the pressures decayed rapidly to the initial values. The pore pressure changes in the shallow peat layer were lower than those in the deep soil layer. Possible mechanisms causing such peculiar pore pressure responses, surface settlement, and piping holes were explored and identified. It was found that the stiffness contrast between the stiff, upper granular fill and the soft, native peat material could lead to a redistribution of tensile stress in the granular fill layer to the peat layer due to the moving train load. This stress redistribution promotes the propensity of vertical piping in the peat layer.