Journal of Geotechnical and Geoenvironmental Engineering

An experimental study aimed at improving the understanding of the role of maximum cyclic strain during earthquake loading on the subsequent response of liquefied sands is presented. The behavior of two sands, one generally strain-hardening and the other strain-softening over a range of stress and density states during virgin monotonic loading, is presented to demonstrate that regardless of whether a sand is contractive or dilative in preliquefaction loading, its response following liquefaction is dilative. It is shown that postliquefaction stress-strain behavior can be characterized by four distinct phases. The influence of relative density, confining stress, and the level of maximum shear strain during earthquake loading prior to liquefaction (preliquefaction strain, ${\mathrm{\gamma }}_{\text{preliq}}$) on the response of liquefied sand varies during each of these phases. The first phase of deformation, essentially at zero stiffness, is highly dependent on the level of preliquefaction strain, but is not significantly affected by the density. The final strength of the material in postliquefaction loading (liquefied strength, $S_r$), on the other hand, is highly dependent on the density and loading mode. No clear relationship exists between liquefied strength and preliquefaction strain, but a somewhat weak inverse correlation is noted between strength ratio normalized by initial confining stress and preliquefaction strain. Normalized strength ratio of the liquefied sand varies over a wide range depending on the density and strain history. It varied between $\text{∼}0.04$ and 0.7 in pluviated strain-softening sands, but values as high as two were measured in strain-hardening dense sands. In general, the normalized strength ratio increases with increasing density, but it decreases somewhat with increasing stress level and increasing preliquefaction strain.

Laboratory experiments conducted on corrugated steel, PVC, and high-density polyethylene pipes have demonstrated that deformations in flexible pipes resulting, say, from surface live loads, attenuate rapidly away from the location of load application. As a result, while surface loads in the vicinity of a joint connecting two shallow buried pipe segments influence that joint, the deformations become negligible at the other ends of the two pipe segments. Therefore, solutions for shear, moment, and rotation have been developed assuming that the two pipes are very long, and that the response is not affected by the location or the characteristics of those other joints. This paper presents the formulations of the simplified design equations for flexible pipes, for both moment-transfer and moment-release joints. The design equations are developed using various closed-form solutions for beams on elastic foundations. A parametric study is then presented to examine the factors controlling the structural response of joints in flexible pipes, and comparisons are made to the laboratory experimental measurements.

Large-deformation finite-element analysis has been used to model the undrained response of skirted shallow foundations in uplift and compression. Large-deformation effects involve changes in embedment ratio and operative local soil shear strength with increasing foundation displacement—either in tension or compression. Centrifuge model testing has shown that these changes in geometry affect the mobilized bearing capacity and the kinematic mechanisms governing failure in undrained uplift and compression. Small-strain finite-element analysis cannot by definition capture the effects of changing foundation embedment ratio and variation in local soil strength with foundation displacement. In this paper, load-displacement relationships, ultimate capacities, and kinematic mechanisms governing failure from large-deformation finite-element analyses are compared with centrifuge model test results for circular skirted foundations with a range of embedment between 10 and 50% of the foundation diameter. The results show that the large-deformation finite-element method can replicate the load-displacement response of the foundations over large displacements, pre- and postyield, and also capture differences in the soil deformation patterns in uplift and compression. The findings from this study increase confidence in using advanced numerical methods for determining shallow skirted foundation behavior, particularly for load paths involving uplift.

The results of three full-scale lateral load tests of cast-in-drilled-hole RC piles are evaluated to provide insights into the soil-pile interaction behavior as represented by $p\text{-}y$ curves ($p$ = soil reaction/length; $y$ = lateral pile deflection) spanning from elastic conditions to mobilization of the soil capacity. The test sequence enables evaluation of the diameter effects on the $p\text{-}y$ behavior as a result of testing two otherwise similar specimens, but with different diameters (0.6 and 1.8 m), and evaluation of the head-fixity effects as a result of testing similar specimens (with a 0.6 m diameter) under flagpole and fixed-head conditions. A constrained exhaustive search procedure that facilitates data interpretation even in the presence of severe shaft nonlinearity is introduced, which was needed because the testing was performed to full structural failure conditions. The $p\text{-}y$ curves obtained with the present test data differ from the predictions of a standard (American Petroleum Institute) model, indicating stronger soil reactions for the fixed-head and 1.8-m-diameter flagpole specimens and weaker and softer backbone curves for the 0.6-m-diameter flagpole test.

Equivalent number of cycles ($N_{\text{cyc}}$) is a significant factor in assessing liquefaction potential during earthquakes. However, the effects of $N_{\text{cyc}}$ are considered a deterministic value by using a magnitude scaling factor, and the uncertainties of these effects have not been included in the current design practice. This paper calculates $N_{\text{cyc}}$ within the soil mass by deconvolution analysis as a function of the period of soil layer from the ground surface ($T_s$) and the soil property ($b$) using a wide range of acceleration time histories. The predictive model of $N_{\text{cyc}}$ is developed as variable dependent on earthquake magnitude, peak ground acceleration (PGA), and ratio of spectral acceleration, $T_s$ and $b$. Then, the $N_{\text{cyc}}$ model is combined with the ground-motion prediction equation of PGA and the prediction equation of seismic shear-stress reduction coefficient ($r_d$) to obtain the prediction equation of the seismic demand of the liquefaction potential ($K_{1\text{cyc}}$). The standard deviation of $K_{1\text{cyc}}$ is also modeled on the basis of the aleatory variability of PGA, $r_d$, and $N_{\text{cyc}}$ with correlations between these residuals. This predictive model of $K_{1\text{cyc}}$ is implemented in probabilistic seismic hazard analysis (PSHA) to show the impact of these uncertainties on design practice.

Internal fluidization, the process whereby granular soil is transformed into a fluid-like state when liquid or gas is pumped into it, is of importance in a number of civil and geotechnical engineering processes, for example, pipe leakage, flow through sheet piling, pile jetting, and spudcan extraction. This paper draws together the limited literature on the subject and identifies the stages in the process by which fluidization occurs. Using data from small-scale experiments and simple analysis, factors affecting the onset of fluidization and its development are identified.

Bentonite was modified to prevent alterations in hydraulic conductivity when permeated with aggressive inorganic solutions. Acrylic acid within bentonite slurry was polymerized to create a bentonite-polymer composite (BPC). Tests indicate that BPC generally swells more and retains low hydraulic conductivity compared with natural sodium bentonite (Na-bentonite) when contacted with aggressive inorganic solutions. BPC in deionized water swelled greater than 3.8 times the swell of the Na-bentonite used to create BPC (73 versus $19\hspace{0.17em}\text{mL}/2\hspace{0.17em}\mathrm{g}$). In 500 mM ${\text{CaCl}}_2$, however, swell of BPC was similar to swell of calcium bentonite ($\text{<}10\hspace{0.17em}\text{mL}/2\hspace{0.17em}\mathrm{g}$). Thin layers of BPC simulating geosynthetic clay liners were permeated directly with 5–500 mM calcium chloride (${\text{CaCl}}_2$) solutions and extreme pH solutions (1 M NaOH with pH 13.1, 1 M $\text{HN}{\mathrm{O}}_3$ with pH 0.3). BPC maintained low hydraulic conductivity ($\text{<}8\times {10}^{-11}\hspace{0.17em}\text{m/s}$) for all solutions for the duration of testing ($\text{>}2\hspace{0.17em}\text{years}$). In contrast, Na-bentonite and superabsorbent polymer (similar to the polymer in BPC) permeated with the same solutions had hydraulic conductivities at least three orders of magnitude higher (except for 5 mM ${\text{CaCl}}_2$). Hydraulic conductivity of BPC does not follow the classical hydraulic conductivity-swell relationship typical of Na-bentonite. BPC eluted polymer during permeation but maintained low hydraulic conductivity. Polymer elution was lower in more concentrated ${\text{CaCl}}_2$ solutions.

Installation of a displacement pile often involves complex loading modes that cause substantial changes in the state of the soil surrounding the pile. When a displacement pile is installed in saturated clay, significant excess pore pressure develops. As the excess pore pressure dissipates over time, the effective stresses in the soil surrounding the pile and the pile capacity increase. This paper investigates jacking of piles into clay using finite-element analysis. A two-surface plasticity-based constitutive model for clays was implemented in the finite-element code Solid Nonlinear Analysis Code. Based on the numerical results, equations are developed for quantifying the effects of undrained and residual shear strength on the shaft resistance of jacked piles in clay. The gain in shaft resistance over time is assessed and setup factors are proposed that can be used to estimate the gain in shaft resistance as a function of time after installation of a jacked pile in clay. Good agreement was obtained between the shaft resistance values calculated with the proposed equations and the data available in the literature.

Establishing the stress conditions developed around displacement piles in sands is crucial to improving the understanding and modeling of their behavior. High-quality experiments and theoretical analyses are providing new insights into the effects of penetration on stress conditions. This paper synthesizes the findings from three independent experimental studies on normally consolidated silica sands and a trio of numerical analyses that tackle the problem from different perspectives. The significant degrees of uncertainty in the measurements and predictions are recognized and significant differences between data sets are discussed and largely resolved. Applying a consistent normalized interpretive framework leads to clear common trends regarding how installation affects the stress regime. While the main emphasis is placed on the radial effective stresses developed around pile shafts, the circumferential and vertical stress states are also considered.

The potential for chemical incompatibility between soil-bentonite (SB) backfills of vertical cutoff walls composed of conventional (chemically unmodified) sodium bentonite (CSB) and contaminated groundwater has led to evaluation of chemically modified bentonites for improved chemical resistance. Accordingly, the hydraulic conductivity to tap water ($k_w$) and to ${\text{CaCl}}_2$ solutions ($k_c$) of SB backfills amended with a polymerized bentonite known as bentonite polymer nanocomposite (BPN) were measured and compared with those for a traditional backfill composed of CSB. The BPN was used both as a dry amendment and as the constituent in the bentonite slurry. Three backfills were evaluated, viz, clean silica sand amended with either 2 or 5% dry BPN and mixed with 2% BPN slurry (i.e., 2BPN2 and 5BPN2, respectively), and the same sand amended with 5% dry CSB and mixed with 5% CSB slurry (5CSB5). Based on permeation with 50 mM ${\text{CaCl}}_2$, the ratio $k_c/k_w$ varied in the order of $2\text{BPN}2<5\text{CSB}5<5\text{BPN}2$, such that the 5BPN2 backfill performed the worst in terms of chemical resistance. However, because $k_w$ for the 5BPN2 backfill ranged from approximately two to four orders of magnitude lower than that of the other backfills, the final $k_c$ for the 5BPN2 backfill of $3.2\times {10}^{-11}\hspace{0.17em}\text{m/s}$ was the lowest among the three backfills and was almost two orders of magnitude lower than that for the 5CSB5 backfill of $2.5\times {10}^{-9}\hspace{0.17em}\text{m/s}$, despite an overall lower total bentonite content for the 5BPN2 backfill (i.e., 5.5 versus 7.1%). Thus, for the permeant liquids and materials used in this study, the overall hydraulic performance of the backfill containing 5% dry BPN was significantly better than that of the backfill containing 5% dry CSB.

Traditional (unmodified) sodium bentonite (Na-bentonite) has been shown to exhibit semipermeable membrane behavior, which is beneficial in terms of the use of Na-bentonites as barriers or components of barriers for hydraulic containment applications. However, degradation of such membrane behavior due to the diffusion of cations into the bentonite also is known to occur, and this degradation increases with increasing salt concentration and increasing valence (charge) of the principle salt cation (e.g., ${\text{Ca}}^{2+}$ versus ${\mathrm{K}}^{+}$). In this study, the membrane behavior of a polymerized bentonite referred to as a bentonite-polymer nanocomposite (BPN) was determined during multistage membrane tests using solutions of ${\text{CaCl}}_2$. The BPN illustrated improved membrane behavior relative to that previously reported for both traditional and other chemically modified bentonites. However, complete degradation of the membrane behavior was ultimately observed for specimens of the BPN exposed to $10\hspace{0.17em}\text{mM}\hspace{0.17em}{\text{CaCl}}_2$ for a test conducted in a rigid-wall cell and $20\hspace{0.17em}\text{mM}\hspace{0.17em}{\text{CaCl}}_2$ for a test conducted in a flexible-wall cell. The destruction of membrane behavior for the specimen in the rigid-wall cell was attributed to short-circuiting along the side walls of the rigid-wall cell after shrinkage of the BPN, whereas destruction of the membrane behavior in the flexible-wall cell correlated with the time required to reach steady-state diffusion of calcium (${\text{Ca}}^{2+}$). Thus, the enhanced calcium-resistant behavior of the BPN was limited and was affected by the type of cell (rigid-wall versus flexible-wall) in which the membrane behavior was measured.

The shear-wave velocity and associated small-strain shear modulus of municipal solid waste (MSW) are important engineering parameters in evaluating the seismic response of MSW landfills as well as in characterizing the waste material and its response to static loads. Semiempirical and empirical models for the shear-wave velocity are presented. The semiempirical model is a more comprehensive model that aims to separately capture the effect of waste density and confining stress on the shear-wave velocity of MSW. It is based on similar models for soils, and its mathematical expression is formulated using data generated from large-scale laboratory studies on reconstituted MSW. The empirical model has a simpler mathematical expression that is a function of depth only. The parameters of both models are derived by calibrating them against a total of 49 in situ shear-wave velocity profiles at 19 MSW landfills, i.e., 13 profiles from four landfills in Michigan generated as part of this study and 36 additional shear-wave velocity profiles from 15 landfills available in the literature. The models can be used to estimate the shear-wave velocity of MSW and to evaluate the seismic response of landfills. Also, in the absence of in situ data, the models can be used at existing MSW landfills for preliminary design purposes. The models are not intended to replace in situ data and do not predict abrupt changes in the shear-wave velocity profile as a result of abrupt changes in waste type and composition.

In the aftermath of Hurricane Katrina, studies pointed out that gap formation was related to breaches of many floodwalls in New Orleans. However, it is still necessary to discern whether those gaps were the cause or the result of the failure to justify the application of retrofitting techniques designed to correct gap formation problems. For that purpose, this study conducted numerical and analytical evaluations to investigate the in-depth mechanism of gap formation using an effective stress approach. To this end, it was found that gap was the cause of failure for the London Ave. canal because of the seepage effect; however, it could be the result of failure for the 17th St. canal because of the subsidence of the soft soil layer underneath the levee. When the stiffness and strength of the soft layer were increased considering the geotechnical variability in the numerical analysis for the 17th St. canal, however, it showed that the failure mode changed and gap became the cause of failure, meaning that the question of whether gap is the cause or the result of failure depends on the subtle difference in geotechnical conditions. This result also implied that the gap formation as a possible cause of failure must be considered in planning the retrofitting techniques even for the area where gap was not the immediate cause of the failure.

This study aims to address how efforts spent in geotechnical site investigation can be linked in an objective and defensible way to the final design dimensions of a geotechnical structure. A previously developed pad foundation example is adopted for illustration. Three aspects of geotechnical information are addressed: a variety of in situ and laboratory tests, precision of the tests, and local experiences in the estimation of soil properties that permit reduction of transformation uncertainties between test indexes and design parameters. Four simplified reliability-based design methods based on partial factors and quantiles are calibrated for the pad foundation. Their performances in linking site investigation efforts to final design savings are studied. Among these methods, the quantile methods are found to be the most responsive to the availability of geotechnical information, whether in the form of site investigation efforts or local experiences. The quantile methods can fill a critical gap in current design practice, that is, to monetize the value of geotechnical information in the form of an increase/reduction of construction costs associated with changes in design dimensions in an objective and defensible way that can be communicated to nonengineers.

This paper describes a new formulation of the material point method (MPM) for solving coupled hydromechanical problems of fluid-saturated soil subjected to large deformation. A soil–pore fluid coupled MPM algorithm based on Biot’s mixture theory is proposed for solving hydromechanical interaction problems that include changes in water table location with time. The accuracy of the proposed method is examined by comparing the results of the simulation of a one-dimensional consolidation test with the corresponding analytical solution. A sensitivity analysis of the MPM parameters used in the proposed method is carried out for examining the effect of the number of particles per mesh and mesh size on solution accuracy. For demonstrating the capability of the proposed method, a physical model experiment of a large-scale levee failure by seepage is simulated. The behavior of the levee model with time-dependent changes in water table matches well to the experimental observations. The mechanisms of seepage-induced failure are discussed by examining the pore-water pressures, as well as the effective stresses computed from the simulations.

Discrete columns, such as stone and soil-cement columns, are often used to improve the liquefaction resistance of loose sandy ground potentially subjected to strong shaking. The shear stress reduction in the loose ground resulting from the reinforcing effect of these stiffer discrete columns is often considered as a contributing mechanism for liquefaction mitigation. Current design practice often assumes that discrete columns and soil deform equally in pure shear (i.e., shear strain–compatible deformation). In addition, because the discrete column is stiffer than the soil, it is assumed to attract higher shear stress, thereby reducing the shear stress in the surrounding soil. In this paper, shear stress reduction in liquefiable soils and shear strain distribution between liquefiable soil and discrete columns along with the potential of development of tensile cracks is investigated using three-dimensional linear elastic, finite-element analysis. Parametric analyses are performed for a range of geometries, relative stiffness ratios, and dynamic loadings. These linear elastic results provide a baseline against which future nonlinear modeling results can be compared, but they are also sufficient for demonstrating that shear stress reductions are far less than predicted by the assumption of shear strain compatibility. These numerical results are consistent with those of other researchers and further call into question the appropriateness of the strain-compatibility assumption for design.

Current design methods for piles in liquefied ground assume that the ultimate soil pressures acting on the pile are drastically reduced relative to the reference values in the absence of liquefaction. However, there is controversy about the adopted design parameters and their effects. Furthermore, it has been experimentally shown that soil pressures are not always reduced, but they may increase well above the recommended design values because of flow-induced dilation of the liquefied soil around the upper part of the pile. In view of this, the pile response is simulated in this paper using a three-dimensional, fully coupled dynamic elastoplastic numerical analysis. The methodology is first verified against results from centrifuge experiments and consequently applied parametrically for various pile, soil, and seismic excitation characteristics. It is thus shown that dilation-induced negative excess pore pressures are indeed possible for common pile and soil conditions at the upper segments of the pile, having an overall detrimental effect on pile response. It is further found that, apart from the commonly considered effect of relative sand density, ultimate soil pressures are affected by a number of other dilation-related parameters, such as the effective confining stress, the permeability of the sand, and the predominant excitation period as well as the pile diameter and bending stiffness. To quantify the relevant effects, new multivariable relationships are established and subsequently evaluated against the empirical methodologies that are currently used in practice.

Approximately 240 resonant column (RC) tests have been performed on 26 clean quartz sands with piecewise linear, gap-graded, S-shaped, and other smoothly shaped grain-size distribution curves. For each material, the small-strain shear modulus, $G_{\text{max}}$, the shear modulus degradation curves, $G\left(\gamma \right)/G_{\max }$, and the damping ratio curves, $D\left(\gamma \right)$, were measured at different pressures and densities. The applicability of the extended empirical equations proposed by the authors in two previous publications, considering the influence of the uniformity coefficient, $C_u=d_{60}/d_{10}$, of the grain-size distribution curve, has been inspected for the various tested materials. These equations were developed originally based on RC test data for linear gradations. It is demonstrated that the extended empirical equations work well also for most of the more complicated grain-size distribution curves tested in the current study.

This study develops assessment formulas for the displacement ductility capacity of a fixed-head pile in cohesionless soils. The derivations of the formulas are based on an ideal model of a semiinfinite nonlinear pile in a Gibson soil, whose subgrade reaction modulus increases linearly with depth, to link the displacement ductility capacity of the pile with the pile–soil system parameters. The parameters in the formulas include the sectional overstrength ratio and curvature ductility capacity, as well as a modification factor for considering soil nonlinearity. The modification factor is a function of the displacement ratio of the pile’s ultimate displacement to the effective soil yield displacement, which is constructed through a number of numerical pushover analyses. The format of the formulas is similar to that for a pile in cohesive soils. For the case of linear soil, the formulas provide a lower-bound estimate of pile ductility capacity; the displacement ductility capacity of a pile in cohesionless soils is larger than that in cohesive soils. For the case of nonlinear soil, the modification factor for soil nonlinearity in cohesionless soils (the American Petroleum Institute sand $p\text{-}y$ model) is smaller than in cohesive soils (the Matlock clay $p\text{-}y$ model).

Continuous compaction control (CCC) with constant roller settings provides useful data on the stiffness of the layers involved. By carefully analyzing the data, it is possible to estimate how compaction will evolve during the construction process. Applying geostatistics to CCC data means that spatial variability can be quantified, something that is difficult using simple statistical analysis. Univariate statistics of CCC measurements alone do not describe spatial variability, and neither do they address the issue of uniformity from a spatial standpoint. Furthermore, it is important to choose the variogram model wisely, so that the factors distinguishing the areas being investigated can be fully appreciated. This article was prepared using statistics and geostatistics on experimental data obtained from an embankment made of recycled materials.