Journal of Geotechnical and Geoenvironmental Engineering

Time-dependent response of piled raft foundations (PRFs) in saturated, normally consolidated and moderately overconsolidated clayey soils under the single-drainage condition is investigated using three-dimensional, elastoplastic finite-element (FE) analysis with the modified cam clay (MCC) soil constitutive model. Four different types of clay (Boston Blue Clay, San Francisco Bay Mud, London Clay, and Shanghai Clay) with different values of overconsolidation ratio (OCR) ($\mathrm{OCR}=1$, 2, and 5) and 20 different configurations of rectangular PRFs are considered for the study. The settlement response and load sharing of PRFs are investigated. Regression analyses are performed with the FE analysis results to obtain fitted equations for immediate settlement, primary consolidation settlement, and degree of consolidation of PRFs. These equations are applicable to PRFs with cast in situ bored piles similar in size to those considered in this study. The proposed equations can be used to estimate time-dependent PRF settlement in normally consolidated and moderately overconsolidated clay as part of preliminary design calculations.

This study proposes a new method to introduce the cementation effect into existing elastoplastic constitutive models for soils. The mechanical properties of cement-treated soil are evaluated via element tests and compared with those of naturally deposited clay. The similarities and differences between cement-treated soils and naturally deposited clays are studied, focusing on two states, the undisturbed and remolded states. The effective stress for cement-treated soils incorporating an internal state variable representing the cementation effect is newly defined to describe the mechanical properties of cement-treated soils. Moreover, by applying this extended effective stress to the super-subloading yield surface (SYS) Cam-clay model, which is an elastoplastic model for soils based on the skeleton structure concept, the scope of this constitutive model is extended to include cement-treated soils. The cementation effect introduced by the proposed method allows reproducing the mechanical behavior of the cement-treated soil. Finally, a brittle behavior not described at the element level can be obtained, leading to a soil–water coupled finite deformation analysis incorporating the proposed constitutive model.

Numerous studies have been conducted to evaluate the influence of internal erosion on the geotechnical properties of soil under unidirectional seepage. Yet cyclic gradients prevail in natural or engineering systems, and the mechanical consequences of soil subjected to cyclic hydraulic gradient reversal have not been addressed in the literature. This paper reported the first batch of internal erosion tests on a modified stress-controlled triaxial apparatus that allows alteration of seepage direction and hydraulic gradient reversals. Three different schemes of hydraulic gradient application, namely monotonic stepwise loading, cyclic reversal after monotonic loading, and direct cyclic loading, were adopted. In each test, the cumulative particle loss, deformation, hydraulic conductivity, and posterosion shearing behavior were evaluated. It was found that the cyclically reversed hydraulic gradient resulted in more severe erosion at the same level of mean hydraulic gradient. Microscopic analysis was also conducted to investigate the mechanism of internal erosion under cyclic hydraulic gradient reversal, in which mitigation of clogging within the soil matrix was observed and found to facilitate the progression of internal erosion.

In laboratory testing, the liquefaction resistance of sands is typically evaluated using cyclic triaxial and simple shear tests. These tests cannot be used in a rigorous manner to systematically assess the effects of principal stress rotation and intermediate principal stress changes on the undrained cyclic response of sands. In this study, the effect of these two factors on the liquefaction resistance of Ottawa sand was investigated using a cyclic hollow cylinder apparatus. At similar initial states of fabric and mean effective stress following $K_0$ consolidation, the liquefaction resistance of Ottawa sand deposited underwater can (1) decrease by 50%–80% as the major principal stress direction moves away from the vertical with ${\sigma }_2^{\prime }={\sigma }_3^{\prime }$, or (2) increase by 200% to 380% as ${\sigma }_2^{\prime }$ increases while ${\sigma }_1^{\prime }$ remains vertical depending on the liquefaction criterion (strain levels). When the stress state defined by the imposed boundary condition deviated from axisymmetric compression, the combined effect on the liquefaction resistance was governed by principal stress rotation.

An entire large-scale retaining structure can be monitored by simulating a three-dimensional point cloud obtained by laser scanning. The behavior of a retaining structure composed of sheet piles according to excavation was analyzed by the displacement mapping method in this paper. The displacement errors can be generated due to inclined sections, U-shaped protrusions of sheet piles and cutting point clouds, and the fall and deposition of soil adhering to the sheet pile. Therefore, the analysis error was minimized by pretreatment of the point cloud considering the shape of the sheet pile before displacement mapping. For displacement mapping, the cloud to mesh (C2M) distance was calculated by segmenting the point cloud of the retaining structure into 5 rows and 20 columns, which have about 100 elements. Analysis of seven monitoring results from Day 0 to Day 35 was performed, and the maximum displacement occurrence point and the expansion of displacement with time were evaluated by displacement mapping. In an in-depth analysis after displacement mapping, it was possible to estimate the displacement variation in the vertical direction of a pile in which the excessive displacement occurred as well as the change pattern of the displacement in the horizontal direction of the entire pile head. A crack found at the top of a sheet pile occurred due to excessive displacement, which was verified by visual inspection.

In this paper, we present a probabilistic predictive procedure for a foundation’s permanent average settlement on liquefiable soils improved with ground densification. The proposed procedure is based on 770 three-dimensional (3D), fully coupled, effective-stress, finite-element analyses designed through quasi-Monte Carlo sampling of key input parameters. The numerical models are themselves calibrated and validated with centrifuge model studies, and they consider realistic, nonlinear, 3D structures on shallow foundations, seismic soil–structure interaction, interlayering and layer cross interactions, ground densification properties and geometry, and ground motion characteristics. We use nonlinear regression with lasso-type regularization to estimate model coefficients. The primary predictors of a foundation’s settlement are identified as the cumulative absolute velocity of the outcropping rock motion; total thickness of the soil deposit above bedrock and cumulative thickness of the critical liquefiable layer(s); the foundation’s bearing pressure, size, and embedment depth; the structure’s total height; the achieved density and size of ground improvement; and the thickness of the remaining undensified susceptible soils within the foundation’s influence zone. In the end, the predictive model is shown to capture the trends in a limited number of centrifuge and field case histories collected from the literature. The insight from the numerical database and the first-of-its-kind predictive model aims to guide the design of liquefaction mitigation strategies that improve the performance of the soil–foundation–structure system holistically and reliably.

One of the major risks to civil structures during an earthquake is the occurrence of liquefaction in loose saturated sand deposits. The main consequences of liquefaction include lateral spreading deformations and postliqufaction reconsolidation settlement. In situ tests, such as standard penetration tests (SPTs), commonly are used in one-dimensional models for estimating liquefaction-induced deformation, which provide ground deformation only at limited locations at which SPTs are performed. However, magnitudes of liquefaction-induced ground deformation within a specific site may exhibit significant spatial variation when subsurface soils are not homogeneous or when they vary spatially within a site. Therefore, using the ground deformations estimated from limited SPT locations to represent a whole site might provide misleading results and cannot properly predict the differential ground settlement or displacement, posing a significant risk to civil structures. To deal with this challenge, a novel approach was developed in this study for characterizing spatial variation of the soil lateral spreading displacement and reconsolidation settlement in a cross section of a specific site from limited SPTs with consideration of soil spatial variability along both depth and the horizontal direction. The proposed method was illustrated using both simulated data and real data.

A significant amount of seismic site response research over the past decade has focused on our abilities to replicate recorded ground motions at borehole array sites, where both the input (rock) and output (surface) ground motions are known. When viewed in aggregate, these studies have found that approximately 50% of borehole array sites are poorly modeled using one-dimensional (1D) ground response analyses (GRAs) based on a single shear wave velocity ($Vs$) profile, with individual studies reporting values between approximately 30%–80%. While there is no doubt that some sites are indeed too variable to be modeled using 1D GRAs, it is possible that simple 1D analyses could still be effectively used at many sites if spatial variability is accounted for via a rational, site-specific approach. In this study, we investigate five alternative approaches that can be used to account for spatial variability in 1D GRAs: (1) $Vs$ randomization, (2) shear wave travel time randomization, (3) utilization of $Vs$ suites derived from surface wave testing covering a large area, (4) incorporation of a pseudo-3D $Vs$ model derived from a horizontal-to-vertical spectral ratio geostatistical approach, and (5) damping modifications. These approaches are investigated at two US borehole array sites (the Treasure Island and Delaney Park Downhole Arrays) so that the GRA results can be compared with recorded small-strain ground motions. Spatial variability is accounted for by generating approximately 250 $Vs$ profiles for each approach, except for damping modifications, wherein only a single $Vs$ profile is used, but with increased damping to account for wave scattering originating from spatial discontinuities. Through qualitative and quantitative comparisons, we assess the relative and absolute effectiveness of each approach, highlight their limitations, and propose potential improvements that can help overcome these limitations in practice.

Static liquefaction of mine tailings has been the interest of many studies as these materials are generally deposited in a loose condition and stored at high saturation ratios. Yet few researchers have investigated the behavior of mine tailings in stress paths involving extensional consolidation or shearing in extension. In this study, the results of a set of experiments aimed at investigating the static liquefaction behavior of saturated loose gold mine tailings samples in triaxial compression and extension shear tests are described. Monotonic tests are carried out on isotropically and $K_0$-consolidated samples to assess the effect of stress-induced anisotropy and mode of shearing on the instability and critical state behaviors of tailings. The comparison of undrained extension and compression shearing behaviors of samples consolidated to similar densities and stress conditions show a profound difference in their undrained shearing responses. This is attributed to the angular shapes of tailings particles that amplify the effects of particle orientation and sample fabric, as well as microstructural changes induced by different loading paths. Postliquefaction and yielding undrained shear strengths and effective friction angles from different modes of consolidation and shearing are examined. In both undrained compression and extension tests, tailings samples exhibit a limited liquefaction behavior after yielding, followed by a strain-hardening (dilative) behavior. Differences in tailings behavior under different loading directions and anisotropic stresses indicate the importance of considering the effects of these phenomena on the stability analysis of mine tailings dams.

This study develops a novel method for reconstructing three dimensional (3D) granular grains from computed tomography (CT) images. Unlike previous studies requiring trial-and-error hyperparameters, the hybrid algorithm introduced here, integrating the random forest (RF) algorithm and enhanced by particle swarm optimization for automatic determination of hyperparameters, is the first to train the model for constituent classification and grain segmentation. In addition, and different from previous manual methods, a convolution kernel is applied to assign an initial level set function inside an individual grain and determine whether to activate the level function for automatically reconstructing 3D grains from a CT image. All results indicate the hybrid algorithm can rapidly search the optimum hyperparameters, providing a more effective way to identify the optimum RF-based model. This model segments grains with an accuracy of 90%, in comparison with a 52% accuracy achieved by the conventional watershed algorithm. The convolution kernel can accurately and automatically identify individual grains, avoiding manual assignment of an initial calculation area and ensuring grains are correctly reconstructed. Overall, the proposed method provides a more intelligent and effective way to reconstruct 3D grains from CT images.

This paper experimentally investigates the mechanical properties of foam-injected gravel by means of uniaxial compression tests and uniaxial creep tests. Bonding of noncohesive soils by foam injection is a novel soil improvement method that can be applied for the stabilization of cohesionless soils at the tunnel face and behind soldier pile walls. Limited data on the mechanical behavior of foam-injected soils is available in the literature. A method for the preparation of homogeneous and reproducible test specimens was developed. The testing program included the variation of the factors that influence the mechanical behavior (e.g., initial soil density, grain size, strain rate, curing time, and stress level). Similar to cemented soils, the foam-injected soils show an elastoplastic stress–strain response and softening beyond the peak. The mechanical behavior is time-, stress- and rate dependent. The strength and stiffness can be described by the porosity–binder concept considering the influence of strain rate, soil density, and foam content.

This study presents a reliability-based analysis performed using a coupled thermo-hydro-bio-mechanical model to assess the long-term performance of a typical landfill cell geometry under simulated bioreactor landfill conditions. Several Monte-Carlo simulations were carried out by considering randomly generated lognormally distributed fields of different properties of waste to represent the waste heterogeneity. The long-term performance of the simulated bioreactor landfill cell was evaluated in terms of wetted area ($W_A$), cumulative methane (${\mathrm{CH}}_4$) gas generated ($W_{{\mathrm{CH}}_4}$), maximum surface settlement ($S{S}_{\max }$), and maximum temperature of the waste ($T_{\max }$), at different intervals of time during the operation of the simulated bioreactor landfill cell. A deterministic analysis was also conducted using the mean values for the different properties of waste. The results show that the deterministic analysis overpredicts the maximum value for $W_A$, $W_{{\mathrm{CH}}_4}$, $S{S}_{\max }$, and $T_{\max }$ obtained from the stochastic analysis by approximately 10%, 17%, 25%, and 14%, respectively. The most likely values estimated for the four performance metrics from the stochastic analysis were approximately 44%, $\mathrm{88,000}{\mathrm{m}}^3$, 5.5 m, and 62.5°C, respectively. It was also determined that the waste’s anisotropy with regard to its hydraulic conductivity and the biodegradation-induced void change parameter had the most influence on $W_A$ and the $S{S}_{\max }$ in the landfill cell, respectively.

Permeable reactive barriers (PRBs) are an environmentally friendly and cost-effective in situ remediation technology that have been used to restore polycyclic aromatic hydrocarbon (PAH)-contaminated groundwater. However, the understanding of removal mechanisms of the pollutant from groundwater remains a challenge due to the complex interactions between microbial evolution, organic carbon kinetics, and multiple chemical reactions. In this study, a one-dimensional reactive transport model was developed to study 450-day column experiments for removal of phenanthrene from groundwater using new PRB materials A (including wheat straw) and B (including coconut shell biochar). The modeling results provided a deeper understanding of the removal process for phenanthrene, and showed that Material B had a higher removal efficiency than Material A over 34 days. The removal efficiency of phenanthrene in both Materials A and B was close to 100% in the PRB system. This was because (1) Material B had a higher adsorption capacity for phenanthrene than Material A, and adsorption played an important role in the short term (e.g., 20 days), whereas biodegradation controlled longer-term removal processes; (2) the biomass in Column B was higher ($p<0.05$) than that in Column A; and (3) Column B had a higher microbial yield coefficient that could favor longer-term microbial growth and biodegradation activity. Material B might have greater potential than Material A for longer-term remediation performance. The simulated results generally were in agreement with the experimental results and support the development of field-scale pilot testing of these materials for groundwater remediation.

Schmertmann’s method is one of the traditional methods for estimating the settlement of axially loaded footings in sand using cone penetration test (CPT) data. The method was developed for footings on a single, uniform sand layer; it assumes a depth of influence below the footing base within which most of the soil deformations take place and an influence diagram to quantify the influence factor as a function of depth. However, the literature contains limited information on the strain influence diagrams for footings on layered sands, and, as a result, there is no way to accurately account for the effect of sand layering on footing settlement. In this paper, Schmertmann’s approach for calculating the strain influence factor is modified to account for the effect of two sand layers with varying thickness and relative density. Penetration experiments were performed using a half-square model footing (width $B=90\mathrm{mm}$) placed on the surface of both single and two-layered (dense over medium-dense and medium-dense over dense), air-pluviated silica sand samples prepared inside a half-cylindrical calibration chamber designed for digital image correlation (DIC) analysis. The test results indicate that both the thickness and relative density of the top sand layer (the layer in contact with the footing base) affect the parameters of the strain influence diagram. For dense sand over medium-dense sand, the depth to the peak strain influence factor varies with the thickness of the dense layer; however, when the thickness of the dense layer is $1.5B$ or greater, the strain influence diagram is similar to that obtained for a single, uniform sand layer. In contrast, for medium-dense sand over dense sand, the peak value of the strain influence factor varies with the thickness of the medium-dense layer up to a value of $1B$. Based on the results obtained in this study, new strain influence diagrams are proposed for settlement calculation of square footings on two-layered sand profiles. The proposed method for estimation of footing settlement in layered sand is validated against measured data obtained from a full-scale, instrumented footing load test reported in the literature.

Yard loads may induce slope deformation and compress the piles of pile-supported wharfs, resulting in structural damage. In this paper, centrifuge tests were conducted to investigate yard load induced performances of pile-supported wharfs reinforced with T-shaped and F-shaped soil cement mixing (TSCM and FSCM, respectively) retaining walls. The TSCM and FSCM walls were located in the bent-yard connecting section and wharf performances were presented in terms of soil movements, bent displacements, soil and pore pressures, and pile bending moments. The results show that the slope soil migrated toward the waterside as the soil cement mixing (SCM) walls tilted, inducing tilting failure of the pile-supported wharf. The FSCM wall–reinforced bent showed greater displacements than the TSCM wall–reinforced bent at the same load intensities. Pore pressures were registered immediately after yard loads were applied but dropped to constant values or kept decreasing over time during the unloading period. Soil pressures generally increased with yard loading in the upper part but exhibited increasing-decreasing tendencies in the lower part. The soil pressures on the FSCM side were generally greater than those on the TSCM side in the upper and middle parts but smaller in the lower part. The bending moments on the FSCM side were generally larger than those on the TSCM side on landside because the structure-soil interaction was more intense. SCM walls are feasible and beneficial for reinforcing pile-supported wharfs under yard loads, and TSCM walls seem to be superior to FSCM walls considering their improved performance and economic efficiency.

This paper explores the influence of building cover and pile toe boundary conditions on ground temperature distributions surrounding energy piles. Experimental and numerical studies were conducted on two isolated cast-in-place energy piles installed in dense unsaturated sand, one exposed to the atmosphere at the ground surface ($\text{diameter}=0.6\mathrm{m}$ and $\text{length}=16.1\mathrm{m}$) and the other installed under a six-story building ($\text{diameter}=0.6\mathrm{m}$ and $\mathrm{length}=10\mathrm{m}$). Investigations were conducted for monotonic heating and daily cyclic temperature changes of the piles ranging between 10°C and 35°C. The changes in ground temperature decreased as radial distance increased from the edge of both piles. Cyclic temperatures in both piles induced lower ground temperature changes and decreased the radial thermal influence zone compared with monotonic heating. However, the radial thermal zone in cyclic operating mode can be influenced by different ratios of heating to cooling times and hence should be selected carefully to avoid unexpected ground temperature changes. Atmospheric effects were observed up to a depth of 2 m for the energy pile exposed to the atmosphere. The insulation provided by the building footprint slightly decreased the impacts of ground-atmosphere interaction on the soil temperature distribution with depth near the surface compared to the energy pile exposed to the atmosphere. The ground temperature variations were dominant along the length of the heat exchanger loops for both piles. However, they were negligible near the pile toe below the heat exchanger loops for both piles.

Removal of soil around a bridge foundation due to scour results in a reduction of the lateral and vertical foundation capacity due to the loss of soil support. The common approach in modeling the scour phenomenon of removal of soil springs without modifying the parameters of the remaining soil fails to consider the change of stress state of the remaining soil and the formation of scour hole geometry around the pile foundation. In practice, both of these factors impact the mechanical properties of the remaining soil and the resulting expected structural response of the pile under loadings. This paper proposed a methodology to comprehensively evaluate the combined effects of stress history and scour hole dimensions on piles under scour conditions in uniform soil. It enabled the examination of the lateral and axial behaviors of a loaded pile subject to scour and is applicable for both cohesive and cohesionless soils. The methodology was validated with results from field tests for no-scour scenarios and verified with existing numerical models for scour scenarios. Quantification of the soil effects was investigated through lateral pile deflection and load-settlement curves for lateral and axial behaviors, respectively. Load-settlement curves demonstrated that including the effect of stress history results in increases of up to 34.1% and 61.1% in estimated pile settlement for sand and clay, respectively, leading to potential unconservative designs if soil effects are not properly included in the analysis.

This paper presents the results from a prediction event, organized by the University of Western Australia (UWA) and the National Geotechnical Centrifuge Facility (NGCF), and performed as part of the International Symposium on Frontiers in Offshore Geotechnics to assess uncertainty in predicting the monotonic and cyclic lateral response of conductors. Geotechnical professionals from around the world were invited to predict the response of a model conductor (a flexible pile) subjected to a series of loading sequences in a centrifuge. A normally consolidated fine-grained soil was used in the tests, which was characterized by soil elements and in-flight T-bar penetrometer testing. While some participants provided accurate predictions, the mean response was an overestimate of the monotonic and cyclic load at the pile head, which was significant for large and very small displacements. An analysis of the submissions is presented to quantify the variability of the predictions received, assess the consequences of each design, and relay the uncertainty associated with engineering judgment in design.

A significant pressing issue in microbially induced calcium carbonate precipitation (MICP) is the characterization of the heterogeneous growth mechanics of calcium carbonate (${\mathrm{CaCO}}_3$) crystals. This study aimed to visualize the bacteria and ${\mathrm{CaCO}}_3$ distributions at the quiescent state through microfluidic chip tests where the bacterial solution (BS) and cementation solution (CS) were initially injected simultaneously from two separate microchannels and subsequently converged in a reaction microchannel. The experiments revealed that the bacterial diffusion within the CS injection area was hindered for a high concentration of calcium chloride (${\mathrm{CaCl}}_2$) (e.g., 0.5 M), whereas diffusion appeared homogeneous for a low concentration of ${\mathrm{CaCl}}_2$ (0.05 M). In addition, the ${\mathrm{CaCO}}_3$ distribution along the width of the reaction microchannel was more uniform for $0.05\mathrm{M}{\mathrm{CaCl}}_2$ than for $0.5\mathrm{M}{\mathrm{CaCl}}_2$. The microfluidic chip tests in this study provided kinetic observations of the MICP process that improved the understanding of the mechanics of bacterial diffusion and ${\mathrm{CaCO}}_3$ crystal growth and their variation with different concentrations of ${\mathrm{CaCl}}_2$.

This paper presents experimental investigation into the effects of particle size distribution of subgrade soil on mud pumping. The results show that subgrade soils with higher fine contents do not necessarily lead to more serious mud pumping. A soil with a higher silt content tends to cause the formation of a less permeable interlayer at the bottom of the ballast, which effectively reduces the particle migration magnitude. Increasing the median particle size ($d_{50}$) or reducing the coefficient of uniformity ($d_{60}/d_{10}$) of the studied sandy silt promotes the migration distance of particles. While mud pumping is essentially an internal erosion problem caused by cyclic loads, existing filter theories do not directly apply to mud pumping. The findings from this study can help selecting proper rail embankment fills to reduce mud pumping.

Use of lightweight cellular concrete (LCC) as backfill for mechanically stabilized earth (MSE) walls in place of the standard aggregate backfill can reduce foundation soil settlement and lateral earth pressure on the back of the wall facing after construction. However, load transfer between reinforcing steel strips and LCC needs to be understood prior to developing a design method for the LCC MSE wall. In this study, eight field pullout tests of five strips embedded in an LCC wall were conducted. Pullout capacity of steel strips in LCC varied with time for the first 14 days and then became constant, whereas the residual capacity remained approximately constant when the age was greater than 3 days. In addition, the pullout capacity of steel strips did not increase proportionally with the strip length.