Journal of Geotechnical and Geoenvironmental Engineering

In deterministic evaluations, liquefaction triggering potential is assessed by comparing the computed factor-of-safety ($FS$) against liquefaction triggering to some minimal acceptable $FS$. While some guidelines are available for selecting the minimal acceptable $FS$, there is no standard value. Herein, Receiver Operating Characteristic (ROC) analyses are used to develop an approach for selecting the optimal minimal acceptable $FS$ (i.e., optimal $FS$) for a project based on the relative costs of mispredictions. Utilizing different liquefaction triggering models and their associated case-history databases, relationships are established between the optimal $FS$ and the ratio of the cost of a false-positive prediction to the cost of a false-negative prediction (i.e., cost ratio, $CR$). Also, by combining the $FS$ data from different models, a “generic” $FS\text{-}CR$ relationship is developed that “averages out” the degree of conservatism inherent to the individual triggering models. Similarly, relationships relating the optimal probability of liquefaction triggering ($PL$) to $CR$ are developed for the probabilistic variants of the triggering models, as well as a generic $PL\text{-}CR$ curve.

Using the generalized Hoek and Brown yield criterion, the stress characteristics method (SCM) was used to evaluate in a very accurate manner the bearing capacity of smooth and rough ring foundations placed over rock media. Failure mechanisms, involving a combination of outward and inward shear zones, with consideration of the stress singularities at the outer and inner edges of the ring, were generated. The complete computational procedure is elaborated, and the computer code, written in MATLAB version 2018a, is available free upon request. To compare the results obtained, the solution is also provided making use of finite-element limit analysis (FELA) using OPTUM-G2 version 2018.07.28. The bearing capacity obtained using the SCM compares very well with the solution on the basis of the FELA, which confirms the rigor of the analysis performed. The failure patterns obtained from the SCM and the FELA were found to be almost identical.

The axial loading test on a geogrid-encased stone column has been simulated using 3D numerical model in the proposed study. The stone column was modeled using the discrete element method (DEM), and the geogrid was modeled by the shell-type encasement using finite difference method (FDM). The column was modeled using nonspherical rigid particles considering the actual shape and size distribution of gravel, which better represents the discrete nature of stone columns. The rationality of the proposed numerical model was successfully verified by experimental results from a previous model test. The complete deformation and failure process of the geogrid-encased stone column has been well captured. The numerical results have been discussed at both the macroscopic and microscopic levels. The stress state of the geogrid-encased stone column never approaches the limiting equilibrium state before the geogrid rupture. The bearing capacity of the geogrid-encased stone column mainly depends on transverse ribs of the geogrid. The force chain network and coordination number evolvements inside the stone column were determined during the complete loading process and related to macroscopic failure behaviors. The parametric analysis indicates that linear relationships can be established between the macroscopic performance of the geogrid-encased stone column and the properties of the geogrid and gravel. The macroscopic and microscopic numerical results in this study can provide researchers improved understanding of the geogrid–gravel system.

Surface wave methods have been extensively employed to estimate time-averaged shear-wave velocity ($V_s$) to $30\mathrm{m}$ ($V_{s,30}$) for seismic site classification. However, the inversion of surface wave dispersion data for $V_s$ profiling is inherently computationally intensive. To overcome the challenge involved in surface-wave inversion, a new method is proposed to directly estimate $V_{s,30}$ from surface wave fundamental-mode dispersion data without inversion. The new method is based on the concept that the phase velocity of surface waves ($V_R$) at a given frequency ($f$) is proportional to the average shear-wave velocity of soils within one-half of the wavelength ($\lambda =V_R/f$). The proposed method starts from calculating the $V_s$ of the top layer as it can be directly estimated from the phase velocity of surface waves whose half wavelengths are smaller than the thickness of the top layer. Likewise, the $V_s$ of the second layer can be deduced from the top layer $V_s$ along with the phase velocity of surface waves whose half wavelengths are within the thickness range of the second layer. Through such a repetition of sequence-deduction, the $V_s\mathrm{s}$ of the other layers can be calculated. This method is verified with five case studies that cover typical geotechnical sites. Results indicate that the proposed method can obtain a similar $V_{s,30}$ with the same site classification for seismic design in comparison with invasive tests and inversion techniques.

This paper investigated the application of the cyclic strain approach to the analysis of ocean wave liquefaction. The threshold shear strain concept was conceived in the early 1980s for the analysis of seismic liquefaction, but there are limited published studies on its application to the ocean wave liquefaction problem. This study was based on the analysis of data from three small-scale wave flume experiments that were compiled from the literature. Resonant column (RC) and bender element (BE) tests were performed on soil samples from one of the flume experiments and used to independently assess the stiffness and threshold shear strain properties. The RC results indicated threshold shear strains ranging from 0.004% to 0.016% at effective confining pressures of 20–100 kPa, which is consistent with values for sands in the literature. Particle contact mechanics was used to extrapolate the RC threshold shear strains to the very low confining pressures in the wave flume soils. The analysis results showed consistency between the threshold values extrapolated from the RC tests and those interpreted from the wave flume data. The results of this study strengthen the use of the threshold shear strain concept for the analysis of ocean wave liquefaction, either as a simple screening tool or in more advanced numerical modeling.

Centrifuge modeling has been considered as an effective means of studying flexural soil–pile interaction, yet the conventional use of elastic material to model an RC pile prototype is unable to reproduce the important nonlinear quasi-brittle behavior. It also remains a challenge to numerically model the soil–pile interaction due to the nonlinearity of both the soil and pile materials. This paper presents a small-scale model RC pile for testing soil–structure interaction under lateral pile head loading in sand within a centrifuge. Accompanying nonlinear finite-element numerical modeling is also presented to back-analyze the centrifuge observations and explore the influence of the constitutive models used. The physical model RC pile is able to (1) reproduce the pile failure mechanism by forming realistic tension crack patterns and plastic hinging and (2) give hardening responses upon flexural loading. Comparisons of measured and predicted results demonstrate that for the laterally loaded pile problem, the load–displacement response can be well approximated by models that do not incorporate strain softening, even though the soil behavior itself exhibits a strong softening response.

This paper investigates the efficacy of recycled-plastic pins (RPPs) for controlling the ground settlement of soft foundation soil. Two field test sections ($6\times 7.5\mathrm{m}$) were constructed over soft soil; one was left unreinforced to use it as a control section, and the other section was reinforced with RPPs. A load transfer platform (LTP), composed of recycled crushed concrete aggregate (RCCA), sandwiched between two geogrid layers, was placed above the RPPs for transferring the load from the embankment onto the RPPs. Vertical pressures, settlements, and pore water pressures were monitored. After 260 days, a maximum settlement of 52 mm was observed for the control section, whereas for the reinforced section, it was 23 mm. Excess pore pressure dissipated faster in the control section. The measured data indicated that the RPPs supported a significant percentage of the embankment load. The in-situ measurements have proven the effectiveness of RPPs in combination with LTP in reducing settlement. The present method can be applied for any embankment construction over soft soil, bridge approaches, and widening of a highway where the foundation soil is unsuitable for regular construction.

This paper introduces a new numerical approach in the analysis of the dynamic interaction between the steel catenary riser (SCR) and seabed in the vicinity of the touchdown zone (TDZ). The interaction between the SCR and seabed is modeled by a series of springs distributed along the SCR length. The pipe-soil interaction (the single spring) is simulated by an elastoplastic model in which the penetration resistance is estimated according to the relation to the yield force on the backbone curve. The backbone curve is calculated according to the current soil undrained shear strength ($s_{u,av}$) at the pipe depth. The $s_{u,av}$ is evaluated by a recently developed effective stress framework in which the effect of soil remolding during pipe dynamic motion can be well captured by formulating within the framework of critical-state soil mechanics. An example of the whole SCR under cyclic displacements induced by the vessel motion for different wave conditions is analyzed using the proposed numerical approach, and the SCR responses in the TDZ, including the embedment, contact forces, penetration stiffness, and structural responses, are discussed.

Global stability analysis is a key component of mechanically stabilized earth (MSE) wall design, especially those constructed over marginal soils. When limit equilibrium analysis is used for MSE wall design, incorrect factors of safety can be predicted depending on the shape assumed for the failure surface. The use of ground improvement, such as aggregate piers (AP), further complicates the analysis. A mobilized bearing capacity (MBC) approach is presented which highlights the direct relationship between the factors of safety for global stability and bearing capacity. Results from the MBC approach are compared with finite element strength reduction analyses for a range of MSE wall geometries and AP replacement ratios. The factors of safety match well for global factors of safety between 1 and 1.5, considering both eccentricity and stress concentration. The MBC approach provides a tool to supplement and refine global stability analyses for retaining walls constructed over improved foundations.

The bearing capacity of square and/or rectangular footings in geotechnical foundation designs traditionally is determined based on experimental observations and/or deterministic analysis assuming uniform soil profiles. However, soils are spatially varying, and this spatial variability can significantly affect the bearing capacity of the foundation soils. Probability-based design methods can address this problem explicitly. However, a full three-dimensional (3D) probabilistic simulation, such as that involving the random finite-element method, generally is prohibitive, because it involves numerous Monte Carlo runs of a complicated nonlinear elastoplastic algorithm. This paper developed and validated an approximate analytical method based on local averaging theory and geometric averages of soil properties directly under the footing. It was found that the theoretical prediction of the first two moments of a square footing bearing capacity agrees very well with crude Monte Carlo simulation. The analytical prediction of the probability of a design failure was validated through simulation and can be used directly in reliability-based designs against bearing failure.

Microbial-induced carbonate precipitation (MICP) has been explored for more than a decade as a promising soil improvement technique. However, it is still challenging to predict and control the growth rate and characteristics of ${\mathrm{CaCO}}_3$ precipitates, which directly affect the engineering performance of MICP-treated soils. In this study, we employ a microfluidics-based pore-scale model to observe the effect of bacterial density on the growth rate and characteristics of ${\mathrm{CaCO}}_3$ precipitates during MICP processes occurring at the sand particle scale. Results show that the precipitation rate of ${\mathrm{CaCO}}_3$ increases with bacterial density in the range between $0.6{\times 10}^8$ and $5.2{\times 10}^8\mathrm{cells}/\mathrm{mL}$. Bacterial density also affects both the size and number of ${\mathrm{CaCO}}_3$ crystals. A low bacterial density of $0.6{\times 10}^8\mathrm{cells}/\mathrm{mL}$ produced $1.1{\times 10}^6$ crystals/mL with an average crystal volume of 8,000 ${\mu \mathrm{m}}^3$, whereas a high bacterial density of $5.2{\times 10}^8\mathrm{cells}/\mathrm{mL}$ resulted in more crystals ($2.0{\times 10}^7\mathrm{crystals}/\mathrm{mL}$), but with a smaller average crystal volume of $450\mu {\mathrm{m}}^3$. The produced ${\mathrm{CaCO}}_3$ crystals were stable when the bacterial density was $0.6{\times 10}^8\mathrm{cells}/\mathrm{mL}$. When the bacterial density was 4–10 times higher, the crystals were first unstable and then transformed into more stable ${\mathrm{CaCO}}_3$ crystals. This suggests that bacterial density should be an important consideration in the design of MICP protocols.

The objective of this study was to investigate the effectiveness of dynamic compaction (DC) on sandy soils with shallow groundwater table in a geotechnical centrifuge. A total of five model tests were conducted on two different soils with fines contents of 0% and 10%, with water and hydroxypropyl methylcellulose (HPMC) as pore fluids. All models were tested at 30 gravities using the 4.5-m radius large beam centrifuge facility available at the Indian Institute of Technology (IIT) Bombay, India. A custom designed and developed in-flight actuator was used in the study, and a tamping energy level of 208 t-m was simulated to replicate the field DC process. The results were interpreted in terms of pore pressure developments and ground vibrations induced during tamper blows by analyzing instrumentation data recorded by pore pressure transducers and accelerometers. Furthermore, digital image cross-correlation (DIC) analysis was applied on photographs of the front elevation of the models captured during the centrifuge tests, and corresponding crater formations, displacement vectors, contours of displacement, and volumetric strains were plotted for quantitative assessment of ground improvement induced by DC. The effectiveness of pore fluid substitution in dynamic centrifuge modeling was investigated in the context of DC using water and HPMC pore fluids. It was observed that the performance of DC on sandy soil without fines was independent of pore fluid type. However, in the case of silty sand with 10% fines, pore pressure developments were found to be significantly different with and without HPMC, indicating the importance of viscous pore fluid substitution for modeling DC on low-permeability soils in centrifuges. For effective application of DC on soils with permeability on the order of $5\times {10}^{-5}\mathrm{m}/\mathrm{s}$ or less, tamping should be executed in passes in order to dissipate excess pore water pressure induced by DC.

There is limited understanding of how frozen fill compacted below freezing air temperatures affects the performance of highway embankments in the Arctic. Fill material needed to construct embankments is typically obtained from borrow sources potentially containing high ice content that makes compaction challenging. Embankment test sections along the recently constructed Inuvik-Tuktoyaktuk Highway (ITH) in the Northwest Territories, Canada, were constructed with frozen fill material and instrumented with thermistor strings to monitor temperatures at different locations within the embankment and the foundation soil. Thermal modeling was carried out using a commercially available finite-element software applying (1) thermal modifiers available from the literature and (2) available climate parameters from weather stations and satellite data for a surface energy balance model calibrated with recorded field data. Thermal model results for the 3-year monitoring period show good agreement with recorded field data for both modeling approaches. With climate change being an important consideration for embankment design, construction, and maintenance in the Arctic, climate modeling scenarios provided by the Canadian Centre for Climate Modelling and Analysis (CCCma) were used to evaluate thermal resilience under near-term and long-term conditions. The results confirm that the design of embankments and maintenance operations need to consider impacts of near-term and long-term climate change in order to maintain the thermal stability of these embankments and to provide adequate resilience against permafrost degradation.

This study presents the use of controlled blasting for the determination of the in situ dynamic response of a sand deposit at a depth of 25 m under effective overburden stresses of approximately 250 kPa. The experiments were performed to establish the suitability of blasting as a seismic energy source for the quantification and evaluation of dynamic constitutive soil properties, including the coupled degradation of shear modulus, $G$, and generation of excess pore pressure, $u_e$, with shear strain, $\gamma$. The ground motion characteristics associated with controlled blasting were quantified, indicating that compression waves operate at frequencies too high to generate significant particle displacements and corresponding strains. The shear waves generated due to near- and far-field unloading of the initial compression wave were found to control the soil response, and were associated with frequencies common in earthquake ground motions. The three blast experiments provide the basis for the in situ observation of constitutive soil properties, including the threshold shear strains to trigger soil nonlinearity and residual excess pore pressure, $u_{e,r}$, as well as changes in constitutive responses as a result of alterations in the soil fabric and geostatic stress state. Field drainage during the experiments was found to exert a significant influence on large-strain $G$, and its effects distinguish the in situ response from those observed in dynamic, fully undrained or constant-volume laboratory experiments. The linear-elastic threshold shear strain, ${\gamma }_{te}$, of the natural sand deposit ranged from 0.001% to 0.002% and the threshold shear strain to initiate $u_{e,r}$, ${\gamma }_{tp}$, ranged from 0.008% to 0.01% for the intact natural deposit. Reduction in normalized $G$ of approximately $0.70G_{\max }$ was necessary to trigger $u_{e,r}$ within the intact natural sand deposit. The generation of $u_e$ in the reconsolidated sand deposit was greater than the intact deposit, with ${\gamma }_{tp}$ reducing to 0.002%–0.003%. The significantly reduced geostatic stress state inferred from shear wave velocity and settlement measurements facilitated comparison of the shear strain–excess pore pressure relationship for vertical effective stresses ranging from 44 to 256 kPa, and confirmed that such relationships are highly pressure dependent.

Dynamic nonlinear effective stress analysis of 45 well-documented liquefaction field case histories provides insights on the seismic response of sites where simplified liquefaction triggering procedures indicated liquefaction effects would be severe but either surface manifestations were not observed or inconsistent amounts of sediment ejecta were observed. The occurrence of sediment ejecta and its severity depend significantly on hydraulic processes after strong ground shaking ceases, which the simplified procedures do not consider. Postshaking advection processes govern the amount of upward seepage–induced artesian flow that determines ejecta severity. The ejecta potential index (EPI) captures these key aspects of the hydraulic processes of liquefaction manifestation. EPI can be sensitive to variables such as hydraulic conductivity, groundwater level, and input ground motions. However, it proves to be a useful index that correlates well to the severity of ejecta manifestation observed in the field case histories. Sites with severe ejecta have high EPI values, and sites without ejecta have low EPI values.

To study the deformation response of soft clay under cyclic loads, five groups of undrained cyclic torsional shear tests were conducted under a stress path with different principal stress direction angles and variations in the deviatoric stress. The development tendencies of strain components, axial stress-strain, and cyclic axial modulus are discussed. Experimental results showed that the deformation characteristics of specimens and the effect of cyclic stress variations on the specimens were significantly different at various principal stress direction angles. Based on the newly proposed parameter involving the distance from the initial point of the soft clay specimen after consolidation to the strength envelope at a fixed principal stress direction angle, a linear relationship between the axial strain and newly proposed parameter was found in consideration of the principal stress direction angle and cyclic stress variation.

A series of short-term puncture tests is conducted to investigate the deformation behavior of a 0.5-mm-thick high-density polyethylene (HDPE) geomembrane on particulate underliners subjected to high water pressures. The influence of some key factors (i.e., type of underliner material, particle size, applied pressure, and loading rate) are evaluated. The results indicate that the applied pressure contributing to the geomembrane damages gradually increases with decreasing particle size. It is observed that the wide void spaces between particles and high pressures are the main reasons for the geomembrane damages. An enhanced mathematical model is established to reveal the relationship between the particle size and peak applied pressure. The proposed model provides a useful tool for selecting the maximum particle size of underliner materials to prevent the geomembrane from being punctured.

Probability distribution models (PDMs) of variables are cornerstones in the performance-based earthquake engineering framework. For liquefiable ground in earthquake-prone regions, the liquefiable layer often is sandwiched between nonliquefiable layers. However, PDMs for thicknesses of these soil layers, particularly the nonliquefiable crust and the liquefiable layer, are not yet well established. To fill this gap, this study leveraged field case history data from different regions to develop empirical PDMs for the soil-layer thicknesses of liquefiable ground. Seventeen probability density functions (PDFs) were examined to identify the appropriate ones that well characterize the thickness uncertainties. It was found that the lognormal PDF is an appropriate choice for either thickness variable at either region of interest. Means and standard deviations of the established PDMs for different regions, such as China, Japan, New Zealand, and the US, were tabulated for the expedience of implementation.

Applying a layer of artificially hydrophobized soil barrier was proposed to minimize water infiltration in landfill covers and hence to reduce the formation of leachate. Existing research has focused on the hydrological behavior of hydrophobized soil, but its effectiveness in reducing or delaying infiltration to the underlying unsaturated soil has rarely been studied, especially under extreme wetting conditions. The objective of this study was to perform a series of parametric infiltration tests to quantify the water flow patterns within hydrophobized barriers and then evaluate their effects on the infiltration characteristics of loosely compacted silty underlying or overlying sand. The barrier was made of silica sand that was hydrophobized by 3% dimethyldichlorosilane (DMDCS; by weight). Constant-head ponding was applied on the soil surface. The test results revealed that the hydrophobized barrier could prevent the underlying soil from an increase in water content as long as the ponding head was less than the water-entry head (WEH) of the barrier. The barrier could become ineffective to prevent percolation when the mass portion of the hydrophobized sand was reduced or when the initial degree of saturation increased because of the reduction of WEH.