Journal of Geotechnical and Geoenvironmental Engineering

Excavation-induced ground movements can have a detrimental influence on adjacent structures and services. These complex soil–structure interactions are affected by a range of factors such as ground conditions, excavation sequence, and the characteristics of the structures. Considerable prior research has been concerned with understanding the ground response during excavation and in evaluating the potential damage to adjacent facilities. A number of case histories have been reported worldwide. Finite-element analysis can be effective in providing insight into the response of the ground and adjacent structures during the entire construction process. Previous studies have shown that observed excavation behavior (e.g., ground movements and retaining wall deformations) can be captured reasonably well in finite-element analysis, provided that certain key modeling aspects are appropriately addressed. This paper extends a previous deep excavation case study in greenfield conditions (i.e., without adjacent buildings and utilities included in the analysis), focusing particularly on the excavation-induced settlements of nearby buildings and buried pipelines. Sensitivity analyses have been conducted to investigate the effects of several aspects on the computed settlements of buildings and pipelines, such as (1) building weight, (2) building stiffness, (3) building foundation type, (4) ground improvement measures, and (5) geometries and material properties of pipelines. Conclusions are drawn for future applications.

The drying phenomenon in clays is a multiphysical process accompanied by alterations in the thermal, hydraulic, and mechanical states of the multiphase system. Reversible and irreversible characteristics of shrinkage deformation have been observed experimentally in clayey soils for different ranges of moisture contents. The kinematics of drying due to evaporation and drying-induced shrinkage can be studied by utilizing a coupled thermo-hydro-mechanical (THM) model. An accurate evaluation of drying-induced shrinkage is needed to investigate the thermal cracking and damage of geomaterials. In this study, we developed a thermoporoelastoplastic constitutive framework assuming a non-associative plastic flow rule that can accurately model the transversely isotropic behavior of stiff natural clays in unsaturated conditions. All material parameters used in the non-associative transversely isotropic constitutive model were calibrated based on experimental observations of Boom clay. Then, the capability of the model was assessed by analyzing the convective drying experiment on natural Boom clay. The comparison of the numerical and experimental results confirms the plausibility of the hypotheses made in this study. The results show that the first stage of evaporation ends rapidly and the falling rate period (second stage of evaporation) is the dominant evaporation mechanism due to the intrinsic hydraulic properties of Boom clay and the high evaporative demand of the environment. The developed model reasonably captures the anisotropic elastic and plastic deformations of the clayey soil during the transient drying process. Numerical results demonstrate that drying shrinkage induces a 30% reduction in porosity in which approximately 82% of the total volumetric deformation in drying-induced shrinkage is irrecoverable (i.e., plastic). Moreover, the results indicate that most of the plastic deformation occurs in the first couple of hours of the drying process, when the soil’s unsaturated condition is in a funicular state (i.e., where capillary pressure is dominant). Finally, the last section of this paper is devoted to a sensitivity analysis of the THM behavior of Boom clay with respect to its elastic and plastic strength. The parametric study shows approximately 10% more reduction in the final surface shrinkage when the difference between the slopes of the drying-induced compression line and the swelling line (i.e., $\lambda -\kappa$) is doubled.

Soil biocementation represents an emerging technique that has dominated the development of sustainable and innovative geotechnics during the past decade. Despite numerous studies focusing on peak strength behavior and the ensuing softening response, less is known about the stress- and time-dependent deformability of biocemented geomaterials even though it remains central for most envisaged applications. This study comprised an experimental campaign on two microbially induced carbonate precipitation (MICP)-treated sands with different initial characteristics. Samples with various calcite contents were subjected to uniaxial and incremental loading and to long-term monotonic loading to evaluate their compressibility and capture the principles of their deformation. Furthermore, the use of the porosity-to-cement ratio, originally developed for artificially bonded soils, is herein evaluated as a parameter to capture and express the behavior of MICP-treated sands. Observations from the incremental loading campaign revealed that for a range of calcite contents between 3% and 8% and for applied stress levels up to 1,000 kPa, MICP treatment significantly enhanced the stiffness properties of the geomaterials and reduced their overall deformability. Medium-grained sand required lower bond contents to achieve a similar compressibility to fine-grained sand and was more compatible with the porosity-to-cement ratio. The effects of time dependency were also assessed under different sustained monotonic loads over a long time ($>75\mathrm{days}$). Under sustained high stresses exceeding the apparent preconsolidation stress, the coefficient of secondary compression reached up to a threefold increase compared with the untreated state. Based on the behavioral characterization, stress and time considerations were shown to be interdependent. The cementation achieved by the treatment shifted a portion of immediate settlement, which was released as delayed deformation after bond breakage took place, depending on loading configuration and bond quality (deposition and imperfections), as determined via microstructural observations.

In this study, the effect of load application point ($z_p$) on the load capacity ($Q_u$) of helical anchors under inclined loading condition was investigated. For this purpose, coupled Eulerian-Lagrangian finite element analyses were performed for various configurations of helical anchor and load inclination angles ($\theta$). The focus was on characterizing the optimum load application point that can most enhance the load capacity of helical anchors. Both inclined loading and load application point significantly affected the load capacity of the helical anchor. For the individual failure-mechanism case, the effect of $\theta$ on $Q_u$ was clearly beneficial in most cases, indicating that the individual configuration is more advantageous when a taut or catenary mooring type is adopted. The load capacity of the helical anchor increased as the load application point moved from the top to certain limit depth, below which the load capacity became reversely decreased with further increasing $z_p/L$. The optimum loading depth was found at $z_p/L=0.625$. The effect of $z_p$ on the pullout capacity was mainly controlled by the horizontal load component. Based on the results of this study, design equations for the load capacity of helical anchors with load application point are proposed.

Closed-form analytical solutions are presented for the critical failure plane angle and maximum total reinforcement force in a geosynthetic-reinforced soil (GRS) retaining wall, as obtained from a general force equilibrium analysis of a triangular soil wedge at the active limit state. The solutions can accommodate variable wedge geometry, pore pressure, shear strength parameters, reinforcement force inclination, surcharge stress, applied loads, and pseudostatic seismic coefficients, and include explicit consideration of reaction forces at the toe of the wall. The soil wedge and facing column are treated as a combined block with a vertical load factor to account for soil downdrag on the back of the column. Verification checks show exact agreement with existing analytical solutions for simplified conditions, including Rankine, Coulomb, and Mononobe-Okabe, and good agreement with experimental data from a large-scale GRS retaining wall test. A numerical example is provided to demonstrate the solutions, compare the results with other methods, and highlight the effects of selected variables. Capabilities and limitations of the method are discussed, and a general design approach is outlined.

This paper reports the results of a series of centrifuge experiments exploring the dynamic response of pile foundations. The model tested in a centrifuge at $50g$ consisted of an isolated pile and two pile groups embedded in a kaolin clay, subjected to a sequence of quasi-sinusoidal waves with different amplitudes and frequencies. The results are back-analyzed through a two-step procedure. First, a one-dimensional ground response analysis is performed, in which the small-strain shear modulus is evaluated using data from air hammer tests, while a literature model is used to account for nonlinearity of soil behavior. Second, a three-dimensional finite-element analysis of the model foundations is carried out using the mobilized soil damping ratio and shear modulus determined from the previous step. The aforementioned procedure allowed to reproduce satisfactorily the response of the model foundations tested in the centrifuge, showing that the response of these models is strongly affected by the inertial oscillation of the cap connecting piles necessary to accommodate the measurement devices and to rigidly connect the piles’ heads of the groups. The same numerical model was then adopted to evaluate the change of seismic motion due to pure kinematic interaction effects by setting the pile cap mass equal to zero. This allowed to check the prediction capability of simplified methods of analysis for the evaluation of the base excitation of pile-supported structures. In addition, a number of issues related to the execution of centrifuge tests aimed at investigating the kinematic interaction between pile and soil are highlighted and discussed.

Large-diameter open-ended piles (LDOEPs) are increasingly being used for support of infrastructure projects. Yet, many of the methods in current use for predicting their capacity are based on studies involving small-diameter piles. The efficacy of eight commonly used pile design methods was explored using a database of 64 load tests on full-scale LDOEPs. Capacities were computed using eight commonly used design methods based on both the standard penetration test (SPT) and cone penetration test (CPT). The calculated capacities were compared with capacities interpreted from load tests using several failure interpretation criteria. The study demonstrated that cone penetration test (CPT)-based methods are somewhat superior to SPT methods, but all methods exhibited scatter between measured and predicted capacities, with the computed capacity off by a factor of two in many load tests. Several plugging conditions were compared for each of these methods. Seven of the eight design methods better predicted pile capacity considering that the piles are unplugged, ignoring contributions of the soil internal friction on the pile inner diameter. These findings suggest that (1) LDOEPs do not plug during static loading, with little contribution of interior skin friction to pile capacity; and (2) LDOEPs do not develop significant end bearing.

A method of practical interest is presented in this study for predicting shallow landslide triggering due to expected rainfall scenarios. The proposed approach is based on some closed-form expressions derived using physically-based models and requires a limited number of material parameters obtained from conventional tests. Two typical triggering mechanisms are considered: in the first case, a landslide is caused by a reduction in suction due to rain infiltration in unsaturated soils; in the second one, a slope failure occurs due to the formation of a water table with consequent generation of positive pore water pressures within the slope. A simple criterion is also provided to establish which triggering mechanism occurs. For each considered mechanism, a rainfall threshold curve is derived, which is formally similar to several empirical intensity-duration relationships proposed in the literature for predicting the occurrence of shallow landslides. However, unlike these empirical relationships, the present threshold curves explicitly depend on basic parameters such as slope geometry, soil properties, and pore water pressure existing at the depth of the potential slip surface before the rainfall. The proposed approach is also applied to well-documented case studies to assess its predictive capacity.

Analytical solutions for axial displacement, strain, and stress in a single semifloating energy pile embedded in a layered soil profile subjected to thermal and mechanical loads were derived. An analytical solution for the location of zero displacement, also known as a null point, was derived for a pile subjected to thermal load. It was shown that the location of the thermal null point corresponds to the location of the maximum magnitude of thermal axial stress. It also was shown that the location of the null point moves toward the pile tip as the stiffness of the bedrock below the pile tip increases. The analytical solutions were validated against in situ full-scale energy pile tests. The solutions along with the validation process delineated the load transfer mechanism in energy piles subjected to thermal, mechanical and combined thermomechanical loads embedded in a four-layer soil profile. Flowcharts delineating the procedures for obtaining the analytical solutions for a single energy pile embedded in an arbitrary number of layers, and subjected to thermal and mechanical loads are provided. Although the continuity of stresses and displacements at the interface of different soil layers is maintained, displacement, strain, and stress diagrams exhibit a lack of smoothness, the amount of which depends on the difference in the stiffness of these layers. In summary, the presented solutions provide a rational, mechanics-based framework for advancing the understanding of thermomechanical response of energy piles that not only is essential for analysis and design, but ultimately contributes to a wider use of energy piles and increased sustainability of civil engineering infrastructure.

One of the fundamental decisions when performing one-dimensional (1D) site response analyses (SRA) involves the selection of the depth and dynamic properties of the elastic halfspace (EHS). This boundary condition assumes linear and homogenous material underlying the soil column for an infinite depth. This assumption implies that waves refracted into the EHS are fully absorbed, and as a result, energy from waves that are potentially reflected back toward the surface from deeper impedance contrasts in the actual geologic profile are not accounted for in the SRA. If a strong soil-rock seismic impedance contrast is present at the site of interest, the EHS boundary is typically set at that depth. However, the actual geologic profile below this impedance contrast may not be in accord with the assumed properties of the EHS, which can lead to systematic errors in the SRA. An analytical expression to quantify these errors is derived in this study, verified using an idealized three-layer profile, and compared to case studies of nine real sites in Charleston, South Carolina. Our results show that the presence of a single strong impedance contrast does not suffice as the sole condition to define the EHS boundary. Frequency-dependent errors in site amplification associated with the assumptions inherent to the EHS used in the SRA can be evaluated as a function of multiple impedance contrasts present in the profile. Smaller errors are associated with strong impedance contrasts at shallower layers and/or minimal impedance contrast among layer interfaces at depth. We also find that strong impedance contrasts located at great depths within deep soil deposits introduce nonnegligible errors to site response results.

Induced partial saturation (IPS) is considered to be one of the most promising technologies to tackle soil liquefaction risk. The mitigation of the liquefaction susceptibility of loose partially saturated sandy soils is linked to the high volumetric compressibility of the gas or air bubbles entrapped in the continuous water phase. Based on a large amount of experimental data, a new formulation of the potential volumetric strain (${\epsilon }_v^{*}$) of nonsaturated soil is introduced to overcome some experimental inconsistencies linked to the possible dissolution of the air bubbles, that may not be neglected at the laboratory scale if cyclic loads are applied with low frequencies ($<1\mathrm{Hz}$). Gas dissolution increases the volumetric strains, and if neglected may lead to unconservative estimates of the beneficial effect of desaturation on liquefaction potential. The experimental results of this study also showed that the difference in liquefaction resistance between partially saturated and fully saturated soils depends only on the volumetric component ($E_{v,\mathrm{liq}}$) of the specific energy spent to attain liquefaction. Such a synthetic state parameter satisfactorily allows predicting the liquefaction resistance curves of partially saturated sands.

Lateral spreading of an interlayered deposit adjacent to a meandering stream channel in Wufeng, Taiwan, during the 1999 Chi-Chi Earthquake is evaluated using two-dimensional (2D) nonlinear dynamic analyses (NDAs) with geostatistical modeling of the subsurface to assess their ability to approximate the observed magnitude and spatial extent of ground deformations, as well as identify the key factors and mechanisms that most contributed to the overall system response. In-situ data from borings and cone penetration tests (CPTs) depict thinly stratified overbank deposits of low-plasticity silty sands, silts, and clays, interlayered with laterally discontinuous channel-deposited sands. The three-dimensional (3D) subsurface is simulated using transition probability-based indicator geostatistics, conditioned on available CPT data and geological inferences. The NDAs are performed using the PM4Sand and PM4Silt constitutive models, within the FLAC finite difference program. Sensitivity analyses are performed to understand the influence of uncertainties in the stratigraphy, channel conditions, soil properties, input ground motions, constitutive model calibration protocols, and numerical boundary conditions, as well as the performance of alternate channel transects. Most analysis cases generally matched the maximum displacements observed near the channel but overestimated the extent of displacements away from the channel. The most favorable results were largely influenced by nonstationary stratigraphic trends and cyclic softening of fine-grained soils, in addition to the liquefaction of coarse-grained soils. This case history demonstrates the capabilities and limitations of current subsurface and NDA modeling procedures for predicting ground deformation patterns.

This paper investigates the effects of soil particle size on the measurement accuracy of single-point type tactile pressure sensors when used for measuring soil contact stresses. Sensors with two different diameters (${\mathrm{D}}_{\mathrm{sens}}$) are integrated into an oedometer cell. Granular materials with a wide range of particle diameters (${\mathrm{D}}_{50}$) and angularities (from rounded to irregular shaped) are evaluated, resulting in a wide range of ratios of ${\mathrm{D}}_{\mathrm{sens}}/{\mathrm{D}}_{50}$ from 2.6 to 105.8. The test results show that the soil particle size significantly affects and exponentially correlates with the measurement accuracy of the sensor. A threshold ${\mathrm{D}}_{\mathrm{sens}}/{\mathrm{D}}_{50}$ of 10.5 is identified for the sensor, beyond which the error is less than 5%. It is also shown that even for ratios of ${\mathrm{D}}_{\mathrm{sens}}/{\mathrm{D}}_{50}$ as large as 40, an error of approximately 2% can be observed, which is intrinsic to the sensor.

Postshaking soil volumetric strains of liquefiable soils are of technical interest because they cause a relevant part of the total settlements experienced by the site of interest. In the case of liquefiable intermediate soils, such as sandy silts or silty sands, reconsolidation volumetric strains are affected by the amount of fines. The technical note reports the results of laboratory cyclic undrained tests carried out to study liquefaction resistance and postliquefaction volumetric behavior of sand-silt mixtures reconstituted with increasing amount of nonplastic fines [$0<\mathrm{fines}\mathrm{content}(\mathrm{FC})<20\%$]. The test outcomes indicate that the equivalent granular void ratio ($e^{*}$) can be successfully adopted to quantify the volume reduction of sand-silt mixtures as long as the soil matrix is ruled by the grains of sand. An analytical relationship between $e^{*}$ and the volumetric strain is finally proposed to be of technical help in predicting the effects of reconsolidation in intermediate soils.

The semipermeable membrane behavior of clay effectively reduces solute flux and therefore can be beneficial in clays used as barriers in chemical containment applications. Except for geosynthetic clay liners (GCLs), the membrane behavior of bentonite-amended soils has been evaluated only at a relatively low bentonite content (BC) ($\le 20\%$). Kaolin–bentonite mixtures with a BC ranging from 0% to 37.5% were tested for membrane behavior using closed-system (no-flow) boundary conditions. The membrane efficiency coefficient $\omega$ was derived from the measured chemico-osmotic pressure differences induced across the specimens under a concentration difference of 20-mM KCl. The $\omega$ of the kaolin–bentonite mixtures increased from 0 to 0.197 with increasing BC. The trend of $\omega$ with increasing BC could be described in three stages: initial stage, transitional stage, and residual stage. The results indicated the occurrence of a threshold BC above which additional bentonite had limited effect in terms of membrane behavior. The threshold BC in this study was 28.6% for the given test conditions.