Journal of Geotechnical and Geoenvironmental Engineering

Repetitive loading can induce volumetric and shear strain accumulation in soils and affect the long-term performance of engineered and natural geosystems. A hybrid numerical scheme based on the FEM is implemented to analyze problems where a very large number of cycles is involved. The numerical approach combines a classical mechanical constitutive model to simulate the static load and the first load cycle and empirical accumulation functions to track the accumulation of deformations during repetitive loading. The hybrid model captures fundamental characteristics of soil behavior under repetitive loading, such as threshold strains, terminal density, and ratcheting response; it also predicts volumetric and shear strains as a function of the static stress obliquity, the number of load cycles, and the plastic strain during the first load cycle. The proposed numerical scheme is used to analyze shallow foundations subjected to repetitive loads. Results show the evolution of vertical settlement, horizontal displacement, footing rotation, and stress redistribution within the soil mass as the number of load cycles increases. Displacements and rotation are more pronounced as the static factor of safety decreases and the cyclic load amplitude increases.

A variety of real-world levee underseepage problems can best be modeled using an axisymmetric analysis approach. In current practice, axisymmetric levee underseepage analyses are performed using numerical modeling approaches, such as the FEM. In contrast, levee underseepage analyses of planar cross sections are often analyzed using a blanket theory analytical approach, which is quicker and more convenient than numerical modeling. To address this problem, this paper provides a derivation of a series of closed-form blanket theory analytical equations that can be used to perform an axisymmetric levee underseepage analysis. This derivation begins from the governing equation of semiconfined fluid flow beneath a levee in a shallow semiconfined aquifer. The equations that result from this derivation can be used to calculate the total head in the pervious foundation layer and the seepage quantity that passes through the levee foundation over time. Different equations are presented for different seepage directions relative to the axis of rotation and different model boundary conditions. A typical example problem is used to compare results from the axisymmetric analytical equations that are derived with those from axisymmetric finite-element analyses. For this example problem, the analytical equations yield results that are equal to or more conservative than those from the finite-element analysis, where conservative results correspond to greater seepage under the levee and higher heads at the levee toe.

Tests were conducted to assess how permeation with synthetic and real municipal solid waste (MSW) leachate affects the hydraulic conductivity and exchange complex of geosynthetic clay liners (GCLs). GCLs were arranged in a composite barrier configuration for hydration on moist compacted subgrades for 30 or 90 days. After hydration, the geomembrane and subgrade soil were removed and the GCLs were permeated with typical and strong synthetic and real MSW leachates at different confining stresses for 342 to 1,281 days (4.9 to 148.9 pore volumes of flow). For most tests, hydraulic and chemical termination criteria were met (referred to as equilibrium), and in many cases the tests were conducted long after these criteria were achieved. Hydraulic conductivity of the GCLs increased no more than 5.6 times the hydraulic conductivity to deionized water (DIW), even though more than 80% of the sodium (Na) in the bentonite was replaced by other cations [predominantly calcium (Ca) and magnesium (Mg)]. Very long testing times can be required to reach equilibrium, especially at higher stresses. However, the combined effects of stress and cation exchange can be evaluated conservatively and more rapidly by first permeating the GCL to equilibrium at low stress, and then increasing the stress to simulate field conditions. Hydraulic conductivities obtained using this approach are no more than three times hydraulic conductivities obtained at equilibrium under elevated stress. Adding a requirement for equality of effluent and influent cation concentrations results in hydraulic conductivities to MSW leachate representative of long-term conditions.

Italy has a number of regions with mid to high vulnerable areas from a hydrogeological point of view. The causes are the result of both the fragility of territory and the anthropic influence on its continuous modifications. A quantitative landslide risk analysis is then necessary to avoid or reduce human life and property losses. In particular, the prediction of landslide occurrence should be estimated taking into account the uncertainties affecting the analysis process. In this paper, a specific type of landslide, triggered by rainfall and characterized by the viscous behavior of soil, is discussed and analyzed. The goal is to illustrate the applicability of a probabilistic approach, based on Bayesian theorem, which aims at developing an advanced analysis, and to predict slow-slope movements. The proposed methodology relies on the probabilistic calibration of a well-defined, viscoplastic-dynamic model that is able to predict the soil mass displacement evolution from groundwater level inputs and return a value of a mobilized friction angle. Making use of a well-established and highly reliable monitoring database of the Alverà landslide, the model is probabilistically calibrated by the Markov-chain Monte Carlo method. Starting from the prior and the likelihood, this numerical method allows sampling of the posterior, which represents the solution of probabilistic calibration given in the form of probability density functions for each model parameter, including the corresponding correlation structure. Furthermore, the uncertainty related to model predictions is fully described.

This paper presents simplified closed-form analytical solutions that can be used to interpret and predict ground movements caused by shallow tunneling in soft ground conditions. These solutions offer a more comprehensive framework for understanding the distribution of ground movements than widely used empirical functions. Analytical solutions for the displacement field within the ground mass are obtained for two basic modes of deformation corresponding to uniform convergence and ovalization at the wall of a circular tunnel cavity, based on the assumption of linear, elastic soil behavior. Deformation fields based on the superposition of fundamental, singularity solutions are shown to differ only slightly from analyses that consider the physical dimensions of the tunnel cavity, except in the case of very shallow tunnels. This work demonstrates a simplified method to account for soil plasticity in the analyses and illustrate closed-form solutions for a three-dimensional (3D) tunnel heading. A companion paper describes applications of these analyses to interpret field measurements of ground response to tunneling.

This paper considers the practical application of analytical solutions for estimating ground movements caused by shallow tunneling in soft ground using closed-form expressions presented in a companion paper based on linearly elastic and average-dilation models of soil behavior. The analytical solutions express two-dimensional distributions of ground deformations as functions of three parameters: the uniform convergence and relative ovalization of a circular tunnel cavity, and either the Poisson’s ratio or the average dilation angle for elastic and plastic behavior, respectively. This paper shows that the analytical predictions can achieve very good representations of the distribution of far field deformations through a series of case studies in clays and sands. In some cases, the input parameters can be interpreted from a simple calibration to three independent measurements of ground displacements comprising surface settlements above the tunnel centerline and at a reference offset, and the lateral displacement at the spring line elevation, recorded by an inclinometer at an offset of one tunnel diameter from the centerline. However, it is generally more reliable to use a least-squares fitting method to obtain the model input parameters, using all available extensometer and inclinometer data.

This work investigates the seismic compression characteristics of nonplastic and low-plasticity silty sands with varying fines content ($0\le \mathit{FC}\le 60\%$). Cyclic simple shear testing was performed on various sand-fines mixtures at a range of modified Proctor relative compaction levels and degrees of saturation. Aside from the expected strong influence of relative compaction, increasing fines content is found to generally decrease volume change for fines fractions consisting of silts and clayey silts of moderate-to-low plasticity index ($\mathit{PI}\le 10$). With truly nonplastic fines (rock flour), cyclic volume change increases with $\mathit{FC}$. Some materials also exhibit an effect of as-compacted saturation in which moderate saturation levels associated with high matric suction cause volume change to decrease. Additionally, the data consistently demonstrate that vertical strains decrease as overburden pressure is increased in a manner consistent with a previous clean sands model. This paper presents empirical equations to capture these effects, which extend a previous clean-sand volumetric-strain material model to account for the previously unconsidered effects of fines content and saturation.

A probabilistic analysis of vertically and obliquely loaded strip footings resting on a spatially varying soil is presented. The system responses are the footing vertical and horizontal displacements. The deterministic computation of these system responses is based on numerical simulations using the software FLAC3D. Both cases of isotropic and anisotropic random fields are considered for the soil elastic properties. The uncertainty propagation methodology employed makes use of a nonintrusive approach to build up analytical equations for the two system responses. Thus, a Monte Carlo simulation approach is applied directly on these analytical equations (not on the original deterministic model), which significantly reduces the computation time. In the case of the footing vertical load, a global sensitivity analysis has shown that the soil Young's modulus $E$ mostly contributes to the variability of the footing vertical displacement, the Poisson ratio being of negligible weight. The decrease in the autocorrelation distances of $E$ has led to a smaller variability of the footing displacement. On the other hand, the increase in the coefficient of variation of $E$ was found to increase both the probabilistic mean and the variability of the footing displacement. Finally, in the inclined loading case, the results of the probability of failure against exceedance of a vertical and/or a horizontal footing displacement are presented and discussed.

This study presents a centrifuge modeling approach to characterize the transient thermomechanical response of energy foundations during heating-cooling cycles to provide data for calibration and validation of soil-structure interaction models. This study focuses on the response of a scale-model energy foundation installed in an unsaturated silt layer with end-bearing boundary conditions. The foundation response was assessed using embedded strain gauges and thermocouples. Other variables monitored include foundation head displacements, soil surface displacements, and changes in temperature and volumetric water content in the unsaturated silt at different depths and radial locations. Measurements during the initial heating process indicate that the thermal axial stress is greater near the toe of the foundation as a result of the restraint associated with mobilization of side shear resistance along the length of the foundation. The thermal axial strains were close to the free-expansion thermal strain near the soil surface and decreased with depth. The thermal axial displacements calculated by integrating the thermal axial strains correspond well with the independently measured head displacements. The mobilized side stresses calculated from the thermal axial stresses increased with height and were consistent with the shear strength of unsaturated silt. During successive heating-cooling cycles, slight decreases in upward thermal head displacement were observed because of changes in the stiffness of the unsaturated soil from thermally induced water flow away from the foundation and potential downdrag effects. However, little change in the thermal axial stress was observed during the heating-cooling cycles.

The uniqueness and form of the critical state line for sands have been widely debated in the literature when particles crush. In this paper, the large-displacement behaviors of two clean sands and a silty sand are studied using ring shear and triaxial compression shear tests. Significant particle damage occurred in the shear bands of the ring shear tests. At very large shear displacements ($\text{>}10\hspace{0.17em}\mathrm{m}$ in the ring shear tests), particle damage and rearrangement/reorientation were complete in the ring shear tests, and a state of constant shear stress, constant effective stress, and constant volume was achieved in the crushed sand. Accordingly, a new definition is proposed for the residual state of damaged (crushed) sands, which is reached only within the shear band. It is shown that the critical state of the original sand (without particle crushing) and the residual state (with particle crushing) are independent of sand fabric (moist tamping and air pluviation) and consolidation stress ($\text{≈}29–770\hspace{0.17em}\text{kpa}$), and the same critical state is established in ring shear and triaxial compression shear tests. A unique residual state line is proposed for sands when particle damage occurs, which is significantly steeper than the critical state line.

The authors investigated the effects of principal stress rotation (PSR) on the traffic load–induced settlement of subways in soft subsoil. Here, a series of hollow cylinder tests on normally consolidated, medium-plasticity soft clay with and without principal stress rotation were performed along with finite-element modeling and simulation. The results show significant increases in both excess pore-water pressure and cumulative deformation of the normally consolidated soft clay when PSR is present and simulated, and the effects become more pronounced as the maximum effective principal stress ratio or load frequency increases. Under the actual traffic load–induced stress in subsoil below the subway tunnel, the presence of PSR increases the cumulative deformation of soft clay by 9–23% compared with that without PSR. As an approximation, the cumulative deformation of soft clay with the effect of PSR can be estimated by multiplying the deformation derived from the repeated triaxial testing without PSR with the ratio of axial strain between the two tests.

In the 1990s, Bartlett and Youd introduced empirical equations for predicting horizontal displacement from liquefaction-induced lateral spreading; these equations have become popular in engineering practice. The equations were developed by multilinear regression (MLR) of lateral spreading case history data compiled by these researchers. In 2002, these equations were revised and updated to include additional case history data. The regressions indicated that the amount of horizontal displacement is statistically related to the topography, earthquake magnitude, and distance from the seismic energy source. It is also related to the thickness, fines content, and mean grain size of the saturated, granular sediments with corrected standard penetration test blow count values less than 15. This paper proposes to modify the MLR empirical equations by replacing the fines content and mean grain size factors with soil description factors. Such modification allows investigators performing preliminary evaluations to make lateral spread displacement estimates using existing geotechnical data with sparse laboratory measurements. The paper also proposes a methodology to estimate the required geotechnical inputs in the proposed modified MLR equations using cone penetration test data.

A surcharge preloading program for an 8-story hotel building at Philadelphia International Airport in Pennsylvania provided an opportunity to examine the merits of coupled consolidation analysis. Close agreement between the measured and predicted responses in pore pressures, settlement magnitude, and rate are attributed to the use of the modified cam clay model for soft Delaware River organic silt. A conventional consolidation analysis utilizes single volumetric compressibility and permeability coefficients rather than ones which vary with the actual stress level as demonstrated by consolidation testing. This results in an appreciable divergence from the measured values. The modified cam clay model clearly captures the actual nonlinear stress-strain behavior of the soft, organic silt layer.

Continuum-based analyses for laterally loaded piles with rectangular and circular cross sections are presented using solutions that can be obtained quickly without requiring any elaborate inputs for the geometry and numerical mesh. The analysis is developed by solving the differential equations governing the displacements of the pile-soil system derived using the variational principles of mechanics. Parametric studies are performed to investigate the influence of the pile cross-sectional shape, soil layering, pile slenderness ratio, and pile-soil modulus ratio on the response of laterally loaded piles in heterogeneous soil in which the soil shear modulus varies continuously or discretely with depth. The results show that piles with the same second moment of inertia have similar lateral-load response. The lateral responses of piles in two-layer systems were mainly affected by the thickness and stiffness of the top soil layer. Soil layering also influences the lateral response of piles in three-layer soil deposits consisting of two thin layers overlying the third layer. Algebraic equations for estimating the pile-head deflection and maximum bending moment are proposed that can be readily used in design. A user-friendly spreadsheet program is developed as a tool to perform calculations of pile response using the analysis. Numerical examples demonstrating the use of the analysis are provided.

Accurate estimates of soil hydraulic parameters representing wetting and drying paths are required for predicting hydraulic and mechanical responses in a large number of applications. A comprehensive suite of laboratory experiments was conducted to measure hysteretic soil-water characteristic curves (SWCCs) representing a wide range of soil types. Results were used to quantitatively assess differences and uncertainty in three simplifications frequently adopted to estimate wetting-path SWCC parameters from more easily measured drying curves. They are the following: (1) ${\alpha }^w=2{\alpha }^d$, (2) $n^w=n^d$, and (3) ${\theta }_s^w={\theta }_s^d$, where $\alpha$, $n$, and ${\theta }_s$ are fitting parameters entering van Genuchten’s commonly adopted SWCC model, and the superscripts $w$ and $d$ indicate wetting and drying paths, respectively. The average ratio ${\alpha }^w/{\alpha }^d$ for the data set was $2.24\pm 1.25$. Nominally cohesive soils had a lower ${\alpha }^w/{\alpha }^d$ ratio ($1.73\pm 0.94$) than nominally cohesionless soils ($3.14\pm 1.27$). The average $n^w/n^d$ ratio was $1.01\pm 0.11$ with no significant dependency on soil type, thus confirming the $n^w=n^d$ simplification for a wider range of soil types than previously available. Water content at zero suction during wetting (${\theta }_s^w$) was consistently less than during drying (${\theta }_s^d$) owing to air entrapment. The ${\theta }_s^w/{\theta }_s^d$ ratio averaged $0.85\pm 0.10$ and was comparable for nominally cohesive ($0.87\pm 0.11$) and cohesionless ($0.81\pm 0.08$) soils. Regression statistics are provided to quantitatively account for uncertainty in estimating hysteretic retention curves. Practical consequences are demonstrated for two case studies.

This paper presents the influence of construction-induced stress changes on the dynamic soil parameters of Bootlegger Cove Formation (BCF) clays at the site of the Port of Anchorage (POA) expansion project. Results are presented based on numerical simulations of the POA wharf construction and laboratory experimentation where both free-field and postconstruction conditions are reproduced. The postconstruction stability of the foundation clay is considered under both static and dynamic loadings. For the dynamic case, a cyclic triaxial loading equivalent to the contingency-level earthquake (CLE) established for design was used, whereas for the static case, undrained triaxial compression and extension loadings to failure were employed. The results from numerical simulations and laboratory experiments are presented and compared with field measurements and performance data collected during the project construction. The results obtained from specially designed cyclic triaxial probes show the large effects that the construction-induced stresses can have on the dynamic soil parameters and illustrate the importance of adequately considering such effects. Testing protocols and procedures are proposed for quantifying postconstruction soil parameters to better reflect field values and values at small (and otherwise appropriate) strain levels.

Soils containing iron oxides that are derived from chemical weathering are widespread in geotechnical systems. This work studies the effect of adsorbed iron oxides on the shear strength of laboratory-prepared iron oxide–coated sands. Goethite- and hematite-coated Ottawa sands were synthesized in the laboratory via a heterogeneous geochemical suspension-reaction method. Surface roughness parameters and fractal dimension were determined using atomic force microscopy (AFM), which showed that hematite-coated sands exhibited the roughest surfaces. ${\mathrm{N}}_2$-adsorption experiments also helped characterize the mineral surfaces. Shear strength parameters were obtained through consolidated drained (CD) triaxial compression, showing an increase in the critical state friction angle of more than 5% when the sands were coated with iron oxides. Iron oxide coatings also increased dilatancy and decreased contractiveness. The experimental results can be attributed to changes in mass-to-mass concentration and intrinsic soil fabric changes due to the presence of iron oxide coatings, as well as to increased roughness and particle-to-particle interlocking.

An image-based method has been developed for determination of particle-size distributions of coarse-grained soils in the 0.075–2.0 mm range. The percentage of fines is also determined. The test is referred to as sedimaging because it analyzes an image of a soil that has been rapidly sedimented through water to sort the particles by size. The sorting facilitates image analysis based on wavelet transformation. This paper details the sedimaging hardware, image analysis method, and test procedures. Parallel sedimaging and sieving tests on nine soils of different colors, gradations, and particle shapes showed nearly identical results. Sedimaging holds several advantages over sieving, including decreased testing time, lower energy consumption, less equipment maintenance, and improvement of the work environment.

The long-term mechanical behavior of overconsolidated (OC) clays in three-dimensional (3D) stress states plays an important role in many geotechnical problems, such as slope failures. However, previous experimental studies of OC clay were carried out under undrained conditions. This paper presents the results of a series of drained true triaxial tests on normally consolidated (NC) and OC clays. The stress paths were maintained in the same $\pi \text{-}\text{plane}$ with Lode angles of $\theta =0–{60}^{°}$. The test results show that OC clays exhibit positive dilatancy tendencies and greater shear strengths and smaller strains to failure than NC clays. The shear strength and dilatancy are largely influenced by the Lode angle. As the Lode angle increases, the shear strength and dilatancy decrease. The decreasing gradients of shear strength and dilatancy versus Lode angle are almost the same, indicating that the constitutive models for OC and NC clays can share the same rules for strength and dilatancy. The formation of shear bands in the $\theta ={60}^{°}$ specimens appears to have caused the abnormal test results in that case.

The vertical uplift resistance of two interfering rigid strip plate anchors embedded horizontally at the same level in clay has been examined. The lower and upper bound theorems of the limit analysis in combination with finite-elements and linear optimization have been employed to compute the failure load in a bound form. The analysis is meant for an undrained condition and it incorporates the increase of cohesion with depth. For different clear spacing ($S$) between the anchors, the magnitude of the efficiency factor (${\eta }_{c\gamma }$) resulting from the combined components of soil cohesion ($c$) and soil unit weight ($\gamma$), has been computed for different values of embedment ratio ($H\text{/}B$), the rate of linear increase of cohesion with depth ($m$) and normalized unit weight ($\gamma H\text{/}c$). The magnitude of ${\eta }_{c\gamma }$ has been found to reduce continuously with a decrease in the spacing between the anchors, and the uplift resistance becomes minimum for $S\text{/}B=0$. It has been noted that the critical spacing between the anchors required to eliminate the interference effect increases continuously with (1) an increase in $H\text{/}B$, and (2) a decrease in $m$.