International Journal of Geomechanics

Matric suction is one of the important variables used to characterize the deformation behavior of unsaturated soil. The stress-strain relationship and the governing differential equations are the two elements in which suction is incorporated in the development of mathematical models for the dynamics of unsaturated soils. In this paper, a simplified finite-element model was used to understand the effect of initial suction and deformation-induced suction variation in the static and dynamic behavior of silty and clayey soils. The simplified finite-element model was developed by neglecting the relative acceleration and velocity terms associated with water and air phases in the fully coupled governing differential equations. The stress-strain behavior of the solid skeleton was represented by linear elastic model, a simple model to explain the computed responses using basic theory. The suction-degree of saturation relationship was modeled by the Brooks and Corey model. Simulation results showed that the initial degree of saturation has significant influence on the behavior of clayey soil compared with silty soil. It is also observed that the effect of matric suction in the Bishop’s effective stress equation is significant if the clay and silt are relatively soft.

Tensile strength of soil plays a decisive role in formation/initiation of cracks and their propagation, and its knowledge is essential to study and analyze the stability of earth-fill dams, slopes, embankments, highways, airfield pavements, deterioration of cricket pitches, and development of ice lenses during freezing. Many researchers have worked on determination of tensile strength of soil, and many methodologies and subsequent correlations between the tensile strength and basic properties of soil have been developed and reported. However, these methodologies are time-consuming and yield results that are soil specific. Further, these studies either neglect the effect of overall soil properties or the water content of soil, which are the most crucial parameters affecting tensile strength. An undermined fact is that there are no easy to adopt methodologies or generalized relationships available in the literature that would yield tensile strength of soil quickly and precisely. As such, to address this issue, a simple methodology for determining the tensile strength of soil, based on its penetration resistance, has been proposed, and its utility and efficiency has been demonstrated.

This paper presents numerical models and mathematical formulations to predict the pullout capacity of anchor plates with different inclination angles embedded in clay. The models were developed based on the failure mechanism deduced from laboratory testing and utilize the Mohr-Coulomb yielding criteria. Expression was given to estimate the maximum pullout resistance of plates with different dimensions and inclination angles embedded in various clayey soils. A comparison between results of finite-element analyses has been performed to find out the effect of different parameters. New two-variable functions have been presented to show the relationship between pullout resistance and embedment ratio with different inclination angles. In addition, an interesting relationship among pullout capacities of anchor plates at different inclination angles was found, and a new concept, ellipse of pullout capacity, has been pronounced. Finally, a new theory has been introduced to predict the pullout capacity of any anchor plates with different inclination angles and various depths, without any computer analysis and just by using the new proposed theory.

Collapsible soil exhibits considerable strength when it is dry, but when it is inundated, it loses its strength and experiences significant volume reduction. Foundations on collapsible soils subjected to inundation may experience sudden settlement without any increase in the in situ stress level. Pile foundations are often used to penetrate layers of collapsible soil to transfer the load to a lower, stronger soil layer. Nevertheless, because of indentation, these piles may experience negative skin friction, which may lead to significant reduction in the pile capacity, or perhaps separation of the pile from its cap. In the literature, although several theories can be found dealing with the design of pile foundations and the prediction of negative skin friction on these piles, little to none was found to estimate the negative skin friction because of the sudden collapse of the surrounding soils. This is mainly because of the difficulties associated in modeling collapsible soil experimentally or numerically. This paper presents a numerical model, which is capable of incorporating the effects of inundation of collapsible soil, and the negative skin friction on axially loaded vertical piles. The model uses the theories of the unsaturated soil and soil-water characteristic curve to estimate the effect of soil suction because of progressive inundation. The procedure takes place by estimating the change in the soil properties and the irrecoverable soil-volume change during inundation. The paper also presents the results of laboratory tests conducted on a single pile driven in collapsible soil subjected to inundation. The measured values of the negative skin friction compared well with the predicted values from the numerical model presented. The pile design guideline is also presented to assist designers in predicting negative skin friction because of inundation. Furthermore, the theory developed can be used to evaluate the condition of an existing pile foundation driven in collapsible soil and to establish the remedies needed to avoid catastrophic failure.

In slope engineering, soils are ordinarily in an unsaturated state. Today the application of unsaturated soil mechanics theory to slope stability analysis has become an essential point in geotechnical engineering research. To explain the relationship between matric suction and soil structure with slope stability (via the pulling-out effect), reasonable finite-element (FE) modules can be created. By using FE analysis (which includes the existing soil parameters), the stability of residual soil slope can be simulated under different water contents (via changes in matric suction) and soil structures (via different $\mathrm{\Phi }$ values). Inferring from the soil-water characteristic curve obtained from previous work, the influence of matric suction on unsaturated soil slope is determined. The importance of matric suction and soil structure is discovered during the root pulling-out analysis. The results show that because of increasing matric suction in unsaturated soil (which is the result of the decreasing degree of saturation), the required force during the pulling-out process (root anchorage) and consequently stress-distribution capacity will be increased, and the safety factor of the soil slope is amended. However, changes in soil friction angle do not affect root anchorage in roots with a sharp deviation angle (53°); for a root with a steep deviation angle (15°), as the soil structure improves by means of increases in the internal friction angle, the forces needed to determine the pull out angle, and accordingly, the stress-distribution capacity, are modified, and the safety factor is improved.

A solution algorithm based on three-dimensional (3D) finite-element analysis is presented to study the dynamic response of concrete pavements subjected to moving loads. The pavement is discretized by 20-node isoparametric brick elements. The supporting soil medium is idealized by the elastic continuum model. Kelvin elements are attached to the transmitting boundary separating the near field and far field of the infinite soil medium in the vertical and longitudinal directions. Three-dimensional, 16-node infinite elements are attached to the transmitting boundary in the longitudinal direction to simulate the infinite soil medium in vehicle traverse direction. The moving vehicle is modeled by a mass supported by a linear spring and dashpot assembly simulating the vehicle suspension system. The vehicle-pavement interaction force is modeled with a Dirac-delta function. The dynamic equilibrium equation is solved by applying the Newmark-Beta integration scheme. The effects of vehicle-pavement interaction, pavement thickness, and soil parameters on the dynamic response of pavement are investigated by conducting a parametric study. It has been observed that the dynamic interaction between the moving load and the pavement has a significant effect on pavement response.

The hydraulic deposition process linked to tailings dams normally presents some technical deficiencies mainly because of the lack of control of hydraulic parameters. Problems of instability in tailings dams usually arise from poor management practices, such as poor decant pond control, in addition to the material being placed randomly. Hydraulic parameters, such as the flow rate and concentration of the slurry, play an important role in the formation of hydraulic fills. Grain size, distribution, segregation, and density, and slope inclination are the main characteristics of tailings dams, which are affected by the hydraulic parameters of the slurry. To investigate these factors, an experimental apparatus [hydraulic deposition simulation test (HDST)] was used to simulate the hydraulic deposition process in the laboratory, where all variables that could affect the phenomenon could be controlled carefully. The HDSTs using different flow rates and concentrations were carried out using the iron waste from the Morro Agudo Mine, Minas Gerais, Brazil (operated by Vale). The results presented in this paper are mainly related to the segregation patterns, mean grain sizes, specific gravities, and densities obtained along the small-scale deposited beach in the HDSTs. The main objective of this investigation was to analyze the influence of hydraulic deposition parameters on the formation process of hydraulic fills, focusing on segregation and its importance to density and porosity values. Moreover, a mathematical model was developed to describe and simulate the mechanism of formation of granular tailings dams based on momentum and continuity equations of the fluid and sediments (quartz and iron). The model takes into account the main external variables (slurry concentration and flow rate) and internal variables (such as mean particle size, grain density, and relative percentage of iron and quartz) related to the slurry mixture. The analytical and numerical results of the model were compared with the deposition profiles obtained by the HDST.

The load deformation and failure behavior of shallow footings can be described in a macroelement formulation. This paper deals with the study of the failure surface and the definition and validation of plastic load deformation by single surface hardening models. The straightforward application of the plasticity theory to the soil-foundation system makes it possible to extend the given expression for the case of unsaturated soils. This paper studies a small-scale footing test on unsaturated sand for the formulation of the elastoplastic macroelement of shallow footings under a centrally applied vertical load. The influence of soil suction on different parameters associated with the macroelement is studied and calibrated against experimental results. The presented model shows good agreement with the experimental results. Finally, the limitations and still open questions of the approach are discussed in detail.

In this paper, the authors review recent applications of an integrated numerical modeling approach based on the analysis of the mechanical behavior of discrete systems. The numerical analysis includes both a more realistic representation of fracture networks and the simulation of rock mass behavior as a combination of failure through intact rock and displacement/rotation along predefined discontinuities. Selected examples are presented with respect to a variety of engineering problems, including shear testing, failure of hard-rock pillars, slope stability, and block/panel cave mining. The results clearly illustrate the importance of including natural jointing to better capture rock mass behavior in response to loading and unloading. Particular emphasis is given to modeling cave development and surface subsidence, and the proposed numerical method is shown to capture fully the complex rock mass response to caving associated with multi lift extraction. Whereas the use of relatively complex numerical models is progressively becoming widespread in industry, this paper also reviews how numerical simulations of rock mass behavior strongly depends on the geological assumptions used to build the underlying discrete fracture network model and the mechanical properties of the natural discontinuities. Accordingly, a correct balance among engineering judgment, field characterization, and numerical modeling should always be maintained to reduce model uncertainty.

There are several factors that influence the quality of an asphalt pavement. While pavement design, material selection, and environmental parameters play a big role in the quality and useful life of the pavement, adequate quality control during the compaction process is also necessary to achieve the desired quality. Previous research has addressed the effect of material selection, pavement design and construction, and environmental factors on the long-term performance of asphalt pavement. However, very little work has been done to address the effect of the compaction process on the quality of pavement. A proper understanding of the interaction between the roller and an asphalt pavement is necessary to develop closed-loop control algorithms for intelligent compaction (IC) of asphalt pavements. While several variants of IC techniques are being offered in the market, there is a need for an accurate dynamical model of the compaction process to validate these methods. In this paper, a viscoelastic-plastic (VEP) model of an asphalt pavement is developed that can effectively represent the dynamical properties of the asphalt mat during compaction. This model is then integrated with a mathematical model of a vibratory compactor to study the response of the coupled system during compaction. The VEP model is based on Burger’s model and is used to represent the dynamical properties of the asphalt pavement. The parameters of the model are first estimated from the dynamic modulus master curves of the asphalt mix. These parameters are then continuously updated to accurately represent the properties of the asphalt mat during compaction. Detailed mathematical equations are developed that relate the changes in the asphalt mat to the vibratory response of the roller during compaction. Numerical simulation of the VEP model shows that the response of the coupled system can be used to study the compaction of asphalt pavements. Comparison of the simulation results with data gathered during construction of asphalt pavements indicate that this model could serve as a theoretical foundation for intelligent compaction of asphalt pavement.

In this study, a three-dimensional microscale framework utilizing the discrete-element method (DEM) is presented to analyze the seismic response of soil-foundation-structure systems subjected to three-directional base motion. The proposed approach is employed to investigate the response of a single lumped mass on a square spread footing founded on a dry granular deposit. The soil is idealized as a collection of spherical particles using DEM. The spread footing is modeled as a rigid block composed of clumped particles, and its motion is described by the resultant forces and moments acting upon it. The structure is modeled as a column made of clumped particles with a concentrated mass specified for the particle at the top. Analysis is done in a fully coupled scheme in time domain while taking into account the effects of soil nonlinear behavior, possible separation between the foundation base and soil because of rocking, possible sliding of the footing, and dynamic soil-foundation interactions. A technique to idealize several base boundary conditions to mimic rigid and elastic rock as well as an infinite medium is also presented. Microscale energy dissipation in the soil deposit in the free field and in the presence of the structure is quantified. Simulations were conducted to investigate the response of the deposit with and without the structure to various scenarios of multidirectional shaking patterns. Vertical motion amplification in the free field was similar to that of shear wave propagation. However, there was less nonlinearity for vertical motion than there was for horizontal motion. Lateral motion had a small impact on the amplification of the vertical input motion. The inclusion of vertical motion did not influence the amplification of horizontal motion at frequencies far from the resonance frequency of vertical motion.

The ultimate bearing capacity of strip foundations in the presence of inclined groundwater flow, considering both upward and downward flow directions, has been determined by using the lower bound finite-element limit analysis. A numerical solution has been generated for both smooth and rough footings placed on frictional soils. A correction factor ($f_{\gamma }$), which needs to be multiplied with the $N_{\gamma }$-term, has been computed to account for groundwater seepage. The variation of $f_{\gamma }$ has been obtained as a function of the hydraulic gradient ($i$) for various inclinations of groundwater flow. For a given magnitude of $i$, there exists a certain critical inclination of the flow for which the value of $f_{\gamma }$ is minimized. With an upward flow, for all flow inclinations, the magnitude of $f_{\gamma }$ always reduces with an increase in the value of $i$. An example has also been provided to illustrate the application of the obtained results when designing foundations in the presence of groundwater seepage.

To analyze the pressuremeter test results, the medium around the probe is modeled by a clay hollow cylinder subjected to external and internal uniform pressures. However, assuming that during the test the medium strains around the pressuremeter test cavity are homogeneous results in an oversimplification of the problem. A new analysis method is proposed based on an energy approach concept. The objectives are to determine the outer radius of the clay hollow cylinder that models a normally consolidated clay medium idealized in undrained conditions and to express the clay behavior by the effective stress path and the stress-strain relationship. At the position of three particles across such a cylinder, the developed excess pore water pressures were measured during testing. The analysis showed that the development of greater excess pore pressure than the circumferential stress in compression indicates the critical state and that the testing rate has a negligible influence on the deduced critical state. Thus, the undrained shear strength at the level of testing underground can be obtained.

The concept of an open pipe pile with a gravel plug is used to develop a new short rigid composite caisson foundation for floodplains and lowlands. It consists of a shallow pipe or caisson, sunk to the desired depth by conventional sinking techniques; the soil within the caisson shaft is removed; and granular material is filled in and compacted to enhance the stability and load-carrying capacity. The caisson shaft is considered to be rigid, undergoes rigid body translation, and hence is analyzed as an incompressible cylinder, whereas the core inside is treated as a compressible pile. The soil displacements are calculated at the midpoints of the outer surfaces of each element and at the centers of the bases of the caisson shaft and the granular core by numerically integrating Mindlin’s solution for a vertical point load inside a semiinfinite medium. A parametric study is carried out to bring out the effects of various parameters on the load sharing, the shear stress distribution, and the settlement of the proposed foundation.

The behavior of axially loaded skirted shallow foundations resting on sand was studied using an extensive numerical analysis. Surface, pier, and skirted square foundations resting on sand with different shear strength properties were utilized in the analysis. A physical model testing, although on much smaller scale, was also carried out to support the numerical analysis results. The effects of foundation size, shear strength of sand, and skirt depth on bearing capacity and settlement of skirted foundations were assessed. The results of this study revealed that skirted foundations exhibit bearing capacity and settlement values that are close, but not equal, to those of pier foundations of the same width and depth. The enhancement in bearing capacity of shallow foundation increases with increasing skirt depth and decreasing relative density of sand. Settlement reduction may exceed a value of 70% in the case of having skirt-depth/foundation-width of 2.0. Charts and equations are presented to estimate bearing capacity and settlement of skirted shallow foundations in terms of those of surface foundation and skirt-depth/foundation-width.

This study presents results from the finite-element analysis of a well-instrumented and well-monitored 11-m-high cut slope in Zaoyang, Hubei, China, subjected to rainfall infiltration. This analysis requires simultaneously computation of the deformation and the groundwater flow with time-dependent boundary conditions (fully coupled flow-deformation analysis). Based on the available data, the hydraulic parameters required for the applied Van Genuchten models were estimated. The agreement achieved in pore-water pressures and groundwater levels between measurement and analysis using the FEM can be considered very reasonable for the full time period monitored.

The pullout resistance of soil nail is a key parameter in soil nailing design. Pullout resistance is affected by many factors, such as overburden pressure, grouting pressure, soil dilation, and degree of saturation of soil. Because of the complexity of the pullout mechanism, some factors have not been well incorporated in the current soil nail design methods. In this study, Bayesian analysis is performed to investigate the relative importance of several key factors and to build a new design formula to estimate maximum pullout shear stress of grouted soil nails. By using a series of laboratory soil nail pullout test data, Bayesian analysis is performed to select a predictive formula with suitable complexity and to identify its parameters. It is found that the most important factors are the degree of saturation and the product of grouting pressure and overburden pressure. It is shown that the proposed optimal model exhibits significantly stronger correlation with measurements than the existing effective-stress method for laboratory and field tests.

Nonuniform, initial, excess pore-water pressure distributions in the horizontal direction will have a different impact on the consolidation behavior of the soil layer, when compared with the uniform pore-water pressure distributions discussed in the literature. In the current study, various practical instances in which the nonuniform, axisymmetric, horizontal distributions of pore-water pressure occur are identified. The influence of these distribution patterns on the consolidation response of a cylindrical soil layer draining only at its peripheral face is analyzed analytically using a simple series solution method and by finite-element analysis using PLAXIS. From the $U_{\text{avg}}\text{-}T$ curves and pore-water pressure isochrones developed, it is observed that the uniform pore-water pressure assumption overestimates the degree of consolidation achieved for various pore-water pressure distribution conditions and important information about pore-water pressure redistribution is overlooked. Incorporating appropriate initial pore-water pressure distribution will enable realistic estimates of the degree of consolidation to be made.

When an impact source is applied to the top of a pile, the waves near the top exhibit strong three-dimensional characteristics. When an anomaly is locally distributed near the top of the pile (shallow anomaly), there are some blind areas on the top, where the waves scattered from the anomaly are very weak or absent. The scattered waves cannot be analyzed by the widely adopted theory of one-dimensional stress waves. When the ratio of the characteristic wavelength of the pulse to the radius of piles is large, the tip reflections approximately behave as the plane waves. The upward tip reflections are reflected at the top. These newly formed second incident waves will be reflected at the shallow anomaly. These reflections from the locally distributed anomaly can be approximately regarded as the plane waves, detected by the receiver at any position of the top and analyzed based on the one-dimensional theory. It can be concluded that with the help of the reflections following the tip reflections, it could be possible to detect shallow anomalies more reliably.

One of the key factors in the time domain boundary element method (BEM) for dynamic poroelasticity is an applicable fundamental solution of the governing differential equations. With the completion of the fundamental solutions, this paper is dedicated to the simple time domain traction and fluid flux fundamental solutions for the three-dimensional (3D) $u\text{-}p$ formulation of saturated porous media where fluid and soil particles are assumed incompressible in comparison with the compressibility of the soil structure. First, the explicit Laplace transform fundamental solutions are obtained from the governing differential equations which were written in terms of solid displacements and fluid pressure. Subsequently, the closed form time domain traction and fluid volumetric flux fundamental solutions are derived by analytical inversion of the Laplace transform solutions. Finally, a set of numerical results are presented which demonstrate the accuracy and some salient features of the derived analytical transient traction and fluid flux fundamental solutions.

Even though numerical procedures have been tremendously enhanced over the last years, analytical closed-form solutions are of special interest to water resources scientists. In general, these solutions are used to check the consistency and validate numerical routines. Bibliographical research reveals that up-to-date analytical solutions only take into account one-dimensional (1D) advection, even when three-dimensional (3D) dispersion is considered. This assumption creates an axis dependency because the flux is assumed to be parallel to one of the three possible orthogonal directions, which does not apply to all practical situations in which diagonal advection is present. In this work an analytical solution is derived for the 3D advective-dispersive equation (ADE) by means of Fourier and Laplace integral transforms. The solution allows the contaminant plume to move angularly with respect to the coordinate axes.

This article adopts two data mining techniques, support vector machine (SVM) and least-squares support vector machine (LSSVM), for prediction of soil electrical resistivity based on soil properties and thermal resistivity. Two models (Model I and Model II) are developed. Model I uses the percentage sum of the gravel-size and sand-size fractions (%) and thermal resistivity ($R_T$) as input parameters. Model II uses gravel-size and sand-size fractions (%), degree of saturation (%), and thermal resistivity ($R_T$) as input parameters. Equations have been also developed for the determination of the soil electrical resistivity ($R_E$) of soils. The results are compared with an artificial neural network (ANN) model. This study proves the capability of SVM and LSSVM for prediction of the ${\text{R}}_{\text{E}}$ of soils.