International Journal of Geomechanics

An extensive program of laboratory model tests was undertaken to study the effect of slope and loading direction on laterally loaded piles in cohesionless soil. The paper includes studies of the effect of distance from the crest of the slope (both slope side and embankment side), soil properties, and loading direction (both forward in the direction of the slope and reverse loading). The pile lateral capacity in sloping ground was compared with that in horizontal ground. From the experimental investigation, it is observed that when piles installed in sloping ground undergo forward loading, lateral capacities of the piles are almost reached at 8% of the pile diameter in loose-to-medium dense soil and 16% of the pile diameter in dense soil. If the pile is placed $\text{>}15$ times the pile diameter away from the slope crest within the embankment, the influence of slope in the lateral-load capacity is almost negligible under both forward and reverse lateral load.

Understanding the mechanism of fluid flow through a rock mass (intact rock with discontinuities) is essential for safe and economical construction of the structures that are located in the hard or crystalline rocks. In these rocks, fluid flow occurs mainly through interconnected voids or fracture network, which in turn is governed by the flow properties of the fractures or the most prominent single fracture. However, simulating fluid flow through a fracture network, which is a conglomeration of several individual fractures, is quite intricate and difficult. Hence, focusing on characteristics of the fluid flow through a single fracture under varied confining stress becomes an excellent stepping stone. In addition, collection of the undisturbed rock samples from the deep locations and creation of the fracture(s) for laboratory testing is a cumbersome task. To overcome these limitations, a methodology to simulate flow of water through a fractured rock mass using an analog material, paraffin wax, imbibing a single fracture was developed and its details are presented in this paper. This methodology facilitates easy simulation of the flow through a fracture of certain aperture. Based on the study, it was demonstrated that the Reynolds number is quite sensitive to the fracture aperture and the base pressure, and there is a critical base pressure, beyond which transition in laminar to turbulent flow occurs. It is believed that such studies will be quite handy, useful, and economical for studying fluid flow through the rock mass.

The lateral spreading of backfill soil caused by displacement of gravity-type quay walls is a major concern for geotechnical engineers. This paper evaluates the efficiency of a technique for mitigation of damage to quay walls, which involves densification of loose sand around the toe. The beneficial and unfavorable effects of densification of sand of different locations of the gravity-type quay walls are also answered. For these purposes, numerical simulations (using a finite-element code) and shake table tests were conducted. From numerical simulations and model tests, it was observed that the displacement of a gravity-type quay wall occurred mainly because of shear strain in the foundation. It was also found that the densification of soil at the toe could mitigate the quay wall damage significantly.

This paper presents the three-dimensional discrete element method (DEM) that was used to study the shear behavior of fresh and coal fouled ballast in direct shear testing. The volumetric changes and stress-strain behavior of fresh and fouled ballast were simulated and compared with the experimental results. Clump logic in particle flow code in three dimensions (${\text{PFC}}^{3\mathrm{D}}$) incorporated in a subroutine was used to simulate irregular-shaped particles in which groups of 10–20 spherical balls were clumped together in appropriate sizes to simulate ballast particles. Fouled ballast with a various void contaminant index (VCI) ranging from 20 to 70% VCI was modeled by injecting a specified number of miniature spherical particles into the voids of fresh ballast. The DEM simulation captures the behavior of fresh and fouled ballast as observed in the laboratory, showing that the peak shear stress of the ballast assembly decreases and the dilation of fouled ballast increases with an increasing VCI. Furthermore, the DEM also provides insight to the distribution of contact force chains and particle displacement vectors, which cannot be determined experimentally. These micromechanical observations clearly justify the formation of a shear band and the evolution of volumetric changes during shearing. The reduced maximum contact force associated with increased particle contact area due to fouling explains the decreased breakage of fouled ballast. An acceptable agreement was found between the DEM model predictions and laboratory data.

A method is proposed to determine the ultimate bearing capacity of a strip footing placed over granular and cohesive-frictional soils that are reinforced with horizontal layers of reinforcements. The reinforcement sheet is assumed to resist axial tension but not bending moment. The analysis was performed by using the lower bound theorem of the limit analysis in combination with finite elements. A single layer and a group of two layers of reinforcements were considered. The efficiency factors ${\eta }_{\gamma }$ and ${\eta }_c$ that need to be multiplied with the respective bearing capacity factor $N_{\gamma }$ and $N_c$ to account for the inclusion of the reinforcements were established. The results were obtained for different values of the soil internal friction angle ($\varphi$). The critical positions of the reinforcements, which would result in a maximum increase in the bearing capacity, were established. The required tensile strength of the reinforcement to avoid its breakage during the loading of the foundation was also computed. The results from the analysis were compared with those available in the literature.

This paper presents the consolidation and swelling characteristics of fly ash–montmorillonite clay mixes. Nine types of fly ash samples collected from different thermal power plants of the Eastern part of India have been used in this study. The amount of montmorillonite clay added to each fly ash sample is 10, 20, 30, 40, and 50%. The compression index ($c_c$) of the fly ashes indicates that the rate of consolidation is very fast. With an increase in montmorillonite clay content from 0.0 to 50%, the compressibility of the fly ash–montmorillonite clay mix increases, irrespective of the type of fly ash. The value of the compression index ($c_c$) of montmorillonite clay indicates that the embankments and fills made of fly ash–montmorillonite clay mixtures (i.e., 30, 40, and 50% of montmorillonite clay in the mix) and the structures constructed on such fills would suffer large deformation, whereas fly ash and fly ash mixed with 20% montmorillonite clay would not suffer large deformation. Specimens used for consolidation tests were compacted at the optimum moisture content (OMC) and the maximum dry density (MDD) obtained from standard Proctor compaction tests. Fly ash samples are nonswelling in nature, and the free swell index increases as the percentage of montmorillonite clay increases in the mixtures. Effects of the type of fly ashes, montmorillonite clay content in the mixes, permeability, and plasticity of fly ash–montmorillonite clay mixtures on compressibility of fly ash alone or in combination with montmorollonite clay mixes have been discussed herein. The effect of the percentage of montmorillonite clay and the plasticity index on the free swell index has also been highlighted.

In this paper, numerical limit analysis and semianalytical rigid block techniques are used to investigate the effect of the tunnel spacing on the stability of two circular tunnels excavated side by side. The tunnels are modeled under plane-strain conditions, which implies that they are assumed to be infinitely long. Bounds on the stability of the tunnels are obtained using finite-element limit analysis, the numerical formulation of which is based on the upper and lower bounds theorems of classical plasticity. Solutions are obtained using advanced conic programming schemes to solve the resulting optimization problems, and upper and lower bound estimates on the stability of the tunnels are obtained for a range of geometries. These bounds, which bracket the true collapse load from above and below, are found to differ by at most 5% for the cases where the solution does not approach zero. Results from this study are summarized in stability charts for use by practitioners.

Experimental and numerical studies have been conducted to investigate the earth pressure distribution on cylindrical shafts in soft ground. A small-scale laboratory setup that involves a mechanically adjustable lining installed in granular material under an axisymmetric condition is first described. The earth pressure acting on the shaft and the surface displacements are measured for different induced wall movements. Numerical modeling is then performed using the discrete element method to allow for the simulation of a large soil displacement and particle rearrangement near the shaft wall. The experimental and numerical results are summarized and compared against previously published theoretical solutions. The shaft-soil interaction is discussed, and conclusions regarding soil failure and the earth pressure distributions in both the radial and circumferential directions are presented.

A proper load transfer model describing the pile and surrounding soil interaction is important for accurately predicting the behavior of piles. In this paper, a new load transfer hyperbolic model for the pile-soil interface is developed based on soil-structure interface tests reported in the literature, which consider the characteristics of increasing initial shear stiffness, the development of shear strength at the pile-soil interface, the loading, step by step loading, unloading, and reverse loading shearing behavior of the pile-soil interface with consolidation. The proposed model was validated by the close agreement between the computed results and published case histories. Further studies based on the proposed model considering negative skin friction on single piles under pile head load and/or surcharge were subsequently conducted. It was found that the pile-soil interface undergoes complicated shearing, and the depth of the neutral plane (NP) and the skin friction along the pile shaft vary during consolidation. The magnitude of the pile head load and pile installation time has a significant impact on the depth of the NP and the dragload. Pile capacity was shown to decrease with consolidation.

An interface between compacted soil and a structure is commonly encountered in various geotechnical engineering projects, e.g., soil nails, retaining walls, shallow foundations, pile foundations, and so on. The interface strength depends on the way the soil-structure interface is formed. A cast-in-situ interface is very common in many geotechnical projects. This kind of interface is formed by placing concrete/cement grout over the prepared soil surface. The cement part can be formed over a prepared soil surface in two ways: (1) by normal gravity grouting and (2) by pressure grouting. In this study, a series of interface direct-shear tests was performed between compacted, completely decomposed granite (CDG) soil and cement grout under saturated conditions with different grouting pressures and normal stresses. The behaviors of the shear-stress–displacement curves of the soil-cement interface are similar to those of CDG soil. Grouting pressure and normal stress have influence on the behavior of the soil-cement interface. The failure envelopes for different grouting pressures are observed to be linear. The apparent effective interface friction angles are constant for different grouting pressures. On the other hand, apparent effective adhesion intercepts increase with grouting pressure. When the shear plane is fixed, the apparent effective interface friction angles for different grouting pressures are greater than the effective friction angle of CDG soil under the same normal stresses, which implies that a compacted CDG soil–cement grout interface behaves as a rough interface. The variation in interface shear strength with grouting pressure (grouting-pressure envelope) at the same shear-plane level is approximately linear, and declivities are constant for different normal stresses. A model is proposed for interface shear strength under saturated conditions that considers grouting pressure as an independent variable. The predicted interface shear strength of the proposed model agrees fairly well with the experimental data.

The study of the mechanical behavior of discontinuous rock masses is a rapidly growing subject. Much research has been reported in the literature concerning the estimation of the tunnel support pressures incorporating the real behavior of a rock mass using different types of constitutive models and rock parameters. These studies have favored the introduction of various analytical solutions for the easier geomechanical cases but have not been converted into numerical models suited for commercially available software and therefore could not be used in real and more complex engineering applications. The notable constitutive models used in common practice in rock mechanics are the Mohr-Coulomb and Hoek-Brown failure criteria. Most of the commonly available software supports only these two failure criteria. The difficulties faced in possibly implementing a new constitutive model into the numerical suites already available are so large that the studies using innovative constitutive models result in a mere academic exercise. In this paper, a new methodology is described for the application of the polyaxial constitutive model, which is characterized by the direct influence of all the principal stresses in the resistance of a rock mass. The methodology applied in this research uses the format of the Mohr-Coulomb model using the equivalent angle of friction and cohesion of the rock mass surrounding the tunnel. The equivalent parameters of rock mass resistance, which are directly derived from the common Mohr-Coulomb parameters, are also influenced by the intermediate principal stress ${\sigma }_2$, in accordance with what was suggested in the polyaxial strength criterion, and by the approach chosen for quantifying the uniaxial compressive strength ${\sigma }_{\text{cr}}$ of the rock mass. To demonstrate the practical applicability of this constitutive model, it has been used to predict the squeezing of rock observed and measured at three different instrumented sections of a tunnel.

For soil-structure interaction (SSI) problems, accurate modeling of the unbounded domain is an important issue. This paper deals with the three-dimensional seismic SSI analysis based on the substructure method by coupling the FEM and the scaled boundary FEM (SBFEM) approaches. The entire analysis is performed in the time domain making the proposed approach capable of dealing with nonlinearity of soil. To verify the developed program, the results from the present analysis are compared with those available in the literature. This verification has been performed for both externally applied dynamic load and seismic load. The effect of boundary conditions on the SSI response is evaluated. The numerical study performed indicates that the SBFEM can act as a computationally efficient boundary when compared with the conventional viscous dashpots. Next, application of the FEM-SBFEM for SSI problems is demonstrated. A dam-foundation interaction analysis is carried out, and the effect of the inhomogeneity of the foundation soil on the dynamic response of the structure is evaluated. In addition, seismic SSI analysis of a building is carried out for a real earthquake excitation. The effects of the dynamic characteristics of soil and structure on the dynamic SSI response are analyzed.

Mechanically stabilized earth (MSE) walls offer simple construction techniques, pleasing aesthetics, and cost-effective solutions as an alternative to conventional gravity walls. However, design and construction should be carefully evaluated to achieve satisfactory performance of the wall. A case study is presented on a MSE wall located on State Highway 342 in Lancaster, Texas. The horizontal movement of the MSE wall was between 300 and 450 mm within 5 years of construction. A forensic investigation was performed to determine the causes of the excessive movement. It was identified that inadequate reinforcement length was one of the contributing factors that caused horizontal displacement of the MSE wall. The objective of this study was to determine the effects of soil reinforcement on excessive movement of the MSE wall. As a part of the forensic investigation, two inclinometers were installed at the site to monitor any additional movement of the MSE wall. The inclinometer results suggested that the wall continued to move at an average rate of $4.5\hspace{0.17em}\text{mm/month}$ during the investigation period. A finite-element (FE) program was used to simulate horizontal displacement and stability of the MSE wall. It was observed that the numerical modeling results were in good agreement with inclinometer results. A parametric study was conducted to identify the effects of soil reinforcement on horizontal movement at varied wall heights and backfill conditions. Numerical analyses results indicated that the effect of reinforcement stiffness was not significant at a wall height of 4 m compared with 8 and 12 m. The wall movement varied from 74 to 29 mm for an increase in reinforcement stiffness from $250\hspace{0.17em}\text{to}\hspace{0.17em}\mathrm{42,000}\hspace{0.17em}\text{kN/m}$ at $1.0H$ reinforcement length. The variations in displacement with reinforcement lengths suggested that substantial reduction in displacement occurred for an increase in length-height ($L/H$) ratio from 0.5 to 0.7. FE modeling results were used for sensitivity analysis employing a statistical analysis program. Based on the analyses, reinforcement length and stiffness were identified as influential factors for the horizontal displacement of MSE walls at a specific height.

Carbonate soils have some distinctive features such as compressibility and skeletal particle crushability that make them distinguishable from other types of soils. Many experimental models have been developed to describe the complex behavior of carbonate soils, but despite these numerous works, there is no unified approach that can model the behavior of various types of these soils. In this paper, a new approach based on artificial neural networks is presented to predict the mechanical behavior of different carbonate soils. The network had five input neurons, namely, relative density, axial strain, maximum void ratio, calcium carbonate content, and confining pressure; ten neurons in the hidden layer; and two neurons in the output layer, namely, deviatoric stress and volumetric strain at the end of each increment. The network was trained and tested using a database that included results from a comprehensive set of triaxial tests on three carbonate soils. Comparison of the model prediction and experimental results revealed that the proposed approach was accurate and trustworthy in representing the mechanical behavior of various carbonate soils.

Trench stability is a conventional geotechnical problem; however, current evaluations are often based entirely on empiricism. This paper uses numerical finite-element upper and lower bound limit analysis to produce stability charts for two-dimensional and three-dimensional homogeneous and inhomogeneous undrained diaphragm wall trenches. Using the limit theorems cannot only provide a simple and useful way of analyzing the stability of the trench, but also avoid the shortcomings and arbitrary assumptions underpinning the limit equilibrium method. By considering the effects from the bentonite slurry pressures, the collapse load in this study has been bracketed to within $\text{±}8.5\%$ or better by the numerical upper and lower bound limit analyses. The chart solutions can be used to predict either the critical depth or the safety factor of the trench and provide a convenient tool for preliminary designs by practicing engineers.