International Journal of Geomechanics

Nonlinearity and anisotropy of stress-strain responses are important factors influencing the behavior of soil. To describe this complex behavior of soils, a hypoelastic constitutive model is developed based on cross-anisotropic elasticity, which involves four parameters: the bulk modulus, tangent Young’s modulus, coefficient of volume deformation, and Poisson’s ratio. To satisfactorily predict the stiffness of soils at various strain levels, especially in small strain regions, a new stress-strain fitting relationship with four parameters is proposed. For normally consolidated or weakly overconsolidated clay, the dilatancy equation of the Cam-clay model is used to determine the coefficient of volume deformation. Overall, the model is convenient to use. Ten material parameters are involved, which can be obtained from an isotropic compression test, a set of drained triaxial compression tests, and a uniaxial compression test. The computed results of the model are in good agreement with the data from the tests, in which each specimen was reconsolidated under the $k_0$ condition. The results verify the rationality of the model.

This paper investigates the effect of reinforcement and nonhomogeneity on the propagation of cracks caused by horizontally polarized shear waves in a heterogeneous fiber-reinforced medium. The effects of reinforcement and heterogeneity on the propagation of the crack are highlighted in this study. The stress intensity factor at the crack tip for a concentrated force of a constant intensity has been calculated and depicted by means of graphs for various cases. It is observed that fiber reinforcement and heterogeneity parameters decrease the stress intensity factor. Remarkably, the stress intensity factor decreases with the increase in the length and speed of the crack. Also, a comparative study was made for the stress intensity factor in reinforced medium over reinforced-free medium and heterogeneous medium over the homogeneous medium. Moreover, some important peculiarities were observed in graphs.

Using a microscopic modeling approach, a simplification of the discrete element’s shape was done by using irregular convex polyhedrons to reproduce the geometry-dependent behavior of rockfills. Numerical modeling of the triaxial compression tests was conducted using a combined FEM and discrete-element method (FEM/DEM). The micromechanical properties of the numerical sample were calibrated to match the macroscopic response of the real material. The numerical results quantitatively agree with the laboratory results, which reproduce typical features of the mechanical behavior of rockfills, such as nonlinear stress-strain relationship, compaction, and shear dilatancy. The combined FEM/DEM simulation provides an opportunity for a quantitative study of the microstructure of particle assemblages, which give a better understanding of the mechanical characteristics of rockfills.

Soil shear can be described as a dynamical system in which particles move at random shear strains into the steady-state flow structure in a process governed by simple friction. This paper studies strain-rate effects in soil shear in the context of dynamical systems soil-shear theory. The theory highlights the fact that conditions at the start of plastic deformation are strain-rate dependent and that much of the initial linear variation of stresses with strain is not attributable to the elasticity behavior of the soil but rather is the expected small-strain behavior of a nonlinear process of plastic deformation. The static coefficient of friction dominates at very small strains, after which the friction coefficient reduces to its dynamic value. Variations with strain rate in the stress-strain and void ratio–strain curves are small because of the correspondingly small dependence of the friction coefficients on strain rate.

In this study, the accuracy of a fully nonlinear method against an equivalent linear method for dynamic analysis of soil-structure interaction is investigated comparing the predicted results of both numerical procedures. Three structural models, including 5-story, 10-story, and 15-story buildings, are simulated in conjunction with two soil types with shear-wave velocities less than $600\hspace{0.17em}\text{m}/\text{s}$. The aforementioned frames were analyzed under three different conditions: (1) fixed-base model performing conventional time history dynamic analysis under the influence of earthquake records, (2) flexible-base model (considering full soil-structure interaction) conducting equivalent linear dynamic analysis of soil-structure interaction under seismic loads, and (3) flexible-base model performing fully nonlinear dynamic analysis of soil-structure interaction under the influence of earthquake records. The results of these three cases in terms of average lateral story deflections and interstory drifts are determined, compared, and discussed. It is concluded that the equivalent linear method of the dynamic analysis underestimates the inelastic seismic response of midrise moment resisting building frames resting on soft soils in comparison with the fully nonlinear dynamic analysis method. Therefore, a design procedure using the equivalent linear method cannot adequately guarantee the structural safety for midrise building frames resting on soft soils.

Reliable and economical design of portland cement concrete (PCC) pavement structural systems relies on various factors, among which is the proper characterization of the expected permeability response of the concrete mixes. Permeability is a highly important factor that strongly relates the durability of concrete structures and pavement systems to changing environmental conditions. One of the most common environmental attacks that causes the deterioration of concrete structures is the corrosion of reinforcing steel due to chloride penetration. On an annual basis, corrosion-related structural repairs typically cost millions of dollars. To properly characterize the permeability response of a PCC pavement structure, the Kansas DOT (KDOT) generally runs the rapid chloride permeability test (RCPT) to determine the resistance of concrete to penetration of chloride ions. RCPT typically measures the number of coulombs passing through a concrete sample over a period of 6 h at a concrete age of 7, 28, and 56 days. In this study, back-propagation artificial neural network (ANN) and regression-based permeability response prediction models for rapid chloride penetration test were developed by using the database provided by KDOT to reduce the duration of the testing period or ultimately eliminate the need to conduct the RCPT. The back-propagation ANN learning technique proved to be an efficient methodology to produce relatively accurate permeability response-prediction models. Comparison of the prediction accuracy of the developed models proved that ANN models have outperformed their counterpart regression-based models. The sensitivity analysis also was performed on randomly selected data sets to evaluate the reliability of developed models. The developed ANN models proved effective in characterizing the permeability (RCPT results) response of concrete mixes used in PCC pavements.

Considering the interaction mechanisms between a subway tunnel’s structure and the surrounding soil, a new theoretical method was established to analyze the vibration characteristics of the tunnel structure. The tunnel structure is assumed to be a moderately thick cylindrical shell that was never previously used, and all following researches were done on this basis. To begin, the vibration equation of the tunnel structure was established based on the moderately thick cylindrical shells theory, which takes into account transverse shear deformation. Then, a motion equation was set up for the soil around the tunnel in the framework of Navier’s wave theory, applicable to a homogeneous, isotropic, linear elastic medium. Based on said analysis and combined with a wave-propagation approach, the vibration control equation of the tunnel structure was established by considering soil-structure dynamic interaction according to the interface conditions. Using the dispersion characteristic equation, the vibration characteristics of the tunnel structure were analyzed. Through the comparison of the analytical results with those obtained based on thin shell theory or the FEM, the effectiveness of this research was verified. Finally, the influences of tunnel radius, wall thickness, and length on the vibration characteristics of tunnel structure were analyzed. Some important findings are drawn as follows: (1) The natural frequencies of each order, calculated using the method proposed in this paper, are close to the solutions based on FEM, and the relative error is less than 10%; (2) The natural frequencies of the tunnel structure that were calculated based on this theory are lower than those based on the thin shell theory; (3) Additional stiffness is the main influencing factor of the soil medium on the vibration characteristics of tunnel structure; (4) When the lower order is dominating in one-modal analysis, it would produce a larger error if soil-structure interaction is ignored; and (5) The natural frequency of tunnel structure decreases with the increase of tunnel radius, wall thickness, and length.

Strength anisotropy should be introduced into stability analyses, because the shear direction differs at each sliding point. However, few experiments evaluating the effects of anisotropic consolidation on undrained shear strength have been available for practical construction problems. Therefore, torsional shear tests were conducted on specimens consolidated and swollen in different directions to evaluate the anisotropy of undrained shear strength. Furthermore, to treat two-dimensional problems, the tests were also performed under the plane strain condition, where no radial strain occurs. Results show that the anisotropy of the undrained shear strength is closely related to the differences between consolidation and shearing in terms of directions and stress conditions. Finally, slope stability analyses were conducted to demonstrate how the anisotropy of the undrained shear strength obtained from the experiments can be practically used in field analyses.

Torsional loads on pile foundations are induced by the action of eccentric horizontal forces on the supporting structures. Such loading not only initiates twisting at the pile head but also reduces its axial capacity significantly with increased settlement of the foundation. Several theoretical and experimental investigations have already been carried out on piles under torsional load, as evidenced by the available literature on the subject, although contributions on the influence of combined torsional and axial loads on pile foundations are rather limited. This paper presents a novel numerical model (boundary-element method) to analyze the response of a single vertical floating pile subjected to simultaneous torsional and axial loads. The nonlinear stress-strain response of soil has been incorporated in the model by means of the hyperbolic model, whereas the pile material has been idealized as elastic–perfectly plastic. The effect of progressive pile-soil slippage at the interface is considered. Apart from predicting the load-displacement response and incremental angle of twist of piles under combined torsional and axial loading, the shear-stress profiles and the effect of vertical loads on the torsional capacity of the piles are some of the salient features captured by the proposed model. Validation of the proposed model by means of a comparison with existing models and experimental data indicates the suitability and accuracy of the solutions developed. The proposed model is also applied successfully to selected case studies on piles in clay, sand, and layered soil, and important conclusions are drawn.

Limit equilibrium models of forces that act on joints in rock masses have a disadvantage in that it is impossible to explicitly integrate joint roughness amplitude because the models consider only the nondimensional parameters related to asperity geometry. However, for adequate joint roughness characterization, it is essential to consider amplitude as well. Thus, the formulation of a limit equilibrium model of the strain energies associated with rock joints is proposed, in which two different joints may yield under the same shear stress while they have asperities with the same slope but different amplitudes, because they actually have different strengths.

In this paper, a simplified assessment method for the wave-induced liquefied depth in a shallow seabed is proposed. By introducing a weighting factor, both the oscillatory and residual pore pressures were considered in the liquefaction criteria. Normalized charts were presented for a quick and simple evaluation of the maximum liquefied depth as a function of wave and soil parameters. Finally, parametric analyses were performed to clarify the applicable range of this criterion. It is found that the increases of relative density and consolidation coefficient will obviously enhance the influence of the oscillatory pore pressure on the liquefaction of a shallow seabed, as well as reduce the liquefaction potential.