International Journal of Geomechanics

To study the deformation property of large-thickness self-weight collapsible loess and to understand the moisture migration law and matrix suction characteristics, a 40-m-diameter soaking test was conducted in the field with self-weight collapsible loess at a thickness of 36.5 m. The results showed that (1) the field collapse deformation law of the large-thickness self-weight collapsible loess varied in two periods, namely, the soaking period and the water cutoff period; (2) during the soaking test, the distribution of crack patterns appeared from local to overall, from near to far, and from dense to sparse, then gradually extended; (3) the volumetric moisture content changed in different soil locations; (4) suction developed steadily before soaking, whereas with a large amount of water, suction dropped steeply within a short time; and (5) the water content of soil above 20 to 25 m increased rapidly and soon reached saturation, whereas the water content of soil below that depth increased slowly and reached saturation with difficulty. The test results may be useful for similar projects in the area of self-weight collapsible loess with large thickness, and to help revise Chinese codes for building construction in collapsible loess regions.

The slip line method has been extended to consider the tangential stress and arbitrary magnitude of wall movement. An analytical solution has also been proposed for the arbitrary mode of wall movement, and the soil mass behind the wall can be homogeneous or layered. The mobilized internal friction angle of the soil and the soil-wall interface friction angle change with the movement of the wall; this has been widely accepted. However, the development of them is not simultaneous. The mobilized friction angles are used in the slip line method and the simplified slip line method to yield the nonlimit lateral earth pressure. Results indicate that earth pressure decreases exponentially with increasing wall movement. Comparisons of the calculated results with measured data and FEM results show that the present analytical method can provide good prediction of the lateral earth pressures and the limit wall movement equal to $0.3\%H$ is appropriate in the calculation (where $H$ is the excavation depth).

Lower-bound calculations based on the FEM are used to determine the bearing capacity of a strip foundation subjected to an inclined, eccentric load on cohesionless soil with varying surcharges and with friction angles of 25, 30, and 35°. The soil is assumed to be perfectly plastic following the Mohr-Coulomb failure criterion. The results are reported as graphs showing the bearing capacity as a function of the friction angle, eccentricity, inclination, and surcharge. These results have been compared, and for smaller eccentricities, except in the case of no surcharge, the lower-bound values are the greater, the discrepancy increasing with growing surcharge. Positive load inclinations have a negative effect for smaller eccentricities but may have a beneficial effect on the bearing capacity for greater eccentricities. Negative load inclinations have the opposite effect, and especially for small friction angles and great surcharges, other values are considerably greater than the lower-bound values.

An effective strategy in reducing train-induced vibrations on neighboring structures is to use open trenches on both sides of the railway lines. This paper investigates the effect of the trench’s shape on its performance. For this purpose, a V-shaped trench was first modeled using finite-element code, and its efficiency was confirmed in reducing the induced vibrations caused by passing the MD36 passenger bogie in comparison with a rectangular-shaped trench. In this regard, results indicate that the maximum values of the amplitude reduction ratio ($A_r$) for the ground displacement before the V-shaped trench for train speeds of $80\hspace{0.17em}\text{and}\hspace{0.17em}120\hspace{0.17em}\text{km}/\text{h}$ were 1.17 and 1.28, respectively, which were less than the value of 2 obtained for the rectangular trench. In the final stage, an optimization algorithm was used to present the procedure of calculating optimized shape of the proposed V-shaped trench for various train speeds.

In this paper, the feasibility of developing and using artificial neural networks (ANNs) for modeling the monotonic behaviors of various angular and rounded rockfill materials is investigated. The database used for development of the ANN models is comprised of a series of 82 large-scale, drained triaxial tests. The deviator stress-volumetric strain versus axial strain behaviors were first simulated by using ANNs. A feedback model using multilayer perceptrons for predicting drained behavior of rockfill materials was developed in the MATLAB environment, and the optimal ANN architecture was obtained by a trial-and-error approach in accordance with error indexes and real data. Reasonable agreement between the simulated behaviors and the test results was observed, indicating that the ANNs are capable of capturing the behavior of rockfill materials. The ability of ANNs to predict the constitutive hardening-soil model parameters, residual deviator stresses, and corresponding volumetric strain was also investigated. Moreover, the generalization capability of ANNs was also used to check the effects of items not tested, such as dry density, grain-size distributions, and Los Angeles abrasion.

Underground backfill plays an important role in the mining industry, and is one of the key elements in the routine operation of many underground mines. Its main role is to improve ground stability and reduce ore dilution. Its other advantages include the reduction of surface mining waste disposal, which in turn reduces and even eliminates some problems, such as tailing dam failure or acid mine drainage (AMD), associated with mining waste management. To ensure a safe and economical backfill design, the strength of the backfill must be high enough to allow it to remain stable during the exploitation of adjacent stopes, at the very least. This minimum required strength is usually estimated using a solution proposed in the early 1980s. However, this solution includes several limitations, including the following: it assumed a zero friction angle of backfill; it neglected the surcharge on top of the exposed backfill; it assumed an equivalency between the backfill cohesion and the bond cohesion (adherence) along the interfaces between the backfill and side walls; it neglected the shear strength contributed by friction along the interfaces between the backfill and back and side walls, as well as the shear strength contributed by cohesion along the interface between the backfill and back wall; and it assumed a high aspect ratio (height-over-width) stope. Recently, a modified solution was proposed, using the same basic approach and many of the same assumptions. In this article, the original and modified solutions are first reviewed. Further modifications are given, leading to a generalized solution that overcomes the limitations involved in the original and modified solutions. The generalized solution is validated against experimental results available in the literature.

In the recent past, the topic of blast loads on structures has received considerable attention from researchers. Site-specific empirical models for blast-induced vibration parameters like peak particle velocity (PPV), peak pressure (PP), peak particle displacement (PPD), and pore pressure ratio (PPR) are commonly used for blast-resistant designs. However, these empirical models do not consider the variation in soil properties, e.g., the degree of saturation and uncertain in situ conditions. Hence, in this paper, a total of 120 pieces of blast data from various soil sites have been collected and used to propose a generalized empirical model for estimating blast-induced vibration parameters by considering three basic soil properties, namely, unit weight, degree of saturation, and Young’s modulus. Standard errors and coefficients of correlation for the prediction of blast-induced vibration parameters by various empirical models are obtained with respect to the observed soil field data. The present empirical model has been compared with the models of other researchers and found to be in good agreement for specific cases. The present model, having maximum coefficient of correlation and minimum standard error, can be directly used in the calculation of blast loading for design. The present model has also been validated for various degrees of saturation. It has been found that the present model predicts fairly for fully saturated soils irrespective of soil type, and predicts higher values (critical values for design) for partially saturated soils. In the absence of field blast vibration data because of economic, safety, and environmental constraints, the present model will evaluate the blast vibration parameters by using only three basic soil properties.

The influence of the flow rule on the bearing capacity of strip foundations placed on sand was investigated using a new kinematic approach of upper-bound limit analysis. The method of stress characteristics was first used to find the mechanism of the failure and to compute the stress field by using the Mohr-Coulomb yield criterion. Once the failure mechanism had been established, the kinematics of the plastic deformation was established, based on the requirements of the upper-bound limit theorem. Both associated and nonassociated plastic flows were considered, and the bearing capacity was obtained by equating the rate of external plastic work to the rate of the internal energy dissipation for both smooth and rough base foundations. The results obtained from the analysis were compared with those available from the literature.

Geomaterials behave differently under different types of loadings, such as compression, shear, or tension; they exhibit weaker response in tension. To increase the tensile and shear strengths of the soil, different methods of reinforcement, such as geosynthetics, have been used in earth structures such as retaining walls, earth dams, and slopes. The use of geosynthetics has attracted the attention of engineers and researchers in recent years. However, there are some significant problems associated with geosynthetics, such as low tensile strength, creep, and for some applications, a low stiffness modulus. In this research, a geocomposite (GC), made of carbon fiber–reinforced polymer (CFRP), is proposed and studied. The interface properties of the CFRP and backfill soil are investigated experimentally using a cyclic multidegree-of-freedom (CYMDOF) device. Then an elastic–plastic constitutive model, the hierarchical single surface (HISS), is used to characterize the behavior of the interface between the CFRP and backfill soil. The constitutive model is verified by predicting the laboratory behavior of interface for tests used to find parameters and comparing that to independent tests. Based on the investigation, CFRP can be considered to be appropriate and beneficial as reinforcement in earth structures, because it has relatively high friction angle, high tensile strength, high Young’s modulus, and high resistance to aggressive environment.

In the present analysis, a methodology is developed to calculate the pseudodynamic passive resistance on the back of a battered-faced retaining wall supporting cohesive-frictional backfill using the horizontal slice method and limit-equilibrium principle. The results are presented in both tabular and graphical nondimensional form. The analysis identifies a nonlinear rupture surface that depends on the wall-backfill parameters. The effects of wide variations in the parameters, such as the wall inclination angle ($\alpha$), wall friction angle ($\delta$), soil friction angle ($\mathrm{\Phi }$), shear-wave velocity ($V_s$), primary wave velocity ($V_p$), and horizontal and vertical seismic accelerations ($k_h$, $k_v$) on the seismic passive resistance coefficients have been studied.

In this study, a method is developed for predicting the future deformation of soft ground, based on measured data. Because it is difficult to predict the deformation behavior of soft ground on the basis of laboratory consolidation test results only, in situ observations are generally made. An inverse analysis is effective for identifying the in situ parameters of the ground and for predicting future deformation based on those parameters. In the method proposed, the induced anisotropy (transverse isotropy) of the ground is introduced to solve the problem of predicting lateral displacement, and a simplified hyperbolic model is introduced to simulate nonlinear shear behavior. Furthermore, the change in volume compressibility of the material and the decrease in permeability caused by consolidation are considered simultaneously through the use of a statistical model for the soil parameters. This statistical model, which takes the nonlinearity of the parameters into account, is called the stochastic nonlinear model (SNM). To verify the usefulness of the proposed method, the results of two-dimensional deformation tests are analyzed.

The elastic modulus ($E_j$) of a jointed rock mass is an important parameter for rock mechanics. This study examines the capability of Gaussian process regression (GPR) for determination of the $E_j$ of jointed rock masses. The GPR is a Bayesian nonparametric model. The joint frequency ($J_n$), joint inclination parameter ($n$), joint roughness parameter ($r$), confining pressure (${\sigma }_3$), and elastic modulus ($E_i$) of intact rock are considered as inputs of the GPR. The output of the GPR is the $E_j$ of jointed rock masses. The developed GPR has been compared with the artificial neural network (ANN) models. Variance of the predicted $E_j$ of jointed rock masses is obtained from the GPR. The results show that the developed GPR is a promising tool for the prediction of the $E_j$ of jointed rock masses.

The propagation of torsional surface waves in a transversely isotropic substratum lying over a dry sandy gibson half-space in the presence of initial stress (compressive and tensile) and gravity have been studied analytically and computed numerically. The dispersion equation has been derived in a closed form. The effect of various inhomogeneity parameters on the torsional wave propagation has been exhibited by means of graphs. The influence of initial stress (compressive and tensile), Biot’s gravity parameter, and the sandy parameter have also been shown on the phase velocity of the torsional surface wave. Dispersion equations are in perfect agreement with the standard results when derived for some particular cases. Graphical user interface software has been developed to generalize the effect of various parameter discussed.

A simple analytical method has been developed that characterizes plane shock wave propagation through reinforced soil and the dynamic interaction between soil and retaining wall panels. The shock wave attributable to an explosion in the backfill was modeled as a velocity boundary condition at a standoff distance from the wall. The exact solution to this problem was obtained using the Laplace transform method. Full-scale explosive test data from 4.6-m-high and 24-m-wide reinforced soil walls were used to validate the analytical methodology. The accuracy of the analytical method has further been verified by finite-element analysis. The method is adequate for the response analysis of mechanically stabilized embankment walls under ground shock attributable to an explosion in the backfill.

Modern methods for calculating slope stability in current finite-element programs involve the stepwise uniform reduction of the soil strength parameters. However, prediction of the strength-reduction law under the influence of external factors is not actually possible. The suggested method for safety-factor minimization will produce the most reliable estimation of slope stability. This idea is illustrated by calculating the safety factor for embankments composed of clay loam and sand.

Discrete element method (DEM) simulations are used for measuring the macroscale and microscale changes in stress and fabric for the cyclic loading of a two-dimensional granular assembly. The stress–strain–dilatancy tendencies are similar to those of sands. After repeated loading cycles, the fabric follows a steady-state circuit of evolution within each cycle, but reversals in the loading direction are always accompanied by abrupt changes in the fabric. A consistent and strong inverse relationship is found, however, between the average coordination number and an effective void ratio, defined by excluding particles that do not participate in supporting the applied stress. A strong and consistent correlation is also found between the deviator stress ratio and a trong fabric ratio throughout the cyclic loading.