Computers and Geotechnics 

About: Computers and Geotechnics is an academic journal published by Elsevier BV. The journal publishes majorly in the area(s): Finite element method & Geotechnical engineering. It has an ISSN identifier of 0266-352X. Over the lifetime, 4708 publications have been published receiving 126623 citations.

Two-dimensional slope stability analysis by limit equilibrium and strength reduction methods

Abstract: In this paper, the factors of safety and the locations of critical failure surfaces obtained by the limit equilibrium method and strength reduction method are compared for various slopes. For simple homogenous soil slopes, it is found that the results from these two methods are generally in good agreement except when ϕ′ is zero. It is also found that the strength reduction method (SRM) is usually not sensitive to the dilation angle, soil moduli or the solution domain size and the choice of these parameters is not critical in the analysis. While the SRM may perform well in many cases, two major limitations of this method are found in this study: it is sensitive to the nonlinear solution algorithm for the case of a soft band with frictional material and it is incapable of determining other failure surfaces which may be only slightly less critical than the SRM solution but still require treatment for good engineering practice.

A novel discrete model for granular material incorporating rolling resistance

Abstract: This paper presents a novel two-dimensional (2D) discrete model for granular materials with rolling resistance. The salient features of our formulation are: it consists of a geometrically derived kinematical model, physically based mechanical contact models and locally equilibrated equations governing the motion of the rigid particles; only one additional parameter δ needs to be introduced in the model when compared with the standard discrete element method (DEM). In the study, precise definitions of pure sliding and pure rolling were proposed, and a decomposition of a general contact displacement was given in terms of these rolling and sliding components which are then linked to energy dissipation. The standard DEM assumption that grains are in contact at discrete points was here replaced by the assumption that grains are in contact over a width. By making the idealization that the grain contact width is continuously distributed with normal/tangential basic elements, we established a rolling contact model together with normal/tangential contact models, and also related the governing equations to local equilibrium. As an example of its application, the present model was incorporated into a DEM code to study the angle of internal friction ϕ of the material. Fifty-four DEM simulations showed that ϕ predicted by the novel model was increased in comparison to the standard DEM prediction, and may be closer to the values observed experimentally provided that the δ – ϕ relationship established in this paper was used.

A numerical investigation of the stability of unsaturated soil slopes subjected to transient seepage

Abstract: Slope instability in unsaturated residual soils and loose fills has attracted increasing attention in recent years around the world such as Brazil, South Africa, Japan and in the Far East. Rain-induced failures are the most common ones. Rainfall leads to the development of perched water table, rising the main groundwater level and soil erosion (due to concentrated water flow), resulting in an increase in pore water pressure or a reduction in soil matric suction. This, in turn, results in a decrease in shear strength on the potential failure surface to a point where equilibrium can no longer be sustained in the slope and then failures occur. However, the present understanding of the influence of transient seepage in unsaturated soils, due to water infiltration under various boundary and ground conditions, and hydrogeological regimes on slope stability is still relatively poor compared with other elements of geomechanics. To investigate the influence of various rainfall events and initial ground conditions on transient seepage and hence slope stability, a parametric study has been conducted using the finite element method. A typical steep unsaturated cut slope in Hong Kong has been adopted for the parametric study. Variables considered in the parametric study include isotropic and anisotropic soil permeability, initial water table at upslope boundary, rainfall intensity and duration. Pore water pressures or suctions predicted during the transient seepage analyses are then used as input ground water conditions for subsequent limit equilibrium analyses of the stability of the slope. Factor of safety is calculated using Bishop’s simplified method, with modified Mohr–Coulomb failure criterion to allow for shear strength variation due to the presence of matric suction. Infiltration due to rain water causes a reduction of matrix suction, but an increase in moisture content and soil permeability in unsaturated soils. Perched water table is developed above the main water table. The factor of safety is not only governed by the intensity of rainfall, initial ground water table and the anisotropic permeability ratio, but it also depends on antecedent rainfall duration. A critical rainfall duration can be identified, at which the factor of safety is the lowest.

The signature of shear-induced anisotropy in granular media

Abstract: This paper presents a micro-mechanical study on the characteristics of shear-induced anisotropy in granular media. Based on three-dimensional Discrete Element Method (DEM) simulations, the distinct features associated with the evolution of internal granular structure and different anisotropy sources during drained/undrained shearing of granular samples are carefully examined. The study finds that static liquefaction occurs when the geometrical anisotropy in a sample dominates the mechanical anisotropy in the overall shear strength, and the weak force network features an exceptionally high proportion of sliding contacts and develops certain degree of anisotropy. Phase transformation corresponds to a transitional, unstable state associated with a dramatic change in both coordination number and the proportion of sliding contacts in all contacts. The critical state in a granular material is always associated with a highly anisotropic fabric structure wherein both the critical void ratio and critical fabric anisotropy are uniquely related to the mean effective stress. The relations provide a more comprehensive definition for the critical state in granular media with proper reference to the critical fabric anisotropy.

The use of discrete fracture networks for modelling coupled geomechanical and hydrological behaviour of fractured rocks

Abstract: We present a discussion of the state-of-the-art on the use of discrete fracture networks (DFNs) for modelling geometrical characteristics, geomechanical evolution and hydromechanical (HM) behaviour of natural fracture networks in rock. The DFN models considered include those based on geological mapping, stochastic generation and geomechanical simulation. Different types of continuum, discontinuum and hybrid geomechanical models that integrate DFN information are summarised. Numerical studies aiming at investigating geomechanical effects on fluid flow in DFNs are reviewed. The paper finally provides recommendations for advancing the modelling of coupled HM processes in fractured rocks through more physically-based DFN generation and geomechanical simulation.