A review of techniques, advances and outstanding issues in numerical modelling for rock mechanics and rock engineering

Numerical methods in rock mechanics

The effect of scale on the shear behaviour of joints is studied by performing direct shear tests on different sized replicas cast from various natural joint surfaces. The result show significant scale effects on both the shear strength and deformation characteristics. Scale effects are more pronounced in the case of rough, undulating joint types, whereas they are virtually absent for planar joints. The key factor is the involvement of different asperity sizes in controlling the peak behaviour of different lengths of joints. It is shown that as a results both the joint roughness coefficient (JRC) and the joint compression strength (JCS) reduce with increasing scale. The behaviour of multiple jointed masses with different joint spacing is also considered. It is found that despite unchanged roughness, jointed masses consisting of many small blocks have higher peak shear strength than jointed masses with larger joint spacing. These scale effects are related to the changing stiffness of a rock mass as the block size or joint spacing increases or decreases. Economic methods for obtaining scale-free estimates of shear strength are described.

Experimental studies of scale effects on the shear behaviour of rock joints

Biocementation is a recently developed new branch in geotechnical engineering that deals with the application of microbiological activity to improve the engineering properties of soils. One of the most commonly adopted processes to achieve soil biocementation is through microbially induced calcite precipitation (MICP). This technique utilizes the metabolic pathways of bacteria to form calcite (CaCO3) that binds the soil particles together, leading to increased soil strength and stiffness. This paper presents a review of the use of MICP for soil improvement and discusses the treatment process including the primary components involved and major affecting factors. Envisioned applications, potential advantages and limitations of MICP for soil improvement are also presented and discussed. Finally, the primary challenges that lay ahead for the future research (i.e. treatment optimization, upscaling for in situ implementation and self-healing of biotreated soils) are briefly discussed.

State-of-the-Art Review of Biocementation by Microbially Induced Calcite Precipitation (MICP) for Soil Stabilization

Modified Mohr–Coulomb criterion for non-linear triaxial and polyaxial strength of jointed rocks

Laboratory model studies on unreinforced and geogrid-reinforced sand bed over stone column-improved soft clay

Blast induced rock mass damage around tunnels

Rocks encountered at many underground construction sites are laminated and exhibit direction-dependent strength behavior. It is also a well-established fact that the strength varies in a nonlinear manner with confining pressure. There is a need of strength criterion which could capture the nonlinearity as well as the anisotropy in the triaxial strength behavior of the rocks. It is essential that the criterion should be simple and must involve minimum testing to the extent possible. Further, the parameters of the criterion should have wide acceptability among the geotechnical fraternity. In the present study, a nonlinear strength criterion for transversely isotropic rocks is presented. Critical state concept Barton (Int J Rock Mech Mining Sci Geomech Abstr 13(9):255–279, 1976) has been used to define the curvature of the criterion. With a correctly defined curvature and starting from a reference point (UCS), it is possible to accurately assess the triaxial strength for given confining pressure. An experimental study conducted on triaxial strength behavior of three types of anisotropic rocks namely phyllite, slate and orthoquartzite has been discussed. A data base comprising more than 1140 triaxial tests conducted worldwide on anisotropic rocks has been compiled. Statistical evaluation of goodness of fit of the proposed criterion to the data base has been carried out. Further, the predictive capabilities of the proposed criterion have been evaluated by determining the error in estimation of triaxial strength if only few triaxial test data are available for determining the criterion parameters. The data base has also been back analyzed to assess the critical confining pressure for anisotropic rocks. Statistically, the critical confining pressure for anisotropic rocks can be taken nearly equal to 1.25 times the maximum UCS (obtained by applying load either parallel or perpendicular to planes of anisotropy). It is concluded that reasonable estimates of the triaxial strength of anisotropic rock can be made through the proposed criterion using minimum amount of triaxial test data available.

A nonlinear criterion for triaxial strength of inherently anisotropic rocks

Rock mass strength parameters mobilised in tunnels

Stability analyses of slopes are routinely done to identify potential landslide sections. This is done for applying proper mitigation techniques. The stability of slopes is generally defined by using the term factor of safety (FOS). Various analytical and numerical models for calculating the value of FOS of slopes have been given by researchers. They had identified various independent parameters affecting the stability of slopes. The relation between FOS and influencing parameters is non-linear, which makes it a complex, multivariate problem. Recently intelligent systems have gained acknowledgement in solving such highly complex, multivariate problem. Artificial neural network (ANN), have got high degree success in solving such problem. However, ANN has its own limitations. Various researchers identified slow learning rate and getting trapped in local minima as the potential shortcoming of ANN. These shortcomings are associated with optimisation algorithm in the ANN. A number of metaheuristic optimisation...

Narendra Kumar Samadhiya

Papers

Laboratory model studies on unreinforced and geogrid-reinforced sand bed over stone column-improved soft clay

Blast induced rock mass damage around tunnels

A nonlinear criterion for triaxial strength of inherently anisotropic rocks

Rock mass strength parameters mobilised in tunnels

A PSO-ANN hybrid model for predicting factor of safety of slope