Numerical Simulation of Direct Test for Rock
The shear behaviour of rock joint is a combination of complex phenomena such as normal dilation, asperity shearing or sliding, contact area undergoing shearing or sliding and stiffness of the surrounding rock mass. Hence, a constitutive model for joint behaviour has to consider a large number of assumptions and uncertainties. Considerable efforts have been made in the past by various researchers to explain the shear behaviour of rock joint. Based on their laboratory, analytical and numerical studies various shear strength models have been proposed by them. In the present study numerical modeling is done for simulating the experimental conditions. Numerical study is performed based on the Distinct Element Method (DEM) and using the Universal Distinct Element Code (UDEC) developed by ITASCA Consulting Group Inc. Direct shear test were carried out on numerically simulated rock joint using UDEC. The shear behavior of rock joint examined with asperity like 15-15 and 30-30 at different normal stress. The result of the laboratory shear test performed on the sample with asperity 15-15 and 30-30 at different normal stress is compared with the shear behaviour and failure process of numerically simulated rock joint. Indian Geotechnical Conference – 2010, GEOtrendz December 16–18, 2010 IGS Mumbai Chapter & IIT Bombay
On the shear failure of incipient rock discontinuities under CNL and CNS boundary conditions: Insights from DEM modelling
Abstract This paper presents a numerical investigation of the effects of boundary conditions, i.e., constant normal load (CNL) and constant normal stiffness (CNS), on the failure mechanism of incipient rock discontinuities in direct shear. A series of numerical simulations were performed using the particle-based discrete element method (DEM), in which rock matrix and rock bridges (on incipient joint planes) were modeled as an assembly of rigid particles that were bonded together at their contacts. Smooth-joint model was assigned to particles of the persistent portions of incipient rock joints. Input micro-parameters of particles, bonds and smooth-joint were calibrated against a series of laboratory experiments. The study reveals that CNL and CNS boundary conditions significantly affect shear characteristics of incipient rock discontinuities. Peak shear stress increased significantly (up to three times) in the CNS direct shear in comparison with that measured in the CNL direct shear under the same initially applied normal stresses. The significant increase of shear stress in the CNS direct shear tests conducted in this study was related to the opening of newly created micro-cracks and creation of the rupture zones within the rock bridges, leading to a dramatic increase in the normal stresses. In the meanwhile, yield behavior was observed in the CNS direct shear while brittle failure was noticed in the CNL direct shear. It is also found that micro-cracks initiated at the vicinity of rock bridges in both CNL and CNS shear tests, while they propagated differently due to the gradual increase of normal stress under CNS boundary conditions.
Mathematical Modeling of Scour and Deposition
Electronic computers are opening up the field of sedimentation engineering by permitting the analysis of problems which heretofore have required too much time and effort. Movable stream bed profiles are being calculated in addition to water surface profiles. The initial gradation of sediment material in the stream bed may be prescribed to facilitate the calculation of an armor layer. This gradation is continually changed by the computer program in response to sediment particles being deposited on the stream bed and material on the stream bed being removed to satisfy transport capacity. Hydraulic sorting of sediment by grain size is accomodated. The stream bed does not have to be represented by a single grain size. Retardance of motion because of armor layer is calculated.