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 Effect of Grain Size on Rock Behavior under Cyclic Loading by Distinct Element Method
field to identify the dynamic behavior of rocks in more detail. Nevertheless, the nature of dynamic failure in rocks has not yet been identified, particularly when it comes to cyclic loading The purpose of this study was to investigate the influence of grain size on the mechanical behavior of rocks under cyclic loading using numerical modeling by UDEC. A total of three grain -categories with a diameter of 1, 2, and 4 mm were modeled in the software. All models were of Brazilian type with 54 mm diameter. Behavioral parameters required for modeling were determined through laboratory studies and the software was adjusted accordingly. The stresses applied to the samples were in two forms of quasi -static and cyclic loading. The result of static loading is that the smaller the grain size, the model will have a higher elastic modulus. In other words, the elastic modulus of the grain size is inversely related to the grain dimensions. Analysis of data obtained from cyclic loading showed that the amount of strain in samples with smaller grain sizes was lower than the corresponding strain in samples with larger grain sizes during the same loading periods. In other words, the resistance of samples with smaller grain sizes to deformation under cyclic load was higher compared to those with larger grain sizes. Comparison of the stress vectors for these samples sho wed that with a decrease in grain size, stress distribution in the sample became more uniform and inclusive, and the stress concentration declined. Another important result was that the smaller the grain size, the more the axial stress applied to the sampl e inclined towards one. This indicated that with a decrease in grain dimensions, the sample behavior approached a plastic behavior.  UDEC Software
Shear behaviour of idealized infilled joints under constant normal stiffness
The shear behaviour of soft joints containing infill materials was investigated in the laboratory under constant normal stiffness (CNS) conditions. Tests were conducted on joints with asperities having inclinations of 9·5° (type 1) and 18·5° (type II), under a given range of initial normal stresses (σno) 0·30 to 1·10 MPa, and at a constant normal stiffness of 8·5, Kn/mm. It was found that the shear strength of joints decreases considerably even with the addition of a thin layer of infill. Results also show that the effect of asperities on shear strength is significant up to an asperity height to infill thickness (t/a) ratio of 1·4—1·8, whereas the shear behaviour is controlled by the infill alone beyond this critical ratio. The shear displacement corresponding to the peak shear stress is considerably reduced once the infill starts to govern the shear behaviour of the joint. In this study, the drop in peak shear stress under CNS conditions has been modelled by a hyperbolic relationship. In relation to ‘cle...