In this study, the solid rock is represented by an assembly of particles joined together by breakable bonds using PFC3D. The contact bonding model supported in PFC3D can transmit a force which acts only at the contact points and it consists of shear and normal strength components. No slip is possible when the contact bond remains intact, but it offers no resistance to rolling. While determining the micro parameters of the model, the effect of stiffness of the particles on Young's modulus and Poisson's ratio are studied. The effect of confining pressure is studied by considering the values corresponding to typical overburden pressures. Along with the stress strain plots at various confining pressures, the extracted micromechanical data are also presented to analyze the strain softening behaviour with special emphasis on the breakage of the bonds. The variation in the strength and mechanical behaviour of the rock masses with respect to the bond strength is thoroughly studied by conducting axisymmetric triaxial tests. The effect of varying bond strengths on the uniaxial compressive strength is also studied at various confining pressures. It can be clearly seen that as the bond strength increases, the compressive strength also increases. Further as the confining pressure increases, there is an increase in compressive strength for the same contact bond strength. Similarly the variation of the values of cohesion and angle of internal friction are also studied for various values of bond strengths. The parametric studies indicate that as the bond strength increases, there is a linear increase in the value of cohesion at various confining pressures, but the angle of internal friction remains almost the same with minor fluctuations.
Majority of the earth"s crust is covered by sedimentary rocks which are formed by the sedimentation of materials. In due course of time, they will be deposited in layers forming rocks and their strength will depend on various factors including the matrix which bind these particles together. Usually the damage of rock masses occur when the entire bond breaks and the material changes from solid to granular material. Sandstone is a type of sedimentary rock which is comprised of rock fragments or minerals held together by natural cementing materials. Depending upon the strength of the cementation, the behaviour of the rocks also changes. Numerical simulations adopting discrete element method generally represents rock mass as an assembly of particles joined together by breakable bonds. The Bonded Particle Model (BPM) suggested by Potyondy & Cundall [1] states that particles can be bonded together at contacts forming a cemented granular material and the macro-scale mechanical behaviour of this cemented material can be related to the rock mass behaviour. But the suitable selection of the particle-contact parameters for the modeling is very challenging. Unless suitable particle-contact parameters are used, the macro-scale response of the modeled block will not be reliable. Experimental studies have showed that the behavior of intact rock in compression is complex, resulting in a nonlinear failure envelope with high frictional resistance [2].