DISTINCT ELEMENT MODELLING OF JOINTED ROCK MASS IN UNIAXIAL COMPRESSION

Abstract

Rocks in nature always occur with some type of discontinuities present in them. The rock mass may be taken as an assemblage of intact blocks with large number of discontinuities embedded in it. The strength and deformation behavior of the rock mass is governed by the characteristics of the discontinuities present in it. The Unconfined Compressive Strength (UCS) is the one of the most important properties of rock which is used by a civil engineer for the design of Civil engineering projects like arch dams, bridge piers, tunnels and underground structures. The objective of the work was to study the effect of anisotropy of the rock on strength and deformation properties by simulating a standard unconfined compression test with Distinct Element Modelling. Universal Distinct Element Code (UDEC) was used in the simulations because of its ability to model behavior of jointed rock mass effectively. In the present study, numerical simulations using Universal Distinct Element Code (UDEC) have been performed to study the behavior of jointed blocks of model material under uniaxial loading. First of all the value of UCS obtained from numerical simulation were compared with those from experimental result for different orientation of joints. Secondary the effect of orientation of joints and size of intact blocks in rock mass on UCS of jointed rock mass was studied. The variation of uniaxial compressive strength of jointed rock mass with orientation of joints and size of blocks shows that the rock mass is highly anisotropic in nature. It was observed that the joint geometry configuration controls the modes of failure of jointed rock mass and four modes of failure were identified, namely (a) sliding along preexisting joint, (b) rotation, (c) large opening along pre-existing joints with creation of voids and (d) material failure. It was found that as the block size increases the UCS of jointed rock mass increases but the increase depends upon the orientation of joints. Also the tangent modulus of jointed rock mass increases as the size of blocks increases. The behavior of constrained and unconstrained rock mass under uniaxial compression mass has also been studied. It has been shown that numerical simulation can be carefully used as an alternative to experimental study and it is suggested that experimental study should be carried out with numerical simulation for greater degree of surety of design parameters for safe and economical design.