A new parameter to describe the persistency of non-persistent joints

Mechanical behavior of rock with a single non-persistent joint was studied by numerical simulations using two-dimensional Rock Failure Process Analysis (RFPA(2D)) software. A non-persistent joint within the model specimens was arranged with different number of joint segments, but keeping the overall length of the joint same for all cases and the simulations were repeated for three overall joint lengths. For all those different joint arrangements, persistency of the non-persistent joint, as determined using existing definitions for persistency in the literature, was unchanged. However, the results of the numerical simulations displayed a marked difference in the strength for different joint arrangements, in which the increasing number of joint segments increases the strength. This surprising behavior was attributed to the difference in stress distribution patterns within the specimens for different non-persistent joint arrangements. When the number of joint segments is higher, the stress is more diffused within the model specimen such that initiation of the failure fracture is difficult compared to a situation where only very few joint segments (thus few discontinuous joint ends) are existing and the stress is greatly accumulated on those discontinuous joint ends allowing the failure fracture to initiate at lower stresses. By taking this effect into consideration, this paper proposes a new parameter to better describe the persistency of a nonpersistent joint. The new parameter was observed to strongly correlate with the strength of rock, indicating its suitability to represent the persistency of a non-persistent joint. (C) 2014 Elsevier B.V. All rights reserved.