The Universal Distinct Element Code (UDEC), developed by the ITASCA Consulting Group, is a “distinctive element program for discontinuum modelling”. UDEC simulates the response of discontinuous media (different rock types) when they are subjected to either static or dynamic loading. Linear or non-linear force-displacement causes movement in both normal and shear directions.
SRK used UDEC modelling on part of the east pit of a gold mine in western China to gain a better understanding of the mechanical behavior of the rocks in the two main joint sets encountered in the east wall, when the upper pit is excavated sequentially, and to provide a basis for the design of the final pit.
Two cases were modelled:
• Model 1: Includes only one set, 1m continuous
• Model 2: Includes both sets, 1m continuous and 4m discontinuous
It was assumed that the horizontal and vertical stresses are equal and are caused purely by their own weight. A strength reduction technique was used to evaluate the factor of safety (FOS). The material strength was reduced to a level where the pit becomes unstable and failure develops. Figure 1 shows the point where the slope becomes unstable, providing clues to the likely mechanical behavior of the pit walls as the pit is gradually deepened.
