Analytical study of dynamic friction mechanism in blocky rock systems

Abstract

Underground excavations such as tunnels, storage caverns, and underground power plants have been constructed throughout the world. Rock masses in underground constructions always contain discontinuities such as faults, joints, bedding planes, and fractures. These discontinuities intersect with each other to create rock blocks [1]. One of the most important problems in underground excavation is the accidental falling of rock blocks at the working faces [2]. To predict this, the removability and stability of the rock blocks around the underground tunnels and caverns must be evaluated based on the characteristics of the discontinuities in the rock masses. The most commonly used method is the block theory developed by Goodman and Shi [3]. A complete block theory analysis consists of removable block identification based on geometric and topological methods, mode analysis to determine whether the removable block has a mode of failure or not, and stability evaluation to identify the key blocks by incorporating comparatively simple mechanics analysis. After that, the supporting force and directions are designed to make sure that the key blocks are stable. If the key blocks are stable, the entire rock mass will be stable [4]. Block theory has been applied widely in rock engineering since early 1990s [5]. However, its stability evaluation is based on static analysis. Recent studies demonstrate that sometimes an external dynamic disturbance may dominate the system behavior. The traditional stability analysis based on static analysis may underestimate the rock instability if not taking these dynamic factors into account. Earlier researchers [6–8] observed that when a pulse loading is applied to a blocky rock system, friction between the blocks in the orthogonal direction to the pulse loading may be significantly reduced or even disappear, which is known as an ultra low friction