UNDRAINED SHEAR BEHAVIOR OF SATURATED JOINTED ROCKS AT DEEP BASING CONDITIONS

SHEAR DISPLACEMENT ALONG ROCK MASS DISCONTINUITIES (JOINTS) UNDER SATURATED, UNDRAINED CONDITIONS IS ONE OF THE CRITICAL FAILURE MODES FOR A DYNAMICALLY LOADED DEEP BASE STRUCTURE. THE FAILURE MODE HAS NOT BEEN EXPERIMENTALLY SIMULATED FOR DEEP BASE CONDITIONS. THE COMBINED APPLICATION OF NORMAL AND SHEAR STRESSES AT DYNAMIC RATES, WITHOUT PORE PRESSURE DRAINAGE, IS LIKELY TO PRODUCE HIGH PORE PRESSURES FOR ANY OVERPRESSURE IN WHICH THE JOINT NORMAL CLOSURE EXCEEDS SHEAR-INDUCED NORMAL DILATION. THIS SYNERGISTIC EFFECT OF SIMULTANEOUS SHEAR AND NORMAL LOADING WITHOUT DRAINAGE IS IMPORTANT IN ROCK TYPES CONSIDERED FOR SITING DEEP BASED STRUCTURES, SPECIFICALLY IN WEAK, POROUS ROCKS. THE OBJECTIVE OF THIS RESEARCH IS TO INVESTIGATE PORE PRESSURE RELATED STRENGTH DEGRADATION AT AN APPROPRIATE OVERPRESSURE LEVEL AND DYNAMIC RISE TIME OF INTEREST FOR DEEP BASING TO PROVE FEASIBILITY FOR DETAILED DEFINITION OF THE PHENOMENON IN PHASE II. PHASE I EXPERIMENTAL WORK INVOLVES 24 SHEAR TESTS, WHICH VARY DRAINAGE, STRAIN RATE, ROCK TYPE, AND JOINT ROUGHNESS TO SCOPE OUT THE FACTORS WHICH ARE CRITICAL FOR DYNAMIC, SATURATED SHEAR STRENGTH.