Superbrittleness of rocks at high confining pressure

Abstract

The paper discusses the variation of rock brittleness with confining pressure 3 for rocks of different hardness, failed under triaxial compression with 1 > 2 = 3 . Experimental results presented in the paper show that hard rocks unlike relatively soft rocks increase their brittleness with rising confining pressure 3 . The harder the rock the greater is the effect of embrittlement. Most hard rocks become hundreds of times more brittle compared with uniaxial compression approaching absolute brittleness. The shear rupture energy at these conditions becomes vanishingly small. Estimations made for Westerly granite show that the maximum brittleness corresponds to 3 300 MPa.