Mechanical behaviour and failure mode of Bentheim sandstone under triaxial compression

Hydrostatic and triaxial compression tests have been conducted on nominally dry samples of Bentheim sandstone, a homogeneous quartz-rich sandstone with porosity of about 23%. A broad range of confining pressures were used to observe the transition from the brittle faulting to cataclastic flow regime. Mechanical data for the brittle strength and compactive yield stress can be fitted with empirical envelopes that have been shown to be applicable to other porous sandstones. However, the Bentheim sandstone is somewhat unusual in that quasiductile failure (characterized by an overall hardening trend punctuated by episodic strain softening and compaction band formation) was observed over a wide range of confining pressures from 120 MPa to 300 MPa. Since this failure mode is similar to observations in honeycombed cellular solids, it is speculated that the prevalence of quasiductile failure in the Bentheim sandstone arises from its relatively homogeneous mineralogy and grain size. Compaction band formation may be inhibited in other sandstones with higher fractions of feldspar and clay, as well as more disperse grain sizes. (C) 2001 Elsevier Science Ltd. All rights reserved.