Physical and Mechanical Properties of Thermally Cracked Andesite Under Pressure

摘要

The effects of thermal crack damage on the physical properties and rupture processes of andesite were investigated under triaxial deformation at room temperature. Thermal cracking was induced by slowly heating and cooling samples. The effects of heat treatment temperatures ranging between 500 degrees C and 1100 degrees C on the P-wave velocities and on the microstructure were investigated. Then, the mechanical properties of andesite samples treated at 930 degrees C were investigated under triaxial stress at room temperature using constant strain rate tests and confining pressures ranging between 0 and 30 MPa. Similar triaxial experiments were conducted on non-heat-treated samples. Our results show that: (1) for heat treatments at temperatures below 500 degrees C, no significant changes in the physical properties are observed; (2) for heat treatments in the temperature range of 500-1100 degrees C, crack density increases; and (3) thermal cracking has no influence on the onset of dilatancy but increases the strength of the heat-treated samples. This last result is counterintuitive, but seems to be linked with the presence of a small fraction of clay (3%) in the non-heat-treated andesite. Indeed, for heat treatment above 500 degrees C, some clay melting is observed and contributes to sealing the longest cracks.