A novel true triaxial test device with a high-temperature module for thermal-mechanical property characterization of hard rocks

Rock mechanical property testing under high-temperature true triaxial compression conditions is significantly important to understanding the stability of deep underground engineering rock masses where high temperature exists. This article presents the development, calibration and application of a self-designed true triaxial test system for investigating rock mechanical behaviors under coupled high-temperature and high-pressure conditions with cuboid rock samples. The test system is consisted of four independent parts, respectively for mechanical loading in three axis, thermal loading up to 250 °C, deformation and temperature measurement, and the data acquisition center. The key technology and calibration method of the measurement sensors were introduced. The primary testing results of Jinping marble, Bayu granite and Longchang sandstone under high-temperature and high-pressure coupled true triaxial conditions were obtained. It shows that the peak strength, elastic modulus and fracture mode vary with rock types and temperatures. The mechanical property of Jinping marble increases with the increase of temperature in the tested temperature range, while Longchang sandstone shows a decreasing trend, and the change of Bayu granite is relatively small. The fracture mode of Jinping marble, Bayu granite Longchang sandstone at different temperatures is compressive-shear fracture. The results verify the reliability of the test system, and provides a new platform for understanding the mechanical properties of rocks of deep underground engineering with high temperatures.