A coupled thermo-mechanical model for investigating cracking and failure of composite interbedded rock

Abstract

Composite interbedded rock is a special geological phenomenon that occurs when layers of rock (beds) of a given lithology lie between or alternate with other layers of a different lithology. The thermal and mechanical properties of the composite interbedded rocks exhibit strong anisotropy. Studying the thermomechanical coupling properties of natural composite interbedded rocks using existing experimental techniques is challenging. A novel thermal-mechanical coupled composite interbedded rock model was developed based on Fourier's heat-conduction law and Newton's second law. The thermodynamic responses and biaxial mechanical properties of composite interbedded rocks with different interlayer angles under the coupling of initial stress and thermal loading were studied for the first time. The results indicate that the thermal stresses within the granite interlayers are higher than those within the sandstone interlayers. Throughout the thermal loading process, thermal cracking occurred primarily within the (stiffer) granite interlayers. The number of thermal cracks generated during the cooling process far exceeds that during heating; at 400 °C, the number of thermal cracks during cooling is more than 35 times that during heating. When the interlayer dip angle approaches 90° and is aligned with the major principal stress direction, the phenomenon of the “double peaks” and layered failure becomes more pronounced. Within the range of variables considered, the relative impact of the three variables on peak stress in composite interbedded rock is as follows, from greatest to least: interlayer angle, thermal shock temperature, and model size. The results and developed modeling methods will contribute to the management and optimization of future engineering geology projects.