Repeated shear mechanical properties and constitutive model of jointed sandstone under heat-wet cycles

The large reservoirs of Wudongde and Baihetan are located in the typical dry and hot valley of the Jinsha River. The rock and soil masses in the fluctuating zone of the bank slope are affected by the annual large rise and fall of the reservoir water level and the small frequent changes during the flood season, as well as the high temperature and low humidity climate conditions in the dry and hot valley, regional high-frequency earthquakes and reservoir earthquakes. In order to study the damage and degradation characteristics of jointed rock masses in the dry hot valley region, based on the previous researches on water-rock interaction, a repeated shear test on the jointed sandstone under heat- wet cycles is conducted in a typical bank slope in Wudongde reservoir area. The degradation law and mechanism of shear mechanical properties of jointed rock masses are analyzed, and a shear constitutive model for the jointed sandstone considering heat-wet cycling damage in sections is established. The results show that: (1) Under the action of heat-wet cycles and repeated shear, the shear strength, shear stiffness, shear expansion value and yield-point shear displacement of the jointed sandstone exhibit a "fast-slow-stable" deterioration trend. Among them, the degradation amplitude is significant in the first three cycles, accounting for nearly 70% of the degradation rate. The degradation rate slows down within 3 to 8 cycles, and stabilizes after 8 cycles. (2) Compared to the dry-wet cycle, the heat-wet cycle has a greater impact on rock porosity and longitudinal wave velocity, and the connection between rock particles is more susceptible to damage at higher temperatures. (3) According to the characteristics of shear stress-shear displacement curve, the modified constitutive model described by Goodman model and Clough-Duncan hyperbola model is established, and the model curve is in good agreement with the test results. The research results and methods can provide reference for the stability analysis of the rocky bank of reservoirs in dry hot valley.