EXPERIMENTAL RESEARCH ON AFFECTION LAWS OF UNLOADING RATES ON MECHANICAL PROPERTIES OF JINPING MARBLE UNDER HIGH GEOSTRESS
高地应力条件下卸荷速率对锦屏大理岩力学特性影响规律试验研究

The mechanical properties of rocks are obviously affected by initial stress state and unloading rates that are caused by excavation. Based on triaxial unloading and scanning electron microscopy(SEM) analysis,the deformation,breakage,and strength features of marble samples of the Jinping First Hydropower Station under different unloading rates and geostress conditions are studied. With unloading rates v_u and initial confining pressureσ_3~0 increasing,the brittle rupture and tensile characteristics of rock are more obvious. There are annular tensile cracks in secondary unloading direction when the rock samples are unloaded in two directions;and the meso-shapes of the tensile fracture surface under SEM consequently are presented with branch-tension,and multilayer biscuit-lancinated and slippery plane-ejected shapes. The axial strain compression increment Δε_1 is gradually reduced,but the confining expansion stressΔε_1 is increased during the process of unloading. The influence of unloading rate v_u on deformation modulus E is different at the different deformation stages during process of unloading. The deformation modulus E is gradually increased before peak strength,but it gradually increases firstly and rapidly decreases afterward with v_u enhanced. The Poisson's ratio μ is gradually increased during process of unloading,and it is more distinct with v_u andσ_3~0 enhancing,especially after peak strength. Relative to data of traditional triaxial loading test,the rock cohesion c is remarkably reduced but inner friction angle φ is a little increased under unloading test. The faster the v_u is,the more c is reduced,and the less theφ increases.