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

岩石所处的初始应力状态及开挖等工况诱发的卸荷速率大小对其力学特性具有明显的影响,通过室内三轴卸荷试验和破裂断口的SEM细观扫描分析,研究高应力环境中不同卸荷速率下锦屏一级水电站大理岩的变形破裂及强度特征。卸荷速率vu和初始围压σ30越大,岩石脆性及张性断裂特征愈明显,快速双向卸荷时甚至可在次卸荷方向产生张拉裂缝。张性破裂断口细观形态随vu和σ30的增大依次呈现"树枝形张裂状"、"千层饼形撕裂状"和"近光滑平面形弹射状";卸荷过程中轴向压缩应变增量Δε1随vu和σ30增大而减小,而侧向膨胀应变增量Δε3却增大;不同的卸荷变形阶段卸荷速率vu对变形模量E的影响规律不同,峰前E随vu的增大而增大,而峰值E随vu增大先逐渐增大再迅速降低;卸荷过程中岩石的泊松比μ逐渐增大,并随vu和σ30增大而显著,特别是从峰值点后;相对于加载试验,卸荷条件下岩体的黏聚力c大大减小,而内摩擦角?却有少量增大,vu越快,c减小得越多,?增大的较少。

EXPERIMENTAL RESEARCH ON AFFECTION LAWS OF UNLOADING RATES ON MECHANICAL PROPERTIES OF JINPING MARBLE UNDER HIGH GEOSTRESS

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.