Experimental Study On Time-efficiency Characteristics Of High-stress Hard And Brittle Rocks

With the increasing energy exploitation,mineral resources exploration and development,nuclear waste disposal,the scale of underground rock mass engineering is becoming larger and deeper.Deep rock mass engineering often has the characteristics of high buried depth and complex occurrence environment,which is more difficult to build than ordinary underground engineering and has a long service period.Therefore,it is necessary not only to ensure the stability of surrounding rock during construction,but also to avoid the instability of surrounding rock during operation.Therefore,the long-term stability of deep engineering rock mass has become a scientific problem to be solved urgently in the development and utilization of deep underground space.Aiming at the problem of stability analysis and control of hard surrounding rock in high stress underground caverns,the time-effect mechanical properties of high stress granite are studied by means of in-situ observation of time-effect characteristics of surrounding rock and indoor triaxial creep test of damaged rock,taking the underground powerhouse caverns of Shuangjiangkou Hydropower Station as the engineering background.The main contents and conclusions of the study are as follows:(1)Based on the cases of time-effect deformation and failure of rocks existing in the field and combined with the structure of surrounding rock and external environment,the causes of time-effect deformation and failure of granite are systematically analyzed.Based on the data monitored by field base station,the time-effect mechanical behavior of granite surrounding rock in underground powerhouse cavern of Shuangjiangkou Hydropower Station is analyzed from four aspects:deformation,sound wave,load and borehole camera.(2)Considering that the excavation of surrounding rock will inevitably cause damage to rock mass,and then the damaged surrounding rock will continue to occur a series of time-dependent mechanical properties of the destruction with the passage of time.In order to analyze the influence of different damage degrees on the mechanical behavior of high stress granite,the instantaneous mechanical properties test and creep mechanical properties test of damaged granite were carried out,and the damage mechanical properties of high stress granite were studied from 2 time scales.(3)The experimental results of instantaneous mechanical properties of damaged granite showed that the macroscopic fracture mode of thermal damaged granite under uniaxial compression gradually transited from tensile splitting to shear-tensile fracture mode,and the microscopic fracture mechanism showed that the initial transgranular fracture gradually transited to intergranular fracture;the brittle splitting failure of granite under mechanical damage was almost consistent with the failure mode of non-destructive granite.(4)The experimental results of creep mechanical properties of damaged granite showed that under the same stress level,the damage evolution rate of damaged granite was higher than that of nondestructive granite,and the creep strain of nondestructive granite was lower than that of damaged granite at any time;the damage evolution rate of granite decreased with the increase of confining pressure,and the stable creep stage of damaged granite was earlier than that of nondestructive granite.Figure[55]Table[9]Reference[57]...