Investigation Into Time-delayed Mechanism Of Rockburst Based On Brittle Creep Failure

With the increasing demand for resource exploration and exploitation,transportation and water conservancy facilities,the construction of deep underground engineering in China develops rapidly and also faces further challenges.The rockburst commonly occurs in deep rock engineering especially during the tunnel excavation process,and most rockburst events exhibit the time-delayed characteristics,which poses a serious threat to the construction stability and personnel security.Therefore,the formation mechanism,prediction and prevention of time-delayed rockburst disaster grabs more attention of scholars and engineers.In view of the above,the research on time-delayed failure of surrounding rock in deep tunnel is conducted according to the failure process of hard and brittle rock and the main contents are as follow:(1)The creep compression tests on various deep brittle rocks are carried out in a multi-level way.The comparative evolution properties of dry and saturated quartz sandstone concerning axial,lateral and volumetric deformation,Poisson’s ratio and relationship between stress level and steady creep rate are obtained,and the effect of moisture condition during the creep failure process is analyzed.The failure process of granite with multi-stage stress is monitored in real time via the digital image correlation(DIC)and acoustic emission(AE)technology,and the characteristics of external surface strain field variation and the evolution laws of internal damage accumulation are respectively obtained.(2)The multiple numerical simulation tests are conducted studying the time-dependent behavior of brittle rock with various homogeneity.The evolution relationship between stress level and strain rate,characteristics of dilatancy deformation and creep failure mode of rock are analyzed,and the influence laws of homogeneity on related creep properties of brittle rock are obtained.(3)A theoretical method is proposed.By combing the creep evolution model of brittle rock based on the microscopic wing crack development model and the analytic model for deep tunnel section with a circular shape,the generation mechanism of time-delayed rockburst induced by the time-delayed failure of surrounding rock of tunnel is investigated,indicating the effect of creep failure of brittle surrounding rock.Based on the results of theoretical study,the approach about the combination of numerical simulation and creep model is further proposed to acquire the range of strong and weak excavation damage zone and creep failure duration on corresponding critical positions,and the delayed failure characteristics and laws of surrounding rock in deep tunnel are analyzed and obtained under the conditions that concerns the geometric dimension and shape of tunnel section and the depth of tunnel.(4)The properties of Qinling granite including creep macroscopic failure and microscopic fracture are observed and analyzed.According to the creep model of brittle rock,the X-ray 3D microscopy scanning test,subcritical crack growth test and indoor compression test are performed to obtain the essential mechanical parameters on macroand micro-scales composing of initial damage,fracture toughness,stress corrosion index,characteristic crack speed,etc.,and the experimental relationship between axial and lateral stress under the crack initiation condition.Based on the raised method regarding the combination of numerical simulation and theory,the phenomena and characteristics of the time-delayed rockburst generated in deep diversion tunnel of Qinling Mountains are verified and comparatively analyzed from perspective of space and time.