Micromechanics Study On The Failure Mechanism And Stability Of Deep Buried Surrounding Rock Of Underground Cavern

Widespread construction of deep buried underground caverns is the inevitabledemand of human survival and development in the future. At present, the failuremechanism and stability of surrounding rock is one of the key and difficult problemsof the geotechnical engineering at home and abroad. Relied on one deep buriedunderground cavern in the Western China and based on particle flow theory, physicalexperimental principles, centrifugal model theory and overload method, this paperanalyzes the failure mechanism and stability of deep buried surrounding rock ofunderground cavern from six aspects and macro-micro point of view. The results ofthis study are listed as follows.（1）Mechanical behavior of the deep-buried hard rock. The mechanicalbehavior of siltstone is influenced by loading method, confining pressure andunloading rate. The time of microcracks forming largely is post and close to peakstrength, and its distribution and number is related to loading method, confiningpressure and unloading rate, which is the essential reason of different failure modes.（2）Failure mechanism of the hard rock with a pre-existing hole. The failurerule of siltstone with a pre-existing hole is basically the same as that of wholespecimen, but is influenced more easily by loading method and confining pressure.The size and direction of intermediate principal stress have a significant effect onmechanical behavior of siltstone, and its failure feature (brittleness or ductility) isdeterminated by minimum principal stress and the difference of intermediate andminimum principal stresses. Meanwhile, its failure modes of siltstone specimen aredetermined by the amplitudes and directions of intermediate principal stress, and arerelated to weakening effect of the opening and inhibition effect of confining pressurein essence.（3）Failure mechanism of underground caverns with different sections. Thefailure modes and failure processes are different between "loading before excavation"and "loading after excavation". Sections and lateral pressure coefficients have animpact on stress redistribution after excavation, which leads to the differences of theformation, propagation and distribution of microcracks. Lateral pressure coefficient within limits is benefit for the stability of underground caverns. But the critical valuesof lateral pressure coefficients are different with different sections.（4）Rockburst’s failure mechanism of deep buried underground cavern. Nomatter whether loading or unloading tests of rock burst, the change rules of stress andenergy during the process of rock burst is fundamentally the same. However, thespecific failure mechanism of rock burst is different when test modes and/or minimumconfining pressure are different. And the influence of minimum confining pressure onunloading or loading tests of rock burst is discriminatory.（5）Stability study of deep buried surrounding rock of underground cavernduring the excavation process. When lateral pressure coefficients are different, failuremechanism of underground cavern, possible rock burst’s types and the spatial andtemporal distribution of AE are different. On the whole, damage zone firstly forms onthe surface of tunnel wall and excavation face by excavation disturbance,subsequently develops toward the deep areas with the advance of excavation face.And its development is related to lateral pressure coefficient.（6）Influence of joints on the stability of deep buried underground cavern.Based on particle flow code, numerical program of direct shear test is compiled andapplied to relate the microparamaters of joints and its macromechanics features.According to the statistical law of joints’ distribution in real rocks, subroutine ofrandom intermittent joints is compiled and embedded in particle flow code. Whenconnectivity rates of joints are different, specific failure modes of surrounding rockduring the excavation process, the distribution of microcracks and comprehensivedisplacements are different. On the whole, the buckling failure possibility ofsurrounding rock increases with the increase of connectivity rates.