The Study On Theory Of Brittle Failure And Related Issues In Deep Rock

While the underground openings are being excavated, the rock pillars between the caverns are apt to appear brittle failure, which constitute a threat to the stability of the caverns. Especially the deeply embedded caverns under high in situ stresses, they are more readily to appear longitudinal splitting cracks and even intense brittle deformation failure, like rock blast etc. Only a few scholars are interested in further studying these phenomena. This paper mainly studies these phenomena by means of the tools like experimental model tests, site monitoring, theory analysis, and numerical simulation and so on. This paper further studies and probes into the shape conditions and mechanism of the brittle failure, consequently attains a series of meaningful research achievements.Through the analysis of monitoring data of Pubugou underground powerhouse, the distribution and the depth of brittle failure zone in the sidewall were obtained. Monitoring results showed that the method used to monitor was simple and rapid, which can test the brittle failure zone effectively.Based on the fracture-damage mechanics, the collinear crack model was adopted for analyzing the critical length, interval and stress. The crack propagation, damage evolution equation of multi-crack rock mass in the pression-shearing stress field was derived. Moreover, the additional deformation due to the crack propagation was considered. The mechanical degradation index was introduced to reflect the degree of strength loss after attainment of the peak strength. The degradation index can also describe the postpeak degradation exhibited by a rock under different confining conditions (loading and unloading).Based on the shear-lag model, the role of rockbolt was discussed from the point of view of changing the stress state of rock. The existence of rockbolt increased the confining pressure for the sidewall of underground opens. Relationship between fracture toughness and confining pressure was introduced to describe the anchoring effect.Laboratory test based on SHPB(Split Hopkinson Pressure Bar)was carried out considering the stress state of multi-crack rock under with static-dynamic coupling load. The influence of crack angle and confining pressure condition on the additional lateral deformation of rock was discussed. The mechanical response of deep rock pillar, which is under complicated stress condition and then subjected to dynamic disturbance, is numerically simulated.The static load in the sidewall increased after blasting and excavation. Changes of the stress state of rock under the complex load were investigated. The displacements, the depth of tensile stress zone and the maximum value of tensile stress under the complex load were calculated.Based on the above theory, stability analysis of Dagangshan underground openings was carried out with numerical software FLAC^3D. The position and depth of brittle failure zone were predicted effectively during rockmass excavation under high in-situ stress. Optimized support scheme was adopted to reduce the extent of brittle failure zone.