Deep Buried Cavern Experimental And Theoretical Studies Of The Formation Mechanism Of Cleavage Fracture

While the underground openings are being excavated, the rock pillars between the caverns are apt to appear longitudinal splitting cracks, 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 this kind of 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, energy dissipation theory analysis, and numerical simulation and so on. This paper further studies and probes into the shape conditions and mechanism of the splitting cracks, consequently attains a series of meaningful research achievements.From the experiments aspect, we first use the in-situ rock specimens to do uniaxial compressive test, triaxial compressive test and load-unload test with the volumetric strains as damage parameter, so we got the physical mechanical parameters of the brittle rock and analyzed the characteristics of the strength. According to the parameters, we chose a type of mortar as a rock-like material to model the load-unload process of rock pillars when excavating the underground openings. We have developed a triaxial load-unload apparatus by ourselves, which can effectively realize the triaxial load-unload test perfectly model the process of splitting cracks owing to excavating underground openings. The experimental results are as follows: unload can cause the stress redistribution in the rock pillars and stress concentration in part of them. The splitting cracks emerge in the excavation plane which is similar to the characteristics of uniaxial compression. Based on the experimentation result and the energy dissipation theory, the elastic energy change is absorbed by cracks for growth. The energy expressions are obtained under tension and compression conditions respectively. According to the load-unload experimental data analysis, the growth of crack is considered to be influenced by grain scale. As a result, the microcosmic energy model is founded.According to the stress-strain complete process curve, the total volumetric strains and crack induced 1 volumetric strains is adopted as damage parameters for analyzing the five phases during the crack growth (crack closure , linear elastic, stable crack growth, unstable crack growth and post failure). The cohesion and friction is mobilized in the brittle rock.Based on the fracture mechanics, the linear-sliding cracks groups are adopted for analyzing the critical length, interval and stress. Splitting cracks divide the rock pillars into a few thin slabs, whose stress state is similar to the buckling of slabs. According to the corresponding theories on slab buckling and energy dissipation analysis, failure mechanism of rock pillars is studied after appearing the splitting cracks. The critical buckling failure load of slabs is achieved and the predictive formulas about the numbers of splitting cracks are deduced.According to the above result, the criterion of splitting failure, crack density formula and displacement forecasting method are put forward.Based on the energy method in this article and numerical procedure FLAC3D, the total dissipation energy is obtained through tracing the variety of elastic energy density of each element and recording the maximal fluctuation when brittle failure happens during numerical calculation. According to this method, the intension of rockburst and the position and extent of failure zone can be predicted during rockmass excavation under high in situ stress. The criterion of splitting failure and displacement forecasting method is used for contrastive analysis of Er'tan project. The result is accord with in-suit data.Making use of the RFPA^3D which can simulate the heterogeneous of brittle rocks, the failure process of rock pillars between the caverns in Er'tan project is simulated. It is proved that the brittle failure forms of splitting cracks under high in situ stress is the key factor which causes instability of caverns. In the meantime, the physical model test result is testified.