Study On The Stability Of The Underground Cavern Group Under The Conditions Of Different In Situ Stresses' Characteristics And Different Yield Criteria

China is abundant in water resources, especially in the southwestern areas. In recent years, a large number of hydroelectric power stations are being and will be built. Meanwhile, these projects locate in mountain areas, and underground excavation is abosolutely a development trend in the underground cavern group of the hydroelectric power stations. Therefore, study on the stability of underground caverns is a significant research topic.The stability of the surrounding rock masses in underground caverns is a multi-factor problem, and the in situ stress is the most important. Taking the underground caverns of Shuangjiangkou Hydroelectric Power Station as an engineering background, the differential numerical analyses software FLAC³D was utilized to study on the influences of different characteristics of in situ stress to the stability of surrounding rock masses considering four characteristic factors: (1) the main physico-mechanical parameters of the surrounding rock masses; (2) the embedded depth of the caverns; (3) the lateral pressure coefficient and (4) the included angle between the direction of the cavern(?)longitudinal axis and that of the horizontal maximum principal stress. Based on the analyses of these factors and the proposed expression that can predict the displacements of the key points on the high side walls, this paper put forward a modified formula which can predict the displacements of the key points in a true three dimensional state. As for the factor (4) mentioned above, the included angle in different in situ stress conditions which are appropriate for the stability of the surrounding rock mass was obtained in this paper according to the criteria below: (1) to achieve the minimum displacement of the high side walls; (2) to attain the minimum volume of plastic zones, and (3) to get the minimum volume of splitting zones.For the weakness of the post processing in FLAC^3D, based on the FLAC^3D -Tecplot data conversion program, the criterion of splitting failure was involved in this program, then the splitting zone can be obtained when the data has been converted.In the analyses of the stability of surrounding rock masses, to select the yield criterion is also an important component. On a basis of Zienkiewicz-Pande shear yield condition and adding a tension yield function, a complicated constitutive model whose failure envelope involves a Zienkiewicz-Pande criterion (shear yield function) with tension cutoff (tension yield function) was established in this paper. Taking FLAC^3D as the development platform, the above constitutive model was written in the VC++7.1 compiling environment. Eventually, the surrounding rock mass stability of the underground cavern group of Shuangjiangkou hydroelectric power station was analyzed through the Zienkiewicz-Pande model and other three models in FLAC^3D: Mohr-Coulomb model, Druker-Prager model for the outer adjustment and Druker-Prager model for the inner adjustment. According to the comparative results and the failure characteristics of surround rock mass after excavations, the influences of different yield criteria to the stability of surround rock mass are verifiedbased on the indexes of surrounding rock mass failure, and the model is basically reasonable and correct.