This paper studies the problems of stability and supports of an underground power plant which consists of a qroup of big caverns. The power plant is designed to be located in limestone, where three faults and two clay partings pass through. Due to the complex conditions of rocks, the nonlinear FEM is used to analyse the various ways of excavations and supports, so as to gain an optimum designing scheme.
East Wind Hydropower plant is an important project in Guizhou Province of China in designing. It is going to be constructed in a narrow valley of Wujiang River for Controlling the water of upper region of 181 square km. The project consists of an arch dam, an underground power plant and a bank spill way. The power plant, which will installed with three water-turbine generator sets in total capacity of 510 MW, has two-three parellel big caverns of main mahine hall, main transformer room and tail water surge chamber, which connect transversely with the tail water tunnels, gate shafts and electric cable galleries. Of the group of caverns, the main machine cavern is the biggest, which is 39 metres in height and 21 metres in Width. The strata in site are medial thick and thin layers of limestones, bended clayey limestone and shale, distributing from top to bottom. By the crown of caverns, there are two clay partings, passing along the rock layers with a low inclination of 8.7 degrees. Otherwise, the three faults intersect at cavern area with high inclination of 68.8 and 118 degrees. So the rocks are cut into blocks by layers and joints under the effects of geological structure. These cases cause the unstable condition to the underground power plant, Fig. 1.
(Equation in full paper)
During the planning period of the project, a lot of geological prospecting Was conducted. The ground stress was measured in a heading adit at the crown of main machine cavern. The values gained Sketch of Condition of Strata show that the lateral ground stress is two times greater than that at vertical. To get the reasonable design, the influence of various excavation sequences and the support systems on the stability of the cavern group was studied by using the nonlinear finite element method.
Since the strata of lower inclinatlion intersect with a set of weak joints of higher inclination, the rock mass can be seen as a compisotion of rock blocks and weak joints, which appears a nonlinear and anisotropic behavior. The hyperbolic 227 constitutive relation is used in FEM Where:
Et and Vt- tangential elasticity modulus and Poisson's ratio; (~1-d3)- principal stress difference; (d1-d3)ffailure principal stress difference; Rffailure ratio, (d1–03)/(d1–03)ult; (d1-d3)ult- ultimate principal stress difference; Pa- atmosphere pressure and K, n, G, F and d-constants. Equation in full paper considered to be affected by weak joints, which presents the anisotropy of strength and faiture mechanism. The research results indicate that the failure modes are related to the stress state and structure behavior of rock mass very much. If the intersective angle between shearing direction and joint plane is greater than some 67.5 degrees, the failure should take place through rock blocks. In this case, the failure strength can be described
