Papers by Author: Qian Sheng

Abstract: As a special kind of engineering material, the mechanical properties and failure characteristics of rock directly determine the safety of the engineering works. In this paper, to estimate the indicator of rock failure under seismic loading, the axial plastic strain development of basalt under different lithology and different frequency is studied based on triaxial cyclic loading test. A magnitude of 10-3 is obtained for the critical plastic strain of basalt at failure. The mean value of critical plastic strain is 0.003. A seismic analysis of underground powerhouse complex of the Baihetan HPP is then conducted as a study case. The development of rock mass's plastic strain with seismic loading is studied, and failure zones which have the worst effects on the complex are revealed.

Abstract: For the Three Gorges granite, a finite difference software package FLAC was used to study failure process of heterogeneous rock material. Based on mineral components identification results of the granite and fuzzy clustering method, the actual image date was transformed into the finite difference grid by applying image processing techniques. A convenient and efficient two-dimensional numerical modeling method for heterogeneous geomaterials was presented. Then, failure process of the granite were simulated in uniaxial compression test based on experimental strain soft model, and the stress concentration phenomenon was analyzed. The results show that the numerical modeling method based on digital image processing can be used to calculate the mechanical responses of geomaterials by taking their heterogeneities into considerations.

Abstract: Based on the uniaxial and triaxial compression tests of Three Gorges granites，the crack initiation stress under different confining pressures can be obtained by studying the crack strain curves. The results show that the crack initiation stress changes at the same extent with confining pressure, and is generally located between 25% and 50% of the peak strength. Moreover, the crack initiation criteria and progressive damage model are established, and some beneficial conclusions are drawn. The tension concentration model of elliptic crack can be used to explain cracking mechanism of Three Gorges granite at relatively low confinement, and Three Gorges granite mainly occurs lateral damage in the microfracturing process and exhibits the similar damage evolutionary rule under different confining stress. The damage model can be used to describe the crack propagation process.

Abstract: In this paper, three-dimensional(3D) Numerical Manifold Method (NNM) based on hexahedron element cover with full first-order cover function is proposed and the shape function of C8 isoparametric element in FEM is used as the cover weight function. All sub-matrices in equilibrium equations, including stiffness matrix, initial stress matrix, point force matrix, surface force matrix, body force matrix, inertia force matrix, contact matrix and friction matrix, are derived. Different with 2D contact, the direction of shear stiffness and friction force can not be easily defined in 3D contact. A new iterative method based on vector theory to detect the contact direction is developed. The application of 3D NMM in underground excavation is also presented and show good agreement with real engineering.

Abstract: It is very important to study the pristine stress field in Civil, Mining, Petroleum engineering as well as in Geology, Geophysics, and Seismology. There are various methods of determination of in-situ stress in rock mass. However, hydraulic fracturing techniques is the most convenient method to determine and interpret the test results. Based on an hydraulic fracturing stress measurement campaign at an underground liquefied petroleum gas storage project which locates in ZhuHai, China, this paper briefly describes the various uses of stress measurement, details of hydraulic fracturing test system, test procedure adopted and the concept of hydraulic fracturing in arriving at the in-situ stresses of the rock mass.

Abstract: The power house of Yantan extended hydropower project, with complex geological conditions such as fault f211 below the power house and quartzite on top of it, is a huge underground cavern with large span and high wall. In order to evaluate the stability of the power house surrounded by such complex geological structure, the numerical simulation excavation of power house with different location schemes were studied by the elasto-plastic 2D FEM method. The deformation and evolutive process of the stress with the progress of excavation were analyzed. On the condition ensuring the whole stability of surrounding rock mass, comparison optimization analyses were conducted on the power house location scheme. The rational location scheme was demonstrated. The final analyses results show that: (1) The mechanical properties of quartzite and its relative location to the power house has no obvious influence to the stability of surrounding rock mass.(2) The f211 is the main bad geological structure which affect the stability of power house. (3) The case of moving 10m upward of power house is the most rational scheme for the whole stability of power house. (4) The Supporting measures, which would has an obvious effect in controlling the influence on the stability of surrounding rock mass by weak geological structure, are suggested at the out-crop of f211.

Abstract: In light of the open deformation of joints in the middle isolated pier of the permanent shiplocks of Three Gorges Project(TGP), a typically simplified joint model is set up based on the geological conditions and the crack investigation. The method of joint interface element is used to analyze the joint open deformation and study the characteristic of open joints. The results show that the open deformation and the open length of joints are directly related to their occurrence and geometrical character.