Papers by Author: Xiu Run Ge

Abstract: The purpose of this paper is to study the shear behavior of rock specimens containing joints with various distribution forms. Two sets of specimens are simulated by the rock failure process analysis code (RFPA2D). The friction-sliding failure pattern occurs with the lower undulation angle specimen, and the failure pattern turns to be tensile-shear failure mode gradually with the increase of undulation angle. The specimen possesses the highest peak shear load when the undulation angle is about 30º. And joint rock shear character also deteriorates with the increase of weak interlayer thickness. In the intermittent joint model, the unified connection ratio specimen’s peak shear load increases with rock bridge amount, and the multi-joint mode is beneficial to keep rock mass shear stiffness. This study comes to meaningful results to the expansion of joint rock strength evolution law with various joint distribution forms.

Abstract: In geotechnical engineering, based on the theory of inverse analysis of displacement, the problem for identification of material parameters can be transformed into an optimization problem. Commonly, because of the non-linear relationship between the identified parameters and the displacement, the objective function bears the multimodal characteristic in the variable space. So to solve better the multimodal characteristic in the non-linear inverse analysis, a new global optimization algorithm, which integrates the dynamic descent algorithm and the modified BFGS (Brogden-Fletcher-Goldfrab-Shanno) algorithm, is proposed. Five typical multimodal functions in the variable space are tested to prove that the new proposed algorithm can quickly converge to the best point with few function evaluations. In the practical application, the new algorithm is employed to identify the Young’s modulus of four different materials. The results of the identification further show that the new proposed algorithm is a very highly efficient and robust one.

Abstract: A numerical technique based on using manifold elements in finite element method, for modeling propagation of arbitrary cracks in solids, is described. When the region with crack(s)is subjected to external loading and the crack(s) starts to extend, the crack growth may intersect boundaries of nearby finite elements. Those intersected finite elements are replaced by manifold elements. The technique, by which the initial finite element mesh can be kept unchanged during the processes of crack propagation, is called manifold elements in finite element method. The crack growth is governed by the theories of linear elastic fracture mechanics. The stress intensity factors are computed by a contour integral technique and crack trajectory is determined by applying the maximum tangential stress criterion. Finally, test examples are given to verify the new method and the predicted trajectories are compared to experimentally obtained crack growth paths with good agreements

Abstract: A series of formulas about two-parameter parabolic Mohr strength criterion(2-PP Mohr criterion) are derived. Based on the results of uniaxial tension and uniaxial compression tests, the parameters involved in the criterion can be easily determined, then the criterion in terms of the major principal stress and the minor principal stress is derived, and the damage pattern is also discussed. At last, the formulas about the rupture angle and the friction angle are presented, and their relationship is also given. 2-PP Mohr criterion can describe not only shear but also tensile failure. In this criterion the ratio of the uniaxial compression strength and the uniaxial tension strength is not confined as in Griffith criterion. The formula about the rupture angle provides steady theoretical foundation for determining the direction of crack faces and damage patterns in the computation of macro crack propagation. In fact, Griffith criterion is only a special case of the two-parameter parabolic Mohr strength criterion proposed in this present paper.

Abstract: In finite element method, the order of complete polynomial of the interpolation function is related to the number of nodes in the element. This paper presents a four-node quadrilateral element with quadratic function on it. The presented displacement functions maintain C0-continuity. Meanwhile, the element stiffness matrix is derived from the displacement functions. Test problems show that high accuracy can be achieved by the use of the new displacement function on the element.