Research On Post-failure Mechanical Properties Of Brittle-plastic Rocks By OOFEM Coupled With IEM

The revolutions of the computational power and memory capacity of modern computing technology offer us a valid implement to calculate more complicated problems only, and the high efficiency of program is our perpetual seek. This thesis tries to act from two aspects: applies object-oriented programming method to advance the development and maintenance efficiencies of programs; applies finite elements coupled with infinite elements to reduce the computational domain of geotechnical engineering so as to advance the calculation efficiency of programs, and service to the numerical simulation of the post-failure mechanical properties of brittle-plastic rocks finally. Therefore, object-oriented programming method, infinite element method and the post-failure properties of brittle-plastic rocks are the themes of this paper. Recapitulatively, several aspects are studied as follows:1. Based on the systemic research of object-oriented programming method, a three-dimensional object-oriented non-linear brittle-plastic finite element analysis model is constructed.2. Applies object-oriented program design language visual C++, embeds Matlab math library and utilizes its powerful matrix operation functions, a geotechnical FEM software (named as EBPFEM) based on Windows98/2000/NT is designed to deal with two or three dimensional problems. This software can execute elastic-plastic and brittle-plastic finite analysis, can preferably simulate mechanical properties of brittle-plastic rocks, can preferably simulate excavation, and can preferably simulate discontinuity between rock mass as well. What's more, this software can simulate infinite or semi-infinite calculate zone which is often involved in geotechnical engineering because infinite elements are incorporated.3. Based on the systemic and comprehensive review and summarize of infinite element method, the fundamental principles of mapping or attenuation infinite elements and the specific construction methods of their shape functions are elaborated respectively, and then shape functions of several mapping or attenuation infinite elements in common use are summarized, and the shape function and some other correlation formulas of a simple and utility infinite element- three dimensional 6 node infinite element are deduced particularly as well.4. Based on the works of predecessors, the classification of complete stress-strain curves of rocks is discussed beneficially. Applies plastic potential theory, the methods of determinations of plastic flow factors between brittle stress drop under different yield criterions are deduced, and a simple and approximate treatment method of the non-zero displacement increment generated between the brittle stress drop when the non-ideal brittle-plastic model involved in is put forward.5. Tests aims to research on the coefficient of brittle stress drop of several brittle rocks such as marble, red sandstone and granite are performed. The researches show: the brittleness of brittle- plastic rocks is relative, and can change to ductility accompanied by the increasing confining stress; the brittle stress drop of brittle-plastic rocks only takes place when the confining stress is small, and the coefficient of brittle stress drop is a function of the confining stress, and such relation expressions about marble and red sandstone are given as well.6. The results of contrast research on different yield criterions of non-linear finite analysis show: in the condition of three-dimension, using different general Von Mises criterions to approximate Morh-Coulomb criterion, Drucker-Prager condition is inclined to conservative, and the accurate one which approximated to Morh-Coulomb criterion is between interior and exterior vertex circle. Interior vertex circle is inclined to be conservative and exterior vertex circle is inclined to be dangerous as well, and so, the equal area circle is the relative well-founded compromise choice.7. The application in the stability of underground excavation of Xiaowan Hydropower Project with different yield criterions proves validity and practicability of the three dimensional elastic-brittle-plastic finite elements coupled with infinite elements analysis software (named as EBPFEM), which can be of beneficial reference to analogous projects.