黏土中隧道垮落的塑性分析和数值模拟

~~黏土中隧道垮落的塑性分析和数值模拟@谢骏$伦敦南岸大学!伦敦~~

PLASTICITY ANALYSIS AND NUMERICAL MODELLING OF TUNNEL COLLAPSE IN COHESIVE SOIL

Research on the collapse analysis of underground excavations (tunnels, trapdoors and plane strain headings) is carried out. Through the discussion of the collapse of a single circular tunnel in cohesive soil, the collapse mechanisms of two parallel circular tunnels are established. Employing the bound theorems of plasticity theory, admissible velocity fields and admissible stress fields are created around the two tunnels to obtain upper and lower bounds of stability ratios.Several new parameter definitions: field stability ratio Nf, natural stability ratio Nn. collapse stability ratio Nc are introduced. A new stability analysis plot is derived to analyse the collapse of geotechnical structures, working with the finite element software package-CRISP. Five principal procedures for searching for the collapse stability ratios are developed, based on the stability analysis plot. Under the condition of soil with self weight, the stability ratios for the two tunnels obtained from the finite element method agree well with the solutions obtained using the bound theorems.Two models of three-dimensional trapdoors, square and rectangular trapdoors, are developed to investigate local roof collapse in tunnels. Comparing several trapdoor stability solutions, it is proposed that different trapdoor models (3D block, 3D rectangular and 3D square models) can be used for the stability analysis for the square trapdoors located in different depths. The upper and lower bound solutions for square and rectangular trapdoors are derived and discussed.Block equilibrium analysis method with a triangular element is developed to examine the stability of a vertical cut and a plane strain heading. The force equilibrium equations of a soil structure and yield criterion equations are assembled into a linear programming that is solved with the Simplex Method to obtain optimum stability ratio, via the load factor. This method shows good potential for the collapse analysis of soil structures in geotechnical engineering practice in the future.