基于SEM的可變形塊體離散元法研究

周東 張青波 李世海

摘 要：針對邊坡工程中巖土體連續-非連續漸進破壞的特點，提出一種新的變形體離散元方法（DEM）。與傳統有限單元法（FEM）不同，彈簧元法（SEM）通過構建一組廣義彈簧系統描述單元的力學行為。彈簧元法中的一個廣義彈簧可以具有多個方向的剛度系數，確定廣義彈簧系統的構造形式及其各剛度系數表達式是彈簧元法的核心。以三角形單元為例，介紹平面彈簧元的基本理論。對任何二維正交廣義彈簧系統，通過定義廣義彈簧變形與單元應變之間的關系，直接對比單元的應變能與彈簧系統的彈性勢能即可得到廣義彈簧剛度系數的表達形式。定義泊松剛度系數和純剪剛度系數兩個系統參數，描述正交廣義彈簧之間的聯系。對任意泊松比的材料，該方法都可準確地描述泊松效應的影響，計算結果與傳統有限元法一致。該方法不需要求得有限元單元剛度矩陣的具體形式，具有直接方便、物理意義明確的優點，應用該方法給出任意4節點單元彈簧系統的構造形式及其各剛度系數的表達式。基于SEM的可變形塊體離散元法，用彈簧元中的廣義彈簧求解塊體變形，用離散元中的接觸彈簧計算塊體間作用力，在單元節點的控制方程中實現彈簧元-離散元耦合計算，通過接觸彈簧的狀態實現材料由連續到非連續的破壞過程。在基于連續介質離散元法（CDEM）程序的基礎上實現了彈簧元-離散元耦合程序，應用耦合程序計算了均質土坡在重力作用下的彈塑性變形和基覆邊坡在重力作用下的破壞，初步證明該方法用于邊坡變形漸進破壞分析的可行性。

關鍵詞：彈簧元法 離散元法 彈簧剛度 邊坡工程

Abstract：Aiming at the continuous-discontinuous failure process of rock and soil materials in slope engineering，a novel deformable block discrete element method which combined spring element method（SEM） and discrete element method（DEM）together is presented. Compared with the accustomed element in traditional finite element method（FEM），the element in SEM is described as a spring system that contained some orthogonal generalized springs.This generalized springs are defined in 3D space， which means that each spring can has two or three spring stiffness.How to determine the generalized spring stiffness for continuous material is the difficult and most important in SEM.With the triangle element as an example，the basic theory of SEM is introduced in detail.Assuming the relationship between the generalized spring deformation and the element strain，the generalized spring stiffness can be obtained directly by comparing the elastic strain energy of the element and the elastic potential energy of the spring system.The Poisson and shear stiffness coefficients were defined as system parameters to describe the relationship between different generalized springs.The SEM can consider the Poisson effect accurately for any Poissons ratio material；and the result using SEM are the same with using traditional FEM.This method does not need to know the expression of the element-stiffness-matrix. It can be used in 4-node element；and the stiffness expressions of springs are given clearly. With the SEM used to compute the block deformation and the contact-spring used to calculate the interaction between blocks，the combined SEM/DEM program can be used to simulate the failure process of rock and soil material from continuous to discontinuous.The SEM and DEM are combined in the motion equation of each node in each element.The contact-spring in DEM satisfied specific strength criterion.When the contact-spring force exceeded its limit，the material became discontinuous from continuous. The combined SEM/DEM program is implemented easily in the continuum-based discrete element method（CDEM）program.The simulation of a homogeneous soil slope under gravity shows that the SEM is performed as good as FEM when using line elastic constitutive and reasonable when using Mohr-Coulomb strength criterion. The simulation of a bedrock and overburden layer slope shows that the combined program is suitable to simulate the slope failure process.

Key Words：Spring element method（SEM）；Discrete element method（DEM）；Spring stiffness；Slope engineering

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