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采用有限单元法计算砂性土中的开挖卸载,根据既有的散粒体材料开挖应力释放和弹塑性卸载理论研究成果,将卸载过程中材料荷载–位移曲线的非线性等效成为开挖荷载的逐步释放,该过程中卸荷模量与加载模量一致。在此基础上,推导用卸荷刚度表示的计算域内开挖荷载计算式;同时,根据现有试验结果,将八面体剪应力引入以表征单次加卸载情况下颗粒间的摩擦作用力,并利用虚功原理建立颗粒间摩擦作用与卸载应力释放特性的关系,将应力释放效应对开挖荷载的影响等效成为修正开挖卸载阶段材料的弹塑性本构关系矩阵,从而实现考虑卸载摩擦效应的开挖问题计算方法。从节点平衡方程的推导来看,开挖荷载对整个计算区域均有影响,和应力释放效应存在对应关系。设计砂的室内单向加卸载模型试验,并采用该有限元方法对室内模型试验进行模拟,结果表明,单次加卸载过程中,计算曲线可以较好地反映对应试验条件下土体的应力释放特性,计算结果与现有的理论研究成果相符,该方法对开挖问题的描述具有一定的可行性。
The finite element method is used to calculate the excavation unloading in sand soil. Based on the existing research results of stress release and elasto-plastic unloading theory of loose aggregate material, the nonlinear equivalent of material load-displacement curve in unloading process is turned on Excavation of the gradual release of the load, the process of unloading modulus and load modulus. On this basis, the formula for calculating the excavation load in the calculation domain deduced by the unloading stiffness is deduced. At the same time, according to the existing test results, the octahedral shear stress is introduced to characterize the frictional force between the particles in the case of single loading and unloading By using the principle of virtual work, the relationship between the interfacial friction and the unloading stress release is established. The effect of stress release on the excavation load is equivalent to the elasto-plastic constitutive relation matrix of the material in the unloading phase of excavation, so that the unloading friction effect Excavation problem calculation method. According to the derivation of node equilibrium equation, the excavation load affects the whole calculation area and has the corresponding relationship with the stress release effect. The indoor unidirectional loading and unloading model test of sand was designed and the indoor model test was simulated by the finite element method. The results show that the calculated curve can well reflect the stress release of soil under the corresponding test conditions The characteristics and the calculation results are consistent with the existing theoretical research results. This method is feasible to describe the excavation problem.