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为研究浅埋隧道掌子面稳定性及获取精细化的破坏模式,提出了一种上限有限元非结构化网格自适应加密策略。以单元耗散能权重指标作为网格自适应加密评判准则,该策略同时兼顾了单元尺度与塑性应变。应用高阶的6节点三角形单元并建立上限有限元线性规划模型,以多次反复计算和网格加密的方式实现了二维自适应上限有限元分析并编制了计算程序。利用条形基础地基极限承载力课题,从上限解精度和网格加密形态方面验证了该程序的有效性。针对浅埋隧道掌子面稳定性问题,展开多参数条件下的自适应上限有限元计算,分析了网格加密过程中单元总数与上限解精度的关系,列出不同隧道埋深和内摩擦角对应的隧道掌子面稳定性临界值的上限解,揭示出掌子面稳定性变化规律及精细化的破坏模式。
In order to study the stability of the face surface of shallow tunnel and to obtain the refined failure mode, an upper limit finite element unstructured grid adaptive encryption strategy is proposed. The weight dissipation index of the unit is taken as the criterion of grid adaptive encryption. This strategy takes into account both the cell scale and the plastic strain. A high-order 6-node triangular element is established and a finite element linear programming model of upper bound is established. The two-dimensional adaptive upper bound finite element analysis is realized and the calculation procedure is established by repeated calculation and grid encryption. Based on the research on the ultimate bearing capacity of strip foundation, the validity of the program is verified from upper bound solution and mesh encryption. In order to solve the problem of face stability of shallow tunnel, the finite element method of adaptive upper bound under multi-parameter conditions was developed. The relationship between the total number of cells and the upper limit solution accuracy was analyzed, and the depth of buried tunnel and internal friction angle Corresponding to the upper limit solution of the stability threshold value of the tunnel face, it reveals the changing rule of the stability of the face and the elaborate failure mode.