邓肯-张模型应用于基坑工程中值得注意的问题

Noticeable problems of Duncan-Chang model applied in engineering of foundation pit

指出邓肯-张模型应用于基坑开挖和支护工程中值得注意的若干问题.针对一算例采用实体单元和结构单元相耦合的有限元法进行了数值模拟分析,分析过程中分别采用了现行单应力和双应力状态变量的加卸载准则.结果表明,由于二者加卸载判断上的差异,计算所得围护墙的位移和弯矩相差较大.数值模拟还揭示,作用在围护墙上的土压力是随基坑开挖和支护工况的变化而变化的,常可能大于主动土压力,因而支护结构的实际内力可能大于传统的按主动土压力作用所计算的内力,以致可能引起支护结构的强度破坏.

Several noticeable problems of Duncan-Chang model applied in excavation and retaining engineering of foundation pits were pointed out.An example of the finite element analysis was performed by coupling solid element and structural element.The existing loading-unloading criterions i.e.,the single stress state variable criterion and the double stress state variable criterion were adopted during the analyzing.The result showed that because of the difference of the judgments of loading-unloading,the calculated displacements and bending moments of the retaining structures by the two criterions were rather different.The numerical simulation also showed that the earth pressures acting on the retaining walls changed with excavation and brace setting,and may be greater than the active earth pressures.So the actual internal forces of retaining structures may be greater than those of calculated by the traditional active earth pressures.And the retaining structures may lead to be destroyed.