软土地区偏压基坑抗隆起稳定安全系数的强度折减法研究

Strength reduction method for safety coefficient of heave-resistant stability of asymmetrically-loaded excavations in soft soil areas

针对偏压工况下软土地区基坑开挖的坑底隆起问题,建立了二维有限元强度折减分析模型。对偏压范围、偏压距离以及偏压荷载大小对抗隆起稳定安全系数的影响进行了数值模拟分析,同时对比了极限平衡法、极限分析法和上述数值方法在偏压工况下的抗隆起稳定安全系数。结果表明:偏压范围越大或偏压距离越小,基坑抗隆起稳定安全系数越小;不同深宽比下的基坑抗隆起稳定安全系数均随偏压荷载大小增加而线性减小;Terzaghi极限平衡法和极限分析法均高估了偏压基坑的抗隆起稳定性,偏危险;Bjerrum&Eide极限平衡法和基于Prandtl机构的规范法低估了偏压基坑的抗隆起稳定性,偏保守。

A two-dimensional finite element model incorporating the strength reduction method is established to study the base heave problem encountered in asymmetrically-loaded excavations in soft soils.The parametric studies are conducted to investigate the influences of distribution range,distance from the bracing structures and amplitude of the asymmetric loading on the base-heave resistance factor.Meanwhile,comparisons are made among the above numerical results,the limit equilibrium method and the limit analysis method.The analysis results show that the heave-resistance factor decreases when the distribution range of the asymmetric loading increases or the distance between the asymmetric loading and the bracing structures decreases.The base-heave resistance factors of excavations with different depth/width ratios all show a linear decrease with the increasing amplitude of asymmetric loading.Compared to the strength reduction method,both the Terzaghi limit equilibrium method and the limit analysis method overestimate the base-heave resistance factor of an asymmetrically-loaded excavation,while both the Bjerrum&Eide limit equilibrium method and the code method(based on Prandtl mode)are conservative since they underestimate the factor.