考虑多失效模式的桩-土结构体系稳健性设计

Robust geotechnical design of soil-pile foundation system considering multiple failure modes

针对桩基础设计中岩土参数和荷载的不确定性,首先,提出考虑多失效模式的桩-土结构体系的稳健性设计(RGD)方法,综合分析单桩竖向承载能力极限状态(ULS)、竖向正常使用极限状态(SLS)、水平强度失效和水平变形失效4种失效模式;其次,采用蒙特卡罗模拟(MCS)法和点估计法(PEM)嵌套的方法计算桩-土结构体系的失效概率均值和标准差,以失效概率标准差作为衡量结构稳健性的指标;最后,以稳健性和经济成本作为优化目标,确定单桩的最优设计。结果表明:多失效模式下,不同的单桩设计尺寸,起决定作用的失效模式不同;随着单桩设计几何尺寸的增加,桩-土结构体系的主控失效模式逐渐由桩水平强度控制转为由竖向正常使用极限状态控制;主控失效模式的变化,对结构体系的失效概率变化梯度影响较大。

In order to address uncertainties of geotechnical parameters and loads in pile foundation design,firstly,a RGD method considering multiple failure modes was proposed.Four typical failure modes,vertical ultimate limit state(ULS),vertical serviceability limit state(SLS),horizontal strength failure and horizontal deformation failure were analyzed.Then,Monte Carlo simulation(MCS)and point estimate method(PEM)nesting were adopted to compute mean value and standard deviation of failure probability for soil-pile foundation system,and the latter was used as an indicator to measure robustness.Finally,optimal design of soil-pile foundation system was finalized with robustness and cost as objectives.The results show that piles with different geometries have different dominant failure modes.With the increase of geometries,key failure mode changes from horizontal strength failure to vertical SLS,which has significant influence on gradient of of system’failure probability.