基于鲁棒性原理的碎石桩置换率优化

Optimization of Area Replacement Ratio of Stone Column Based on Robustness Principle

碎石桩是处理软土地基的常用方法之一,置换率作为碎石桩设计中的关键参数,其值取决于软土力学参数和工后沉降量限值等要素。考虑实际工程中软土力学参数的不确定性,以及综合衡量工后沉降量和工程造价,确定最优置换率。本文首先基于岩土工程鲁棒性设计原理,将桩体压缩模量和土体压缩模量视为具有不确定性的参数即噪声因素,利用Monte-Carlo模拟方法生成噪声因素的数值,并基于单向分层总和法计算工后沉降量标准差作为鲁棒性指标,从鲁棒性、安全性和经济性3个方面优化碎石桩置换率;然后提出了碎石桩鲁棒性设计流程并通过工程案例说明其应用方法,基于此例讨论了沉降量限值、压缩模量变异系数和参数分布模式对优化结果的影响规律。结果表明:通过本文计算流程的最优置换率值为29%;沉降量限值的提高需要投入更多的工程造价;土体压缩模量相较于碎石桩对最终优化结果的影响幅度更大;相较于对数正态分布,采用正态分布模拟噪声因素参数分布时计算的结果不确定性更高。

Determination of the specific area replacement ratio is crucial in construction,considering the uncertainty of mechanical parameters of soft soil itself and the balance between post-construction settlement satisfaction and cost.Based on the robust geotechnical design principle,the pile and soil constrained modulus is regarded as noise factors with uncertainty,and by using the Monte-Carlo simulation method the value of several possible noise factors is determined;Further,the standard deviation of post-construction settlement is calculated by the one-way layer-wise summation method as the measure of robustness;Finally,the area replacement ratio of gravel pile could be optimized with considering safety,cost and robustness simultaneously.In this study,a robust design framework of stone column was proposed and its application was illustrated through an engineering example.Based on this example,the influence rules of settlement limit,coefficient of variation of compression modulus,and parameter distribution mode on the optimization were discussed.The results show that the optimal replacement rate is 29%;The improvement of settlement limit increases the engineering cost;The compressive modulus of soil has a greater influence on the final optimization than that of gravel pile;When using normal instead of lognormal distribution to simulate the noise factor distribution,the results of this calculation are more uncertain.