软土参数反分析方法及其在沉降预测中的应用

沉降预测与控制是当前客运专线设计、施工组织的关键技术,为保证沉降预测的准确程度,必须合理选取计算参数。采用黏弹塑(西原)模型模拟土骨架,并结合软土变形的大位移、大应变及渗透固结的特点,建立模拟施工过程的软土路基双重非线性固结分析有限元模型。以实测信息与计算信息的相对残差平方和最小为目标,引入考虑测点观测精度的加权值,建立根据多种测试信息进行参数反分析的目标函数,并采用Monte-Carlo法和可变容差法相结合的优化技术,对目标函数进行约束优化,较好地解决了可变容差法易于陷入局部最优解的难题。通过参数分组、初步试算、综合调整等步骤,建立了分阶段多层次动态施工反分析方法,从而使反分析所得计算参数具有明确的物理意义。实际工程应用表明,参数反分析方法本构关系清楚、物理意义明确,所得计算参数能较好地反映现场的实际情况,可准确预测沉降。

Back-Analysis Method of Soft Soil Parameters and Its Application in Settlement Prediction

Settlement prediction and control is the key technology in the design and construction organization of current passenger dedicated line.To ensure the settlement is predicted accurately,it is necessary to adopt reasonably the calculating parameters.For this purpose,double non-linear consolidation finite elements method analysis model simulating the construction process of embankment on soft soil ground was established,in which the soil skeleton was simulated by visco-elastic-plastic model,and some deformation characteristics of soft soil such as large displacement,large strain,permeability and consolidation were taken into account.Then the objective function that suitable for multi-information monitored was found,which based on the objective to minimize the sum of square of relative residual between the calculated information and the monitored one,and the weight value that concerned the monitoring precision on every monitored point was introduced into it.In order to settle the puzzle that the flexible tolerance method is liable to result in local optimum solution,the constraint optimization method synthesizing the flexible tolerance method and the Monte-Carlo method was developed.By means of the steps that parameters grouping,trial calculating and general adjustment,the stages multi-level dynamic construction back analysis method was set up,which ensures the obtained parameters possess specific physical meaning.All these above were applied to a practical expressway project.It indicates that the parameters obtaining from the back-analysis method established in this paper are capable of reflecting comprehensively the condition on site and predicting well the settlement of embankment.