基于变形数据分解处理的基坑危险性潜势分级研究

Hazard Potential Classification of Foundation Pit Based on Deformation Data Decomposition

为合理评价基坑在施工过程中的危险性潜势等级,以武汉洪山地铁站基坑变形监测成果为基础,通过改良的互补集成经验模态分解进行变形数据的分解处理,利用基坑变形的极限位移值和预警值构建相对判据,根据变形预测和M-K分析构建绝对量判据和趋势判据,以此进行基坑变形潜势分级。结合危险性分级结果和变形潜势分级结果,提出基坑安全施工的措施建议。实例分析表明:在变形数据的分解处理过程中,MCE-EMD模型较传统分解模型的优越性明显,所得评价指标g值为2.837,具有合理分解基坑变形数据的能力。在危险性分级过程中,危险性在现状分级条件下的相对判据指标F_(r)的变化范围为:0.58~0.72,预警等级处于Ⅰ~Ⅱ级;危险性在最终分级条件下的相对判据指标F_(r)的变化范围为:0.66~0.81,预警等级处于Ⅱ~Ⅲ级。在变形潜势分级过程中,绝对量判据和趋势判据条件下的潜势等级存在一定差异,且最终潜势等级的变化范围为Ⅰ~Ⅱ级。对比两类分级成果,按照不利原则,确定现状条件下的基坑危险性潜势等级相对较低,为Ⅱ级;但随着时间持续,危险性潜势等级具有升高的趋势,可升高至Ⅲ级。因此,有必要加强监测频率,以备不测。

In order to reasonably evaluate the hazard potential level of a foundation pit in construction process,this work utilized the decomposition of the improved complementary integrated empirical mode to decompose the deformation data based on the deformation monitoring results of the foundation pit of Wuhan Hongshan Subway Station.The relative criterion was constructed by using the limit displacement value and early warning value of the deformation of the foundation pit,and the absolute criterion and trend criterion were constructed by using the deformation prediction and M-K analysis.In combination with the risk classification and the deformation potential classification,the comprehensive measures and suggestions were proposed.The case analysis shows that,the MCE-EMD model has obvious advantages over the traditional decomposition model during the decomposition process of deformation data,and the obtained evaluation index g value was 2.837.This MCE-EMD model is confirmed to reasonably decompose the deformation data of the foundation pit.In the process of risk classification,the relative criterion index F_(r)of the risk varies in a range of 0.58~0.72 under the current classification conditions,and the early warning level is gradeⅠ~Ⅱ.Under final classification condition,the relative criterion index F r of the risk ranges in 0.66~0.81,and the early warning level is gradeⅡ~Ⅲ.In the process of deformation potential classification,there is a certain difference in the potential level,according to the conditions of absolute quantity criterion and trend criterion.The variation range of the final potential level is gradeⅠ~Ⅱ.The comparison of the two classification results suggests that the hazard potential level of the foundation pit is relatively low under the current condition on the basis of the adverse principle,and the level is grade II.However,the hazard potential level tends to increase over time,which can be raised to grade III.Therefore,it is necessary to increase the monitoring frequency in case of accidents.