基于可拓云理论的泥炭质土场地沉降风险评价

为更好地研究泥炭质土场地地铁车站基坑周边沉降问题,预测和评估施工时及施工后的沉降风险,在分析了泥炭质土的特点后,选择土层厚度、有机质质量分数、重度、天然含水率、孔隙比、土层埋深和压缩模量7个指标,建立沉降风险评估指标体系,并根据改进层次分析法和改进熵权法求出主观权重与客观权重,最后用理想点法耦合主客观权重求出各评价指标的综合权重;根据沉降等级分类标准,生成每个评价指标的云滴图,计算得到各评价因子的可拓云矩阵,进而将综合权重向量与可拓云矩阵相乘得到综合确定度,根据综合确定度最大原则确定样本沉降风险等级。以昆明某地铁车站施工监测数据为例,用建立的可拓云模型对泥炭质土场地的沉降风险进行评价,最终评价结果与实际监测结果吻合较好,验证了分析方法的合理性及可行性。该评价方法充分考虑了多种因素影响,明确了沉降的风险等级,评价结果为泥炭土场地上建(构)筑物的设计施工及应急处理提供了理论依据。

Risk assessment of the settlement of peat soil field based on the extension cloud theory

The paper is aimed at making an evaluation of the construction risk and post-construction sub-sided settlement so as to explore the settlement regularity around the foundation pits of the subway station in the peat soil field. As a matter of fact,7 evaluation indexes have to be assessed and analyzed involving the analysis of the sedimentation features of the peat soil,which may include the soil thickness, the organic compositional content rates,the gravity,the natural water content rate,the void ratio,the soil depth,as well as the compressive modulus so as to establish the index system of the sedimentation influential factors according to the improved analytic hierarchical procedure,so as for the analytic method and the improved entropy weight method to be used to gain the subjective and objective weights. And,finally,the idealistic point method can be adopted to join up the subjective and objective weights to obtain the comprehensive weight of each evaluation index. And,then,it would be possible to summarize the cloud drop graph of each evaluation index in accordance with the classification standard of the settlement level,and then to calculate and work out the degree of certainty corresponding to each evaluation index,and the extension cloud matrix is composed of all the certain degrees. Afterwards,it would be possible to multiply the comprehensive weight vectors by the extended cloud matrix to obtain the comprehensive certainty in accordance with the comprehensive determination degree. The above said principle can thus identify and determine the risk level of the sample settlement by taking the construction monitoring data of a subway station in Kunming as a case study sample,with the settlement risk level of the peat soil site being established on the basis of the extension cloud model theory. The final evaluation results we have gained prove well in accord with the actual monitoring results,which can verify the rationality and feasibility of the analysis method. What is more,the evaluation method has full considered the impacts of the various factors by clarifying the risk level settlement. Thus,it can be said that the evaluation results provide a theoretical analysis basis for structures’ design,construction and the emergency on the peat soil site.