基于主成分分析的基坑开挖对周边建筑物影响分析

Analysis on Influence on Surrounding Buildings by Deep Foundation Pit Excavating Based on Principal Component Analysis

富水砂卵石地层由于其高渗透性、低黏聚力、松散的结构等特点,给地铁深基坑工程施工带来了极大的难度,尤其是周边有临近建筑物、河道以及既有地铁线路时,对基坑施工技术提出了非常高的要求。依托成都地铁17号线凤溪站深基坑工程,针对富水砂卵石地层中基坑降水开挖对周边建筑物的影响规律进行了研究。通过Midas-GTS/NX有限元数值模拟结合实际工程监测数据对建构筑物的沉降随深基坑降水开挖的变化规律进行了分析,并采用主成分分析法计算了各监测指标对基坑稳定性评判的影响,得出结论:建立的有限元模型的预测结果略大于实际变形值,在富水砂卵石地层中进行降水开挖对周边环境的影响十分显著,随着开挖深度的增加,建筑物沉降、地表沉降均随之增大,在架设内支撑后,沉降随即趋于稳定,少数部位甚至会有微小的隆起;地面最大沉降出现在距离基坑边缘水平位置1/5开挖深度处,而临近河道一侧由于受到地下水的影响其沉降值相对较大;在基坑监测指标中,测斜与桩顶变形对基坑稳定性评价的贡献率最大,其次是地下水位、内支撑轴力以及地表沉降,可见测斜和桩顶变形反映了基坑降水开挖的稳定与否,在实际工程中应密切监测。

Due to the characteristics of high permeability,low cohesion and loose structure in stratum of water-rich and sandy cobble,the construction of deep foundation pit engineering of subway is very difficult.Especially when there are buildings,rivers and existing subway lines nearby,it is quite high requirement on the construction technology.Based on the deep foundation pit engineering of Fengxi Station of Chengdu Subway Line 17,the influence on surrounding buildings by dewatering and excavating of foundation pit in stratum of water-rich and sandy cobble is studied.Combing numerical simulation by Midas GTS/NX finite element with actual monitoring data,the variation of building settlements which are varying with dewatering and excavating of foundation pit is analyzed,and the influence of each monitoring indicators on the stability evaluation is calculated by the principal component analysis.It draws the conclusion that the predicted results of the established model are slightly greater than the actual deformations,and the influence that dewatering and excavating on the surroundings in stratum of water-rich and sandy cobble is very significant.As the depth of excavation increases,both buildings settlements and subsidence increase,and tend to stabilize after the inner support is erected,while a few parts may even uplift a little.The maximum subsidence occurs at a position where is from the edge of the foundation pit that equals the depth of 1/5 of the excavation,while the subsidence close to river is relatively greater because of the influence of groundwater.In the monitoring indicators of foundation pit,the contributions of inclination measurement and deformation on the top of the pile to the evaluation on stability of foundation pit are the highest,and the groundwater,inner support and subsidence following.It can be seen that the inclination measurement and deformation on the top of pile reflect the stability of dewatering and excavating,and should be monitored frequently in practical engineering.