上软下硬深基坑变形规律与空间效应分析

Research on Deformation and Spatial Effect of Upper-soft and Lower-hard Deep Foundation Pit

闽东南沿海广泛分布有滨海相、溺谷相沉积淤泥层,其一般下伏风化不均的花岗岩层,由此产生了大量的上软下硬的深基坑工程。但目前对上软下硬深基坑变形规律及其空间效应还缺乏系统深入的研究。以福建某医院综合楼上软下硬的深基坑支护工程为研究对象,通过追踪不同阶段不同测点的监测数据,对基坑开挖过程中的围护结构位移、支撑轴力、立柱隆沉、地表沉降进行了研究,并着重分析了其空间效应。研究结果表明:基坑浅层土体开挖时,对基坑围护结构及周边环境的影响较小,而当基坑中部淤泥软土层开挖时,则会引起基坑围护结构产生较大的侧移增量,其变形量约占最大侧移量的33%~60%;相较于常规软土基坑,上软下硬的深基坑最大侧移所处位置深度上移,最大侧移量减小,其更接近与常规基坑的下限值;基坑底板的及时施作能有效降低基坑的侧移变形、支撑的轴力、基坑底部的隆起以及对周边管线的影响;该类基坑亦存在显著的空间效应,表现为坑角附近围护结构的侧向位移、支撑轴力、周围管线及建筑沉降等显著小于基坑中部。

In the southeastern coastal areas of China,there are widely distributed upper-soft and lower-hard strata,resulting in a large number of upper-soft and lower-hard deep foundation pit.However,there is still no sufficient study on the deformation and spatial effect for the upper-soft and lower-hard deep foundation pit.Taking the upper-soft and lower-hard foundation pit supporting engineering in Fuzhou,by tracking the monitoring data of different measuring points in different stages,the displacement of the retaining structure and the supporting shaft during the excavation of the foundation pit were studied,and the spatial effects of the foundation pit were analyzed.The results show that the foundation pit shallow excavation has less impact on the foundation pit retaining structure and the surrounding environment.When the silt soft soil layer is excavated,the lateral deformation of the retaining structure will be increased,in which the deformation accounts for 33%~60%of the maximum lateral deformation displacement.Compared with the conventional foundation pit,the maximum lateral displacement position of the upper soft and hard deep foundation pit moves up,and the value of maximum lateral is reducing,which is closer to the lower limit of the conventional foundation pit.The timely application of the foundation pit can effectively reduce the lateral displacement deformation of the foundation pit and the influence on the surrounding pipeline.The spatial effect of the foundation pit is gradually weakened as it moves away from the foundation pit corner.This type of foundation pit also has significant spatial effects.The lateral displacement,supporting axial force,surrounding pipelines,and building settlements of the retaining structure near the corner of the pit are significantly smaller than those in the middle of the foundation pit.