不对称深基坑变形性状现场监测分析

Field monitoring on deformation behavior of non-symmetrical foundation pit

目前城市地下已预埋大量变形敏感结构,基坑设计准则从稳定控制转为变形控制。基坑的变形性状与其三维构型密切相关,现有研究常假设基坑是对称结构,而实际工程中基坑常因具有附属结构而表现出非对称性。目前仍缺乏关于非对称基坑三维变形性状的深入认识,相关现场数据也少有报道。为研究软土地区两侧支护形式不同的非对称基坑开挖过程中的变形规律,现场实测了绍兴市轨道交通1号线非对称狭长深基坑在开挖过程中的墙体变形和坑外地表沉降。分析发现:(1)基坑附属结构的存在使得围护结构的侧向位移及地表沉降与未加强侧变形差距达20%;(2)基坑墙体测斜、坑外地表沉降沿狭长基坑方向的分布与附属结构关联不大,近似遵循互补误差函数(erfc);(3)软土地基中设附属结构可以显著控制基坑变形。本项目监测分析可为软土地区不对称深基坑设计与施工提供借鉴。

A large number of deformation-sensitive structures have been pre-buried underground in urban areas,shifting the criteria for foundation pit design from stability control to deformation control.The deformation behavior of foundation pits is closely related to their three-dimensional configuration.Previous studies often assume that foundation pits are symmetrical structures,whereas in actual engineering,foundation pits often exhibit non-symmetry due to the presence of auxiliary structures.Currently,there is still a lack of in-depth understanding of the three-dimensional deformation behavior of non-symmetrical foundation pits,and there are few reports on related field results.In order to study the deformation behavior during the excavation process of non-symmetrical foundation pits with different supporting forms on both sides in soft soil areas,wall inclinometer measurements and surface settlement outside the foundation pit were measured on-site for the narrow and long deep foundation pit of Shaoxing Metro Line 1.The results show that the presence of auxiliary structures in the foundation pit leads to a discrepancy of up to 20%between the lateral displacement of the retaining structure and surface settlement compared to unreinforced side.The distribution of lateral displacement and the surface settlement is not strongly correlated with auxiliary structures,but approximately follows the complementary error function(erfc).The auxiliary structures in soft soil foundations can significantly control the foundation pit deformation.The conclusions drawn can provide guidance for the design and construction of non-symmetrical deep foundation pits in soft soil areas.