典型软土地层管廊基坑垫层换撑可行性研究

Feasibility study on cushion replacement support for pipe gallery foundation pit in typical soft soil strata

针对基坑传统换撑方法换撑工序复杂,对管廊结构施工延续性及施工效率影响较大的问题,基于典型软土地层,以广东中山某管廊深基坑工程为背景,提出了利用垫层换撑的新方法.首先,对基坑进行三维Abaqus数值模拟并与实测数据进行对比分析;然后,提出垫层换撑方法并进行数值模拟正交试验,探究采用垫层换撑方法在拆撑后不同因素对基坑围护结构变形影响情况;最后,通过现场试验验证管廊深基坑垫层换撑新方法的合理性和可行性,并将垫层换撑方法与传统换撑方法对于围护结构水平位移影响进行对比.研究结果表明:影响围护结构变形的3个主要因素为垫层改良区域(垫层梁)厚度、混凝土强度等级和纵向钢筋直径,其中垫层改良区域(垫层梁)的厚度极差最大,为影响围护结构变形最显著的因素;垫层换撑现场实验在拆除底部横撑后,围护结构最大水平位移平均实测值仅为21.79 mm,有效解决了软土区围护结构易变形过大的问题,验证了垫层换撑方法的适用性;在基坑地层及开挖条件相同情况下,采用垫层换撑方法围护结构最大水平位移约为传统方法的84%,相较于传统换撑方法能够更好地控制基坑变形.

This study addresses the complexities and inefficiencies associated with traditional support replacement methods,specifically their impact on construction continuity and the efficiency of pipe gallery structures.A new method using cushion replacement support is proposed,based on the typical soft soil strata and a case study of a deep foundation pit project for a pipe gallery in Zhongshan,Guangdong.Firstly,a three-dimensional Abaqus numerical simulation of the foundation pit is conducted and compared with measured data for analysis.Then,the cushion replacement support method is proposed,and numerical simulation orthogonal experiments are conducted to explore the influence of different factors on the deformation of the foundation pit enclosure structure after support removal.Finally,the feasibility and rationality of the proposed cushion replacement support method are verified through on-site experiments,and its impact on the horizontal displacement of the retaining structure is compared to that of traditional methods.The research results indicate that the three main factors influence the deformation of the retaining structure:the thickness of the improved cushion(cushion beam),the strength grade of the concrete,and the diameter of the longitudinal steel bars.Among these,the thickness of the improved cushion(cushion beam)has the largest range,serving as the most significant factor affecting the deformation of the retaining structure.The on-site experiment of the cushion replacement support method shows that the average measured maximum horizontal displacement of the retaining structure is only 21.79 mm after the removal of the bottom horizontal brace.This effectively solves the issue of excessive deformation in soft soil areas and confirms the applicability of the cushion replacement support method.Under the same geological and excavation conditions in the foundation pit,the maximum horizontal displacement of the retaining structure using the cushion replacement support method is about 84%of that using the traditional method,demonstrating better control over deformation of the foundation pit compared to traditional support replacement methods.