基坑支护结构的综合选型及受力与变形特性

Comprehensive Selection of Foundation Pit Supporting Structure and Behavior of Stress and Deformation

以京沪高速改扩建工程莱芜至临沂段一标段3#钢筋加工场深基坑工程为依托,采用多目标层次分析和模糊综合评判法选出适合本工程的支护形式。结合现场监测和数值模拟,分析在该支护形式下,基坑施工过程中的土体和支护结构力学及变形特征。采用基于多目标层次分析法(analytic hierarchy process,AHP)的模糊综合评判方法建立多指标评价体系,确定基坑支护采用上部1∶1放坡+土钉支护,下部咬合桩+钢筋混凝土内支撑的方案。研究结果表明:土体地表沉降随距基坑的距离呈先减小后增大的趋势,咬合桩能较好地控制边坡变形;咬合桩桩身最大位移位置随开挖的进行逐渐下移,且两次竖直位移的增量比约为相邻土层厚度比;受自重影响,咬合桩桩身弯矩对称,每条边中点附近弯矩值偏大。将现场监测结果与有限元分析数据结果进行对比,验证了数值模拟和多指标评价体系的可靠性。

The deep foundation pit project of No.3 section in 1 st section of Laiwu to Linyi section in Beijing-Shanghai Expressway Reconstruction and Expansion Project was taken into research.Both multi-objective level analysis and fuzzy comprehensive evaluation method were used to select the suitable support form for this project.Combined with on-site monitoring and numerical simulation,the mechanic and deformation characteristic of soil and supporting structure during the foundation pit construction of were analyzed when using supporting form.The multi-objective fuzzy comprehensive evaluation method based on multi-objective analytic hierarchy process(AHP)was used to establish a multi-index evaluation system,and upper 1∶1 slope+soil nail support method was determined.The research results show that the surface settlement decreases first and then increases with increase of distance from foundation pit.The bite pile can better control slope deformation well.The maximum displacement position of bite pile body gradually moves down with the excavation,and the ratio of two vertical displacements is equal to the thickness ratio of adjacent soil layer.Comparing the result of on-site monitoring result with finite element analysis data,the reliability of numerical simulation and multi-index evaluation system is verified.