柔性基坑支护体系的局限性与应对措施研究

Research on the Limitation of Flexible Foundation Pit Supporting System and Its Countermeasures

研究目的:本文以重庆市土岩组合地层中某地铁车站深基坑工程变形控制为例,对基坑变形原因进行分析,提出变形控制措施,进一步通过计算分析,得出基坑桩锚柔性支护体系在控制基坑大变形时的缺点,并明确桩锚撑组合支护体系的优势。研究结论:(1)基坑变形过大的原因可分为内因与外因两大类,其中地层软弱分界面倾向基坑侧、降雨导致分界面地层强度参数降低以及锚杆柔性支护体系控制变形能力较弱是基坑变形超限的内因,施工爆破、地表塔吊超载是基坑变形超限的外因;(2)基坑失稳在很大程度上取决于变形超限,而非围护结构强度破坏,实际工程中应加强变形监测与动态反馈;(3)桩锚体系下,锚杆作为一种柔性支撑结构对控制变形的继续发展作用有限,桩锚撑组合支护体系可有效地将原锚杆承担的荷载转移至内支撑,从而减小锚杆的拉力与变形,达到控制基坑稳定的目的;(4)该研究结论可为类似工程提供理论支撑与应用参考。

Research purposes： Based on the deformation control of a certain metro station in Chongqing in soil - rock composite stratum, the deformation reason and relevant countermeasures are put forward. Then, through numerical analysis, the defects of pile - anchor flexible retaining system are made clearly, and the advantage of composite retaining system of pile - anchor - strut is put forward. Research conclusions： （ 1 ） The excess deformation of foundation pit can be classified into internal and external factors. The internal factors include the interface of stratum inclining to foundation pit, the weaken of stratum interface because of rainfall, and the weak deformation control of flexible pile - anchor supporting system. The external factors include construction blast and overload due to tower crane on ground. （ 2 ） The failure of foundation pit is largely depended on excess deformation, rather than the strength failure of retaining structure. Deformation monitoring and dynamic feedback should be strengthened during construction. （ 3 ） As for the flexible pile - anchor retaining system, limited role for the control of continued deformation is found. The composite retaining system of pile - anchor - support can effectively reduce the tensile stress and deformation of anchor rod, and the stability of foundation pit can be realized research conclusions can provide some references for similar project in future. （4） The research conclusions can provide some references for similar project in future.