软土地区深基坑围护结构综合刚度研究

为了预测地铁深基坑开挖阶段围护结构的变形特性，从围护结构综合刚度的角度研究了软土地区地铁深基坑的围护结构设计方法。鉴于Clough综合刚度模型存在诸多缺陷，提出了新的MVSS综合刚度模型，其包含了围护墙（桩）刚度、基坑深度、支撑刚度、支撑水平及竖向间距、地基加固等多个变量，反映了基坑围护结构的整体属性。从有限元计算及地铁基坑实测变形等角度验证了MVSS综合刚度合理性，并建立了地铁深基坑围护结构侧向变形与基坑围护综合刚度之间的函数算式。该算式为基坑围护结构的变形预测提供了新的思路与方法。基坑围护结构最大侧向变形与基坑MVSS综合刚度呈递减函数关系，但当其MVSS综合刚度增大至一定程度后，其继续增大对基坑围护结构变形的进一步控制效果甚微。

A new system stiffness of retaining structure of deep foundation pit in soft soil area

In order to predict the deformation characteristics of retaining structure in deep foundation pit excavation, we study the design method of subway station excavation retaining structure in soft soil foundation pit from a retaining structure’ system stiffness point of view. A new concept of system stiffness, i.e. multiple variables system stiffness (MVSS) is proposed in view of the defects of Clough composite stiffness model. In addition to the stiffness of the retaining wall and the vertical spacing between the supports, as included in the original Clough model, several important parameters are introduced in the proposed MVSS model, including the depth of the foundation pit, the bracing stiffness, the horizontal spacing between the supports, basement reinforcement. Finite element method is employed to calculate the maximal lateral displacement of the retaining structure. The results show that the proposed MVSS model can describe excellently the deformation of the retaining structure. The measured displacement data from several foundation pits also validates the applicability of proposed method. Therefore, the proposed model is a liable and valuable way to determine the system stiffness of the deep foundation pit of subway in different strata. There exists a negative correlation between retaining structure of foundation pit and maximum lateral deformation, excavation MVSS comprehensive stiffness, but when the MVSS comprehensive stiffness increases up to a certain degree, the continued increase of MVSS comprehensive stiffness has an insignificant effect on controlling further the deformation of the retaining structure of foundation pit.