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目前我国的基坑越来越大。当最小宽度接近100 m时,内支撑刚度急剧下降,温度影响明显上升,常规的钢支撑或混凝土支撑都很难将基坑坑壁水平位移控制在规范的要求之内。预应力支撑能将这种超大基坑的水平位移控制在30 mm以内,是针对大基坑的最佳内支撑形式。本文论述了预应力支撑在大基坑中应用时必须要解决的两个基本概念和计算理论问题:(1)在下层土体开挖前,采用预应力将坑壁外的被动土压力充分激发出来。才能有效地起减小位移的作用;(2)100 m的超长对撑若考虑了支撑的立柱对支撑的侧向弹性约束,就可以不必进行整体稳定验算及相应的强度削减。
At present, China’s foundation pit is growing. When the minimum width is close to 100 m, the stiffness of the inner support drops sharply and the temperature effect obviously increases. It is difficult for the conventional steel support or concrete support to control the horizontal displacement of the foundation pit wall within the requirements of the specification. Prestressed support can control the horizontal displacement of this kind of large-scale foundation pit within 30 mm, which is the best internal support for large foundation pit. This paper discusses two basic concepts and computational problems that must be solved in the application of prestressed bracing in large excavation: (1) Before the excavation of the lower soil, the passive earth pressure outside the pit wall is fully excited by the prestress come out. Can effectively reduce the displacement of the role; (2) 100 m of the long support If the support column to consider the lateral elastic constraint, you can not need to conduct an overall stability check and the corresponding strength reduction.