预应力控制大基坑中的水平位移

Research of Displacement Control with Prestress in Long Excavations

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,the width of excavations is getting more and more in China. When the minimum width is close to 100 meters,the supporting stiffness falls sharply and temperature effect rises obviously. It is very difficult for conventional steel support or concrete support to ensure the displacement of excavation under the control. An innovative prestressed support system could limit the displacement of excavation within 30 mm. The Innovative Prestressed Support System is a perfect solution to control the displacement. There are two keys to ensure prestressed support success.( 1) Prestressed working mechanism: the prestress is able to control displacement if the passive earth pressure is born with the increasing of prestress.( 2) In calculation of the stability of brace more than 100 m long with considering the lateral restraint by the column,there's no need to calculate the stability of brace as a whole.