The Working Performance Analysis For Steel Bracing Of The Deep Excavation Of Subway Stations

With the rapid development of urban construction, many cities have the rise of construction of the metro, and a large number of deep excavations also will be there. As an economical and effective way, the support pattern of cast-in-place pile and steel bracing has been widely used. Steel bracing system is a crucial component of the pile-strut bracing structure. If the design of steel bracing is not rational, the foundation pit will be dangerous.Relying on the Kaixuan Road station of subway line one in Zhengzhou, the article analyses that axial force of steel bracing is influenced by temperature and the stress of other steel supports when they are installed or removed.The main results are as follows:(1) Through the load and non-load test, the variation law of axial force is analysed with the change of temperature, and a connection is established between the two conditions.(2) As the upper surface temperature of steel bracing rise, axial force of the first layer support will increase 17kN/℃. It is the 1st, the 2nd and the 3rd tier bracing in order of size about the value which is affected by the temperature.(3) Eliminating the temperature factor, the amendatory rule of axial force is given. When foundation pit is excavated and steel supports are removed, the axial force will increase.But when steel supports are installed, the axial force will reduce.(4) In general, the loss rate of axial force is 10-50 percent when the temperature factor is eliminated. The greater prestress of steel support, the greater loss rate is.(5) Through the field experiment and analytical model, the two influenced range are analysed and the results are similar. When the influence value of the first layer support is calculated, the result should multiply by 0.3-0.5. And when the influence value between the first and the second layer support is calculated, the result should multiply by 0～0.8.(6) Because of prestressing loss, when steel supports are removed the influence to neighboring supports is less than that when installed. The range of influence depends on prestress and the rigidity and size of supporting structure.