承压富水砂土地层桩洞法施工变形控制研究

Study on the deformation control of PBA construction method in pressure water sand stratum

北京地铁7号线双井站位于繁华的CBD核心区,车站附近存在复杂的建筑群,同时地下存在密集的管线分布;双井车站地层为饱水的砂土互层地层,受施工扰动变形大.由于双井站工程特点复杂,对该车站砂土互层地层采用8导洞"桩洞法(PBA)"施工中地层的变形特点进行了数值模拟分析,探讨了"8导洞"中不同的开挖层序和8导洞不同的开挖次序引起的车站地层地表的沉降变形特点,分析了"8导洞PBA法"在扣拱、主体开挖及二次衬砌施工的不同施工阶段砂土互层地层变形的变化.基于"8导洞"施工模拟计算结果,考虑"群洞效应"影响,提出了"先下导后上导、导洞间相互交错"的导洞施工顺序;制定了同一层导洞错距10 m,上下层导洞错距15 m,以减少导洞间施工影响的工程措施.以上基于数值分析建议并实施的工程措施,满足了承压富水砂土地层"8导洞PBA法施工"地层变形控制的要求,指导了北京地铁7号线双井车站的施工,取得了良好的效果.

The Shuangjing station of Beijing Metro 7# line is located at core area of CBD, which is near the complex building group and exists intensive underground pipelines. The strata where the station is located at are saturated interbedded soil and sand, which would be deformed greatly under the construction disturbance. Because the project characteristic of Shuangjing station is complicated, this paper carried out numerical simulation for PBA method with 8 pilot tunnels of the station and analyzed the deformation properties of stata interbedded soil and sand in construction process. This paper also discussed the strata subsidence properties corresponding to different excavation sequence of layers and different excavation sequences of 8 pilot tunnels. Further more, analyzed the strata deformaton change during difference construction stages of ＂PBA method with 8 pilot tunnels＂ such as supporting arc, main body excavation and secondary lining. According to the result of simulation calculation and considering group tunnel effect in construction process, the study proposed the construction sequence of ＂ Lower pilot tunnel first and upper pilot tunnel second, and pilot tunnels staggered ＂.What is more, this paper put forward a construction measure that the distance between pilot tunnels in the same layer of 10 meters, and the distance between upper pilot tunnel and lower pilot tunnel of 15 meters, so as to effectively reduce the interaction between the pilot tunnels in construction process. The proposed measures based on the results of numerical analysis guided the project construction and got satisfied effect, which met the requirements of saturated stratum deformation control of ＂ PBA method with 8 pilot tunnels＂ of Shuangjing station.