上跨城轨段基坑开挖安全性模拟及施工控制

Safety Simulation and Construction Control of Foundation Pit Excavation in Overpass Metro

随着我国基建规模扩大,大量明挖基坑上跨既有地铁线路,基坑卸荷势必对下方地铁线路及支挡结构造成不利影响,评估基坑安全是施工面临的重要难题。文中以十字门隧道为依托,采用数值模拟的方法建立隧道-支护有限元模型,模拟隧道上浮量、管片裂缝和围护结构位移变形规律。研究结果表明:①珠机城轨结构上浮量及H形桩墙各个方向位移随基坑开挖深度加大而增加,但隧道竖向和水平位移均小于规范限值20 mm,隧道管片接缝张开量小于控制值3 mm;②基坑开挖后及时施做底板可有效阻止隧道管片上浮,且对管片有50%的回压作用;③采用MJS工法对坑底进行门式加固且分两仓开挖可有效控制坑底隆起。

With the expansion of infrastructure scale,there area large number of open-cut foundation pits crossing the existing subway.The unloading of foundation pits is bound to have a negative impact on the subway below and the retaining structure,therefore,the evaluation of foundation pit safety is an important problem in construction.Based on the cross gate tunnel,the finite element model of tunnel surrounding rock-support structure is established by using the method of numerical simulation,and the displacement and deformation laws of tunnel floating,segment cracks and envelope structure are simulated.The results are as follows:firstly,the floating capacity of Zhuji urban rail structure and the displacement of H-shaped pile wall in all directions increase with the increase of foundation pit excavation depth,but the vertical and horizontal displacement of the tunnel are both less than the standard limit of 20 mm,and the splaying amount of the tunnel segment joints is less than the control value of 2 mm;secondly,the timely application of bottom slab after pit excavation can effectively prevent tunnel segments from floating and has 50%back pressure effect on segments;lastly,the uplift of pit bottom can be effectively controlled by using MJS method with portal reinforcement and two layered block excavation.