既有地下结构受下穿施工影响的力学响应与安全控制研究

Safety control and mechanical response of existing underground structures induced by excavation of new tunnels under construction

北京地区下穿工程中,新建隧道断面及施工方法种类众多、地层条件复杂、既有结构形式多样,有极其复杂的组合关系,目前尚无对既有结构力学响应的系统分析。通过北京地区13个下穿工程案例,总结了新建隧道结构形式及施工措施,明确既有地下结构变形特点,采用两阶段法分析及预测了各因素影响下既有地下结构的力学响应。研究表明:(1)新建隧道包括市政管道、地铁区间及车站,常见的施工方法有多导洞法、台阶法,洞桩托换法和中洞法,新建隧道开挖面积与施工方法有较明确的对应关系。(2)既有地下结构实测最大沉降概率分布符合数学期望4.89,方差16.4的正态分布。其中,新建市政管道、地铁区间和地铁车站下穿施工引起的既有地下结构平均最大沉降分别为2.56,3.82,11.07 mm。(3)根据新旧隧道空间位置关系的不同,穿越工程可分为7种组合,其中,既有地下结构力学响应有V,U,W 3种模式。(4)严格控制新建隧道开挖面积,不留或少留间隔土,尽可能选择W型穿越模式,以此减小对既有地下结构的扰动。

In crossing projects,the sections and construction methods for new tunnels are numerous,the geological conditions are complex,and the structural forms of the existing tunnels are various.There is a complex relationship among them,which has not been deeply studied till today.Based on the measured data from 13 projects in Beijing,the structural forms and the construction methods for the new tunnels are summarized,the deformation laws of the existing tunnels are analyzed,and the mechanical response of the existing tunnels is investigated by using the two stage method.The results show:(1)The new tunnels have three types of municipal pipelines,subway stations and metro tunnels.Their construction methods include guiding hole method,bench method,cavern-pile method and center drift method.The corresponding relationship between the construction methods and the excavation area is clear.(2)The probability distribution of the maximum settlement of the existing tunnels accords with the normal one,with the mathematical expectation being 4.89 and the variance 16.4.The average maximum settlements of the existing tunnels caused by excavation of municipal pipelines,metro tunnels and subway stations are 2.56,3.82 and 11.07 mm.(3)The crossing projects can be summarized into 7 combinations by the spatial relationship between the new and existing tunnels.According to the deformation and stress characteristics,there are three modes of W,U and V in the mechanical response of the existing tunnels.(4)In order to reduce the disturbance of the existing tunnels,the excavation area of the new tunnels should be strictly controlled,the soil between the roof of the new tunnels and the floor of the existing tunnels should be less or not left,and the preferable crossing mode should be W-type.