盾构隧道近接浅埋式矩形隧道合理净距的研究

以正在建设中的深圳地铁11号线南山至前海湾站小净距重叠区间隧道为研究对象,按先明挖修建桂庙路矩形闭合框架隧道,后进行地铁盾构推进的顺序,采用FLAC有限差分程序对小净距重叠隧道进行弹塑性分析,对多种工况下的围岩位移、夹岩应力、塑性区分布等进行分析,提出矩形闭合框架隧道的管幕作用,其作用影响范围大致沿Mohr-Coulomb模型剪切破坏面(45°+φ/2)的角度,以矩形隧道宽为底边的闭合等腰三角形区域。在此区域内的地下结构均受管幕作用的影响,且距离矩形闭合框架隧道越近管幕作用越明显,在综合考虑了矩形隧道管幕作用和隧道之间近接效应的情况下,确定隧道之间的合理净距。

Study on Reasonable Clear Distance for a Shield Tunnel's Excavation Closely Adjacent to a Shallowly-buried Rectangular Tunnel

In this paper,the two overlapped tunnels with short clear distance on Nanshan-Qianhaiwan section of Shenzhen Metro Line Eleven were taken as research object. The two tunnels would be respectively excavated in the order: excavating the rectangular enclosed-frame tunnel along the Guimiao Road by open-cut method first and then excavating the shield tunnel. By using finite difference software FLAC,the elastic-plastic analysis of the overlapped tunnels with short clear distance was carried out under multiple working conditions,including the displacement of the surrounding rock,the stress of the shared rock,the distribution of plastic zone and so on. On this basis,the paper suggested that: there was a tube screen effect in the rectangular enclosed-frame tunnel; and the sphere of the tube screen effect was approximately along a( 45°+φ /2) angle of the shearing failure plane of Mohr-Coulomb model,within the range of a enclosed isosceles triangular of which the bottom edge was equal to the width of the rectangular tunnel. The paper also suggested that all the underground structures within above-mentioned range would be influenced by the tube screen; the closer the distance to the rectangular enclosed-frame tunnel,the more obvious the action effect would become. After fully considering the tube screen effect of rectangular tunnel as well as considering the proximity effect of adjacent excavation,the reasonable clear distance between the two tunnels has eventually been determined.