连拱隧道近接重叠既有隧道时的施工性态数值模拟

Numerical simulation and analysis of construction behavior for dual-arch tunnel tunneling overlapped to existing tunnel

以具有浅埋、偏压、近距离不对称重叠于下部既有小净距隧道等特征的雅山连拱隧道为工程背景,借助数值模拟手段,分析偏压近接重叠条件下连拱隧道正洞采用＂先深后浅＂及＂先浅后深＂两种开挖工序下的施工力学形态.通过比较两工序中连拱隧道围岩和既有小净距隧道衬砌的变形情况、中隔墙变位和受力情况,可知两开挖工序中,连拱隧道围岩变形基本一致,竖向沉降和水平位移值分别以右侧深埋正洞拱顶和浅埋左侧正洞与中导洞相交处为最大,其值分别达到3.19 mm和1.17 mm;浅埋偏压条件下,中隔墙自浇筑成型即处于小偏心受压,但其初始倾斜变位因正洞的开挖而逐步得到拨正;连拱隧道岩体开挖将导致既有小净距隧道内侧拱肩-拱腰区域衬砌出现朝向开挖区的变形,且＂先深后浅＂工序较＂先浅后深＂工序偏大0.01~0.02 mm.

Considering Yashan dual-arch tunnel with characteristics of shallow buried depth,unsymmetrical load and closely adjacent to an existing small-distance tunnel, the two construction processes of a dual-arch tunnel were simulated by FEM under the sequences of ″ deep to shallow″ and″shallow to deep″ to tunnel the main-hole respectively. The deformation stress condition of dual-arch tunnel surrounding rock and lining of existing small-distance tunnel and the displacement of middle-wall in the two tunneling sequences were analyzed and compared. The results indicate that the deformation rule of dual-arch tunnel in the two construction processes is basically consistent. The largest vault settlement occurs at the deeper buried main-hole,and the largest horizontal displacement appears at the junction of shallow buried left main-hole and middle-pilot with values of 3. 19 mm and 1. 17 mm,respectively. Due to unsymmetrical load, the middle-wall subjects to compression load with small eccentricity since it is completed. However,the initial deflection of middle-wall is corrected gradually when either main-hole is excavated. After rock mass excavation of the dual-arch tunnel,the small-distance tunnel lining between spandrel and haunch occurs displacement with moving toward the dual-arch tunnel,and the displacement of ″deep to shallow″ is 0. 01 ~ 0. 02 mm larger than that of ″shallow to deep″.