全风化岩层中双线盾构上穿近邻地铁隧道影响分析

Analysis of double-line shield tunnel over-crossing subway tunnel in completely weathered rock formation

依托佛莞城际铁路盾构隧道在全风化花岗岩地层中上穿广州地铁七号线工程,针对全风化花岗岩地层致密、渗透系数小及双层四线叠交穿越复杂地层等特点,通过现场监测与三维动态有限元数值模拟手段,解决实际工程中注浆压力合理取值与既有隧道变形控制这两大难题。其中,通过模拟掘进隧道在不同注浆压力值的工况下,对既有隧道动态上浮变形值和地表沉降值的影响关系,进而确定最佳注浆压力值。同时,由于双层四线叠交穿越工况对既有隧道扰动的影响较大,为避免发生管片错台和开裂等危险,结合工程实际提出控制既有隧道变形的措施。研究结果表明:在全风化地层中注浆压力设为0.5MPa时,能合理控制地表沉降与既有隧道变形;穿越施工对既有地铁隧道竖向变形的影响存在"滞后效应";盾构单线穿越后,既有隧道竖向变形呈现近似单波峰状的正态分布曲线;盾构二次穿越后,曲线形态由近似正态分布曲线向类"M"双波峰形转变,且波峰位置产生约2m的偏移;既有隧道横断面管片最终变形呈"竖鸭蛋"状,其横向椭圆度为1.4‰,竖向椭圆度为0.71‰。针对分析结果,工程中采取合理的压重措施,有效抑制既有隧道的上浮变形,研究成果在隧道穿越类似地层的施工中具有一定的参考价值。

Based on the shield tunnel of Foguan Intercity Railway over-crossing Guangzhou Metro Line 7 in completely weathered granite formation, and considering the characteristics of completely weathered and dense granite formation, low permeability and over-crossing of two layers and four lines in complex stratum, the two challenges of reasonable value of grouting pressure and deformation control of existing tunnel encountered in practical projects were solved by means of field monitoring and three-dimensional dynamic finite element simulation. The optimal grouting pressure was determined by simulating the influences of different grouting pressures on the dynamic uplift deformation of existing tunnels and ground surface settlement. In addition, because the double-layer four-line overlapped crossing conditions had a greater impact on the disturbance of existing tunnels, the measures of controlling the deformation of existing tunnels were put forward in combination with engineering practice, in order to avoid the danger of segment dislocation and concrete cracking. The results show that when the grouting pressure of 0.5 MPa is set in the completely weathered rock stratum, the ground surface settlement and deformation of existing tunnels can be reasonably controlled;for the influence of crossing construction on the vertical deformation of existing metro tunnels, there is a "lag effect";after crossing of single-line shield tunnel, the vertical deformation of existing tunnels presents a normal distribution curve of single-peak wave shape;after the second crossing of shield tunnel, the curve shape changes from the normal distribution to the M-like double-peak wave shape, and the locations of the wave peaks have an offset of about 2 m. The eventual deformation of the cross-section of the existing tunnel segment appears to be "vertical duck egg" shape, with the transverse ellipticity of 1.4‰ and the vertical ellipticity of 0.71‰. Based on the analysis results, reasonable weighting measures were taken in the project, and the uplift deformation of the existing tunnel was effectively restrained. The research results can be referred by those projects with construction of crossing tunnels in similar strata.