高地应力蚀变花岗岩隧道大变形特征及成因分析

Large Deformation Characteristics and Genetic Analysis of High Geostress Altered Granite Tunnel

西部山区某蚀变花岗岩隧道施工过程中,围岩大变形不同程度地造成喷射混凝土剥落、钢架扭曲变形、钢拱架断裂、初支变形侵限以及隧道内坍塌等。为揭示蚀变花岗岩隧道围岩大变形的孕育机理,通过岩石试验、监控量测、数值计算分析和地质综合分析等多种方法,对蚀变花岗岩隧道高地应力及大变形特征、影响因素进行探讨分析。蚀变花岗岩隧道工程区受构造影响强烈,蚀变特征显著,岩体结构疏松,蚀变花岗岩地层为大变形提供充足的物源条件。隧道现场监控量测显示发生大变形的蚀变花岗岩区段与地下水紧密相关,蚀变花岗岩中的伊蒙混石、绿泥石等亲水性矿物成分含量较高,遇水极易崩解,使得岩体抵抗变形的能力大幅降低。结合隧道地质条件和地应力测试,反演分析了隧道初始地应力场,发现蚀变花岗岩隧道以水平构造应力为主,隧道沿线多处于高地应力状态,为大变形的发生提供内动力地质条件。根据隧道开挖过程中发生的支护变形及监控量测分析,复杂地质条件对隧道设计的影响以及施工工艺与支护结构的质量是引起围岩大变形的重要主观因素。

During the construction of an altered granite tunnel in the western mountainous area,the large deformation of surrounding rock causes shotcrete spalling,steel frame distortion,steel arch fracture,initial support deformation intrusion and tunnel collapse to varying degrees.In order to reveal the inoculation mechanism of large deformation of surrounding rock of altered granite tunnel,the characteristics and influencing factors of high ground stress and large deformation of altered granite tunnel are discussed and analyzed by means of rock test,monitoring measurement,numerical calculation analysis and geological comprehensive analysis.The altered granite tunnel project area is strongly affected by the structure,the alteration characteristics are significant,the rock mass structure is loose,and the altered granite stratum provides sufficient source conditions for large deformation.The tunnel site monitoring measurement shows that the altered granite section with large deformation is closely related to groundwater.The content of hydrophilic minerals such as illite-montmorillonite and chlorite in the altered granite is high,and it is easy to disintegrate in water,which greatly reduces the ability of rock mass to resist deformation.Based on the geological conditions and in-situ stress test of the tunnel,the initial in-situ stress field of the tunnel is analyzed by inversion.It is found that the altered granite tunnel is mainly horizontal tectonic stress,and the tunnel is mostly in a high in-situ stress state along the tunnel,which provides internal dynamic geological conditions for the occurrence of large deformation.According to the analysis of supporting deformation and monitoring measurement during tunnel excavation,the influence of complex geological conditions on tunnel design and the quality of construction technology and supporting structure are important human factors causing large deformation of surrounding rock.