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