Study On Classification Method And Key Technologies Of Deep Tunnel In The Fully And Strongly Weathered Granite Formation

Granite is a common stratum lithology in tunnel construction.Weathered granite is a weathered rock mass produced by certain physical or chemical action of granite.Under the action of weathering,the integrity of granite is destroyed and the physical and mechanical properties of rock mass have changed to some extent.Since the end of last century,many experts and scholars at home and abroad have carried out a study on weathered granite.Series of research,especially for highly weathered fully weathered granite,has launched a lot of research.In China,weathered granite strata are widely distributed in Yunnan,Hunan,Jiangxi,Guangxi,Guizhou,Guangdong,Fujian and Hainan provinces to the south of the Yangtze River.Most of these areas are located in subtropical areas.They have similar climate,humid climate and abundant rainfall.Therefore,granite is very vulnerable to weathering.The development of joints and fissures in weathered granite,especially the fully weathered granite,makes the weathering process go deep into the rock mass,which seriously damages the internal structure,structure and integrity of the granite rock mass,and greatly reduces the shear strength,compressive strength and overall stability of the rock mass.Generally speaking,the strength and stability of weathered granite in natural state have a great correlation with water content.After immersion,the strength of weathered granite decreases obviously.When tunneling in this stratum,it is easy to encounter such engineering problems as face collapse,water inrush and mud inrush.Based on the above reasons,it is of great engineering significance to study the classification of fully weathered granite and the shutdown technology of tunnel construction in fully weathered granite stratum.In this paper,combined with the Mengma tunnel project of Dalin Railway,the following research work is carried out:(1)Based on the physical and mechanical test of surrounding rock and statistical analysis of investigation,the basic physical and mechanical properties of fully weathered granite are explored,the relationship between shear strength index and water content is revealed,the range of physical and mechanical parameters of fully weathered granite is given,(2)The classification index system of fully weathered granite surrounding rock is established,and the classification method of fully weathered granite surrounding rock is put forward.(2)Based on field monitoring data and multivariate regression analysis method,a load correction calculation method for tunnel in fully weathered granite stratum is proposed,and the load correction calculation formula is given.(3)The different construction methods of tunnels in fully weathered granite strata and the failure modes of tunnel face under different surrounding rock classes are explored.The reasonable excavation methods of tunnels under different surrounding rock classes are put forward.The influence of water cement ratio on grouting performance and grouting effect of tunnels is revealed,and the reasonable grouting ratio of tunnels is put forward.