Study On The Classification Of Grade Ⅳ Surrounding Rock And The Stability Of Surrounding Rock In Jinquan Tunnel

Stability of Surrounding Rock mass with the tunnels is a important research contents. To accurately understand it is the basis of rock engineering design、taking reasonable measures and ensuring safety.Howerver, it is extremely difficult to obtain the detailed geological parameters 、 surrounding rock parameters and parameters of designed load, because of the complexity of geological conditions 、 underground engineering and the limitation of method and means of prospecting. The rock mass classification during the design stage is frequently not in conformity with the level of rock mass at the construction site. Therefore, in the process of tunnel construction,the geological workers need to revise the surrounding rock classification and the parameters during the design stage, adjust the construction scheme.Associated with the project of Jinquan tunnel, the main Contents and results are as follows:① Through observation of field geological conditions, wo find there are obvious differences in lithology、strata thickness and the stability of the surrounding rock between import and export department of Jinquan tunnel.So, wo divide the rock classification into two sub grades: grade Ⅳ1 and grade Ⅳ2 by the methods of field observation、field TGP test and laboratory tests of rock physics,etc.② Adjust the original designed scheme of the construction methods and the initial support scheme, design the other two kinds of schemes after the classification of the surrounding rock.③ Using different programs to simulate the surrounding rock with different grades by Flac3 D. Research it’s stability by analyzing the stress state、displacement state and plastic zone state. Research results show that:1)Grade Ⅳ1 surrounding rock has some ability of self stability under the full face excavation 3M each time, in the original design scheme. The original design support scheme can effectively limit the surrounding rock deformation, when it can be applied in time.2)But grade Ⅳ2 surrounding rock has bad ability of self stability under the full face excavation 3M each time, the collapse ofen occurred before the initial support applied by the workers. The collapse phenomenon can be alleviated effectively and only a small range of rockfall occurred when the excavation footage is reduced to 2m. When the benching tunnelling method is adopted,the stability of the surrounding rock is enhanced.④ Monitoring measurement in tunnel site, analysis of displacement variation regular pattern. According to the monitoring results, wo can find that the overall stability of the tunnel surrounding rock is good, after the adjusted excavation method and supporting scheme is adopted.