Research On Theory And Technology Of Deformation Control By Stress Pre-relief In Soft Rock Tunnel With High Initial Geostress

The large deformation of surrounding rock often happens in the soft rock tunnel with highstress level construction, it seriously affected smooth construction. It can not achieve anideal effect by using traditional support pattern. Finding a valid deformation controltechnology becomes urgent affair. Stress pre-relief is a new support theory; the relatedtechnology has been applied on deep buried roadway by coal sector. But there is greatdifference between railway tunnel and roadway, can not apply mechanically. There is nosuitable stress pre-relief technology for railway tunnel. Moreover, the mechanisms of stresspre-relief remain unknown. It lead to the control theory is not mature and make thetechnology implementation with uncertainty.This article base on research status, and Lan Yu railway Mu Zhai Ling and Mao YuShan tunnels are backing project. Aiming at the above problems, the following studies arecarried on by the way of comprehensive use theoretical analysis, numerical simulation, fieldtest, and quantity statistics.(1)The deformation influence factors of soft rock tunnel with high stress level arestudied by combination of orthogonal test and finite element method, in order to analyze thefactors sensitivity of influence of surrounding rock. The reason of large deformation of MuZhai Ling tunnel No.7inclined shaft is investigated to make sure the primary and secondaryrelation of factors. According to the result, the article makes clear the necessity of usingstress pre-relief to control deformation.(2)The model of tunnel floor heave is built, and the result clarify the feasibility ofcontrolling the deformation by stress pre-relief, and reveal the stress pre-relief will enlargeplastic zone. Considering surrounding rock weaken caused by plastic zone enlarged, whenthe stress pre-relief technology implement, based on strain softening model, the relationshipbetween plastic zone and support pressure is derived. According to the inflection point of theresult curve, proposed the control principle for stress pre-relief.(3) Analyzing the influence of distribution of surrounding rock pressure and trend ofplastic zone for stress pre-relief by using the software FLAC3D, the result further clarify thetheory of stress pre-relief.(4) Combining the character of soft rock tunnel with high stress level, aiming at railwaytfunnel construction situation, proposed three kinds of stress pre-relief technology,including reserve-space way, pilot-heading way, drill hole way, based on principle which has been put forward, the key parameters of three kinds of stress pre-relief technology areoptimized, and put forward optimal plans.(5) The pilot-heading and reserve-space two kinds of stress pre-relief technology arecarried out in Lan Yu railway Mao Yu Shan tunnel. The tunnel deformation and the supportstress are analyzed. As the result, reasonable pre-relief technology can reduce thedeformation effectively and make sure the support system is stable.