Study And Evaluate Of Stability And Water Gushing Of Surrounding Rockmass In Karst Area Tunnel In Leguang Freeway

With the depth of the western development and the gradual perfection of the national freeway net, a growing number of tunnels are built in Karst areas. The biggest problem of tunnel construction in karst areas is the stability of surrounding rock and the sudden inrush geological disasters. So researching on the stability of tunnels in karst areas and the application in engineering has very important engineering significance in theory and practice.Combining to special research projects in Karst Tunnels in segment of Pingshi to Zhangshi in Le-Guang freeway and special research projects in Chang jiling tunnel, this paper takes Chang jiling tunnel as research object, based on field survey conmbining reduction in studio, experiment verify conmbining theoretical analysis, and the comprehensive use of more methods, and studies the stability of rockmass and gushing evaluation. The main tasks are as follows:1. Study the background of area geological, the hydrogeology and engineering geology conditions. Summarizes the development laws of Karst area, and investigate the geological conditions which can cause bad influence to stability and water gushing of the tunnel.2. Study of effect factors of tunnel stability and classification of rockmass.Evaluate the effect factors to the stability of tunnel, and study the grade of rockmass and stability by classification of surrounding rockmass, which can provide a basis for further study.3. Study of numerical simulation to tunnel stability. With the help of ANSYS and FLAC3D software, analysize the displacement, stress and plastic zone of rockmass, which is in case of supporting,and study the undermine mechanism and stability of surrounding rockmass in ZK91+600～ZK91+650 of the tunnel.4. Study of water gushing especially in Chilaoding area.According to Karst tracing experiment, this paper investigates the flowing direction of underground water and the effect to the tunnel. Estimate the gushing of every karst cave or sinkhole and the total by using experience formula, and calculate the total average and the largest gushing of every day in the subarea which can bring great effect to the tunnel with the help of dividing areas. 5. Discuss the prevention measures to karst tunnel.Poinging to the main contents above, the conclusions are as follows:1. The area of Chang jiling tunnel contains 42 karst caves (9 in the left,3 in the middle and 30 in the righe) and 20 structural belts which including 9 fault broken belts,3 unconformable contact lines and 8 fault clearances. All these structural belts provide a good channel for the transport and store place of underground water, and also bring bad effect to the stability of tunnel, water gushing and ground settlement.2. Evaluate the main factors such as strata and thickness, attitude of rock, geological structure, morphology and spatial distribution of cave, filling conditions and the hydrogeology conditions to the tunnel, and draw a conclusion that all factors are associated and can transformed in a certain condition.Caves on the lefe, Karst caves,geological structures and hydrogeology conditions affect tunnel mostly.According to rockmass classification, most rockmass grade of the tunnel areⅢandⅣwhich reach 77%. Most of the surrounding rockmass is between stability and instability, and can earlily cause destroyed or water gushing in case of unsupport for broken rockmass, fault broken bells and underground water.3. Taking ZK91+600-ZK91+650 of tunnel as the subjece,with the help of numerical simulation, the largest displacement in X direction reach 22.31mm,29.25mm in Y direction in case of support, The undermine mechanism of tunnel is tensile broken and the displacement tends to a convergence trend inside of both tunnel and karst cave. The most dangerous places are between tunnel and karst cave, and the places which can cause stress concentration mostly are between tunnel and karst cave, especially in arch waist.4. According to ion tracer test, water from ZK90+120m-ZK91+930m flows from ZK91+930m to ZK90+120m which is at the entrance of the tunnel alonging the tunnel axis, water from ZK91+930m-ZK92+152m flows from ZK91+930m to SW direction which is vertical of the tunnel axis, water from ZK93+147.6m～ZK94+40m flows from ZK93+147.6m to ZK94+40m which is at the exit of the tunnel alonging the tunnel axis. The underground water of the karst cave which is on the left side of the tunnel can cause water gushing to the tunnel while the right side is not. According to estimate the water gushing of every karst cave, the details of every karst cave can be seen at table 4-2 and the total water gushing reachs to 7446.9m3/d. There are 12 hydrogeology geology subareas, and the total average gushing of every day reaches to 15135m3/d, while the largest gushing reaching to 1505695m3/d. There is also a big underground water area in the ZK91+700m of Chilaoding, and the flow rate of water reaches to 191.2m3/s when the water level is normal, while reach 390.6m3/s in case of extreme situation.5. Sum up the prevention measures to karst water, karst cave and fillings, which provides theoretical basis for further prevention measures.