Research On The Failure Mechanism Of Marble Area Groundwater Inrush In Jinping Second Class Deep Tunnels

Jinping second class deep tunnels were built in the Jinping large bent on YalongRiver, which was located in the joints of Muli, Yanyuan, Mianning of Liangshan YiAutonomous Prefecture, Sichuan.The tunnels were cross through the interfluve ofJinpingmountains, with the length of16.67km in average.The karst rock was widelydistributed,highly growth and with a lot of water in project area,which would causegreat threat to the safety of lives and propertiesby water inrush hazard.The theory model of groundwater inrush was built by the comprehensive analysison engineering geology, hydrogeology and property of groundwater inrush hazard ofJinping second class deep tunnels.Based on the theory model, a series of rockhigh-pressure failure experiment and high-pressure penetration experiment had beencompleted by the large rock high-pressure infiltration tester.And the mechanicalanalysis model of water inrush in marble has been concluded. With the combinativeanalysis of mechanical analysis model and numerical simulation, thefailuremechanism of marble area groundwater inrush in Jinping second class deep tunnelshad been discussed. Themainresultsareasfollows.1. Based on the analysis of rock water inrush failure model and water inrushexperiment, this paper made the conclusion that the three main controlling factors ofwater inrush failure were high crustal stress, high water pressure and the infiltration ofmarble. The higher the surrounding rock stress and infiltration pressure were, themore the rock proned to water inrushfailure. Not only would the increase ofinfiltrationpressure rise the water pressure in fracture and pores, but also reduce the rock peakintensity and promote the failure of rock.2. The experiment showed that: rock pressure, the higher the osmotic pressure, themore likely to occur inrush water.Increasing osmotic pressure will not only enhance the fissures and the pore water pressure, but it also reduces the peak intensity of therock, and promote rock destruction. at different stages.During rock get into the stablecrack growth stage high-pressure water on the rocks have a protective effect, guidedrock to resist the increasing stress by the deformation, that is only to extend the timefor rock failure, but it has little effect to improve the rock peak intensity.And as thepressure increases the major failure modes of rock gradually changed from the shearfailure crack damage to pressure failure. Once inside the crack propagation throughthe rock, high-pressure water to accelerate the destruction of rock, reducing the valueof the residual strength of rock. In some degree this explains the hysteresis quality andburstiness of the inrush.3. By establishing a new marble water inrush destroyed element fracture mechanicsanalysis model, combined with the stress conditions in the test sample unit cell, and tothe introduction of the high pressure water stress analysis. Three kind of criteria fordetermining crack rocks to prove that as the fissures filled with high-pressure waterthe state of stress fracture will be more stable.4. Using the finite element simulation method to analyze the stress conditions in theJinping second class deep tunnels area and the evolution of the stress in excavationworks get: Tunnel within the scope of baishan group regional stress condition ishigher than rock pond and miscellaneous valley group, the initial state of baishangroup of the first and the third largest principal stress65MPa and13MParespectively; In addition to the first principal stress of T3area decreasesed obviouslyin the process of excavation, the rest of the regional stress increased with the increaseof excavation depth.5. Combining the results of experiment, mechanical analysis model and numericalsimulation, the conclusion of the marble groundwater inrush mechanism were asfollows: the stress field and infiltration field of marble would redistribute under highfield stress and high water pressure after tunnels excavation, while the stress ofsurrounding rock intensively aggregated, and the water pressure ininfiltrationchannels increased. With the increase of the pressure, the rock entered the stage ofplastic deformation. With the effect of high-pressure water, rock produced a largeamount of minor crack to counteract the deformation, andextend the time of rockfailure, but at the same time lead the rock internal structure to fragmentation. At last,after the rock was completely broken, the pieces of fragmentized rock would rush outwith high-pressure water, which formd the water inrush.