Research About Cavitylining In Water’s Effect On Stability Of Tunnel

To use the New Austrian tunnelling method to build tunnels，especially whichinvolves groundwater, accidents such as water gushing-out may easily happen if thestress control of groundwater is inappropriate. These accidents will endanger the livesof constructors and increase construction costs，and also can influence the safety andmaintenance of the tunnel while using of tunnel.In recent years, our country has accomplished a lot of mountain tunnels，underwater tunnels，and mine tunnels. Cases that tunnels come through cavity haveincreased following those accomplishments. Due to the possible-existing high waterpressure in the cavity，it is easy to induce water inrush which will significantly affect thesafety of on-going tunnel construction. According to this situation，this essay hasthoroughly studied the secure thickness between the cavity filled with water pressureand tunnel face through analyzing worldwide existing achievements and calculatingthe numerical simulation. The main contents and achievements have been attached asfollows.①Firstly, the essay summarizes the causes of the water inrush of a tunnel. It showsthat water inrush is mainly aroused by water pressure, rock structure, physicalmechanics, the area’s engineering geological conditions, the size of a tunnel section,digging speed, and reserved secure thickness as well.②Secondly, by analyzing and simulating the existing project’s data and also on thecondition of a steady water pressure, it studies the thickness between the cavity and thetunnel face when the water inrush happens in a tunnel with the fluid structureinteraction. Accordingly, it concludes that reserved secure thickness between a cavityand the tunel face shouldn’t be less than6m under a2MPa water pressure.③Thirdly, it studies how the secure thickness between cavity and tunel facechanges in several different water pressures, and the influence rules of the surroundingrock level on secure thickness。The study results show that each time the water pressureincreases0.5MPa, the secure thickness between cavity and tunel face also increases2mto4m; besides, the proportion of an accident will be extremely high if the surroundingrock level decreases.④Fourthly, it studies the secure thickness between tunnels and cavity in differentcavity distribution by analyzing the existing project data. It shows that on the hypothetical condition of the third the surrounding rock level, the secure thicknessshould respectively be8m,12m and16m with different cavity water pressure like1MPa,1.5MPa and2MPa when the cavity position is at the top of the tunnel; the securethickness should respectively be changed to8m，12m and16m with different cavitywater pressure like1MPa,2MPa and3MPa when the cavity position changes to theright side of the tunnel.