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Abstract Maluqing tunnel of Yichang—Wanzhou railway goes through a water-enriched high hydraulic pressure latent karst cavity in DK255+978 m，where the water pressure reaches up highly to 160 m and maximum volume of water to 1×106 m3，soil-break and water-inflow disaster had taken place for 19 times. Based on characteristic of large scale of cavity water，high hydraulic pressure，high bedload content，strong destroied power，no foreboding，paroxysmal and intermittence，antinomy between paroxysm and arrearage，etc.，adaptability of treatment measure is defined based on mechanics，such as，seepage enlarged into conflux because of pressure dispersion between inside and outside of the cavity，so that cavity deprives groundwater from aquifer aqueduct and fracture，then，the water together with mud release suddenly. It is found that the principle of energy releasing and pressure reducing (ERPR) should be adopted to evade risk during construction temporary stage and permanent working stage，while the energy stored in the cavity must be released，and water and soil pressure on tunnel and its structure must be reduced，so that plastic district acting on cavity wall due to high pressure doesn¢t develop and connect with the plastic district act on rockmass due to tunnel excavation or water and mud drainage. Boundary of karst cavity，filling component and distribution characteristic must be explored distinctly by synthetical geological forecasting. Pressure and quantity，especially，critical distance determine thickness of pressure bearing rock wall. The feasibility of space-cross-step scheme of drainage aloft and purge filling infra is analyzed and validated.
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Received: 09 June 2009
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