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Abstract With the introduction of the equivalent hydraulic conductivity of pipe flow for the water inrush of confined karst cave，a nonlinear model of coupled seepage-pipe flows was established to simulate the entire process of water inrush. The model was combined with the strength reduction method and solid mechanics to study the change of flow state of water inrush of confined karst cave. The instability of water blocking rock pillar and the water inrush occurred at Qiyi mine in south China were discussed. The water discharge from the working front increased with the increasing of the reduction factor of the strength of the water block rock pillar before the rock pillar losing its stability. After the failure of the rock pillar，water burst out from the confined karst cave to form pipe flow. The amount of the water irrupted reached the peak value in a short time then decreased slowly according to the simulation. The turbulent flow at the initial stage was changed into the laminar pipe flow finally due to the limited water reserve of the karst cave. The safety factor of water blocking rock pillar was introduced and the relations of the safety factor，the water pressure in the karst cave and the thickness of the water blocking rock pillar were studied. The thickness of the water blocking rock pillar with the safety factor of 1.5 was proposed to be the calculated safety thickness. The safety thickness of the water blocking rock pillar was proposed to be equal to the sum of the depth of blasting hole，the depth of blasting disturbance and the calculated safety thickness.
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Received: 28 April 2014
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2014, Vol. 33 
