岩溶隧道掌子面突水机制及岩墙安全厚度研究

从断裂力学角度分析高压岩溶水作用下裂隙扩展机理,认为自然营造力作用下水力劈裂多属压剪破坏模式。运用断裂力学和水力学理论分析隧道掌子面突水滞后效应和扩径效应,指出:裂纹扩展跳跃性在宏观上表现为隧道掌子面突水的滞后性;掌子面突水通道最终形成需经过多个阶段,其最终尺寸受岩溶水压力、掌子面岩体质量等因素控制。认为隧道掌子面突水是由于开挖扰动降低了水压劈裂的临界水压力造成的。据此观点,建立基于临界水压力的掌子面岩墙安全厚度计算公式。以宜万线云雾山隧道为例,计算得到岩墙最小安全厚度与施工中普遍采用预留厚度较为一致,说明此方法较为合理,可为类似工程提供参考。

Study on Water-Inrush Mechanism and Safe Thickness of Rock Wall of Karst Tunnel Face

The frequent occurrence of the water and mud inrush caused by the karst cave with high pressurized water ahead of tunnel faces remains a critical problem to be researched and resolved in tunnel construction in karst areas.The mechanism of crack extension under high karst water pressure was analyzed from the view of the fracture mechanics.Hydraulic fracturing under natural pressure was mostly considered to belong to the compression-shear(type Ⅱ) failure mode.The hysteresis effect and diameter-expanding effect of the water-inrush of tunnel face were studied by applying the fracture mechanics and hydromechanics.The results show as follows: The hysteresis effect of the water-inrush is the macro-view property of the skip of crack extension;the final formation of the water-inrush passage needs undergoing multiple stages;the final size of the water-inrush passage is controlled by factors such as the karst water pressure and the quality of the rock mass of tunnel face and so on and so forth;the water-inrush occurs in the vicinity of the tunnel face due to decreasing of the critical water pressure of hydraulic fracturing which is caused by excavation and disturbance.Accordingly,the calculating formula of the safe thickness of rock wall was established on the basis of the critical water pressure.Taking the Yunwushan Tunnel of the Yiwan Railway Line for example,the minimum safe thickness of rock wall was calculated and the calculated value was found in good coincidence with the present value in construction.Therefore,the proposed methods are proved feasible,they can provide reference for similar engineering projects.