Abstract:

The karst groundwater is one of the most important and active master control factors inducing geohazards such as water outburst and mud gushing, it is of great significance in the evaluation, prediction and control of geohazards. The mechanism of water-rock interaction in karst tunnel has been studied by using theories of karst geology, engineering hydraulics and fracture mechanics, and the effects of such mechanism on water outburst and projecting mud soil during the construction of karst tunnel has been explored; the mechanical mechanism of water gushing process has been analyzed. The research results show that sustaining action of karst water and water pressure on fractured rock mass and the excavation effect lead to water outburst and mud gushing by the way of hydraulic fracture; the mechanical functions of the sustaining action is embodied in four aspects: the softening and scouring mechanical effect of water-rock on fractured rock mass, the hydraulic fracture damage effect of water pressure on fractured rock mass of preventing water, the expanding mechanical behavior of water flow on passageway and the dynamic controlling effect of water pressure on flowing yield. Accordingly, based on fracture mechanics and plastoelasticity, the concept of minimum safety waterproof thickness has been put forward; and the expression of semi-analytical solution has been given; it has been proved by a case study. The reference basis can be provided to study on theory of prevention and cure for the water gushing in the karst area.

Key words: karst tunnel, outburst of karst water, mechanical mechanism, minimum rock mass thickness, semi-analytical solution