Study On Mechanism Of Seepage And Water-inrush From Filled Karst Conduit In Tunnel

With the development of China's western development and “Belt and Road Initiative” strategy,a large number of major infrastructure projects are being built in the western karst area.In the western karst area,the karst conduitgeological structure possess extensive supply network of water.Water inrush of karst conduit always causes serious engineering disasters and environment damage.Study on characteristics and mechanism of filled karst conduit water inrush has important guiding significance for engineering construction and disaster prevention.In this paper,filled karst conduitwastaken as research object,basing on physical model test and theoretical analysis.This paper studied the seepage evolution law and structural instability characteristics of filling material with different permeability coefficient under different water pressure.Meanwhile,the critical condition of the instability of filling and the criterion of water inrush were also analyzed.(1)In the engineering background of Qiyueshan tunnel,fluid-solid coupling similar material were prepared basing on the physical and mechanical properties of conduit wall specimens and filling materials.The physical model test design was simplified by the geological condition of the site.Large scale physical model tests were carried out for different types of conduit filling.(2)For different types of conduit filling,the conversion of flow state and structural instability process are different.And they are separated into three types of instability: sand gushing instability,water gushing instability and mud gushing instability.By monitoring the variation of pore water pressure in the filling,this paper studied the evolution rule of the internal seepage,the average hydraulic gradient and the adjacent hydraulic gradient.(3)According to the different types of instability of conduit filling,the sliding mechanics model(mud gushing instability)and local instability mechanics model(sand gushing instability and water gushing instability)were proposed.The limit equilibrium conditions of the instability of conduit filling were obtained for sliding mechanics model and local instability mechanics model.A new hydraulic gradient was defined as the criterion of water inrush,and the critical values of two kinds of hazard criteria were analyzed.