Abstract: To investigate the mechanism of water and mud inrush in water-rich fault fracture zone, a large-scale indoor water and mud inrush test system considering mass transfer and crustal stress state is developed. The simulation test of water and mud inrush disaster evolution process in fault fracture zone under different hydraulic loading modes and medium parameters of fracture zone are carried out by using the device. Some findings are as follows. 1) Evolution of water and mud inrush disaster in fault fractured zones is a strong coupling process of seepage and erosion. Fine particles in the filling of fracture zones first migrate under the water pressure. With the continuous migration and loss of fine particles, the flow pattern changes from laminar flow to turbulent flow, which eventually leads to water and mud inrush disaster. 2) The larger initial porosity of filling in fractured zone and the higher of applied water pressure will induce the water inrush more easily. As a result, the evolution characteristics of seepage exhibit more obvious in the test, the increase of seepage field parameters such as permeability, porosity and Reynolds number are much faster, and the seepage field parameter evolution curves suddenly increase. 3) The evolution characteristics of water and mud inrush are more obvious under gradient loading than under constant water pressure loading condition, and the critical water pressure of water and mud inrush from filling is smaller. A generalized model of permeability evolution characteristics of fault is established with analysis of fluid state conversion on the relationship between water inflow rate and time (Q-t), the relationship between hydraulic gradient and water inflow rate (i-Q), and the evolution characteristics of permeability on the relationship between permeability and hydraulic gradient (k-i). The results provide guidance for evolution mechanism and prevention measures of water and mud inrush disaster in fault fractured zone.

Key words: fault fracture zone, experimental study, water and mud inrush, characteristics of seepage evolution