Mining-induced Floor Failure And The Model, Precursor And Prevention Of Confined Water Inrush With High Pressure In Deep Mining

In the water disaster prevention practice of deep mining above aquifer, there is always a basic contradiction between the floor aquifuge with different structures and the water pressure that the aquifuge is subjected to. Therefore, the further study and understanding on the floor structure and mining-induced failure characteristics, the high pressure water inrush models and precursors are significant for efficiently prevention of the water inruch hazards.This paper presents the models, precursors and characteristics of complex structure aquifuge failure in the floor and the confined water inrush with high pressure over 5MPa in deep underground coal mining. The occurrence and influencing factors of floor water inruch, interaction between water and rock, temporal-spatial distribution were analyzed based on numerous water inruch data. And then, two basic patterns of floor water inruch, including integrated and fractured floor water inrush pattern, were concluded and summarized. The characteristics of floor failure under deep mining conditions were revealed according to field measurements, numerical and physical simulations. The results show that, with the condition of confined water pressure over 5MPa that the aquifuge is subjected to, the floor failure is influenced significantly by advance stress and the failure depth is about 25m. The failure depth and range are enlarged with the increasing of water pressure under the same floor structure and mining conditions. There are some differences of the failure range exist from the area under the working face to the goaf, the ranges change gradually from"inverted saddle shape"to"inverted ladder shape". Three scaled models, including simplex structure, multilayer structure and faultage structure for floor water inruch with high pressure were then designed and established with the high pressure water inruch simulation equipment. And then, the basic characteristics and laws of stress and pore water pressure variation during the water inruch process with high pressure induced by coal mining under different floor aquifuge structures were also systematically summarized on the basis of the experimental results. The periodic fluctuation of the floor stress and pore water pressure due to coal mining are closely related to the mining progress. During the conformation of mining-induced water inrush pathway, all the parameters increase sharply and fluctuate violently. When the water inrush into the working face, all the parameters decrease considerably and then at a certain range of a low level for a long period. It can be deduced from these results that the floor stress and pore water pressure can be significant precursors for monitoring and forecasting the water inrush hazards in coalmines. Safety mining practices under typical floor acquifuge conditions were then summarized. Evaluation method of safety deep mining under high pressure and thick acquifuge condition was established. Then, the example of"floor water abundance exploration-grouting for aquifer alteration-physical and drilling exploration verification- safety mining evaluation-coal mining"under high pressure and thin aquifuge condition was put into practice. It was found that at least 20～30m of the upper Cambrian limestone can be considered as aquifuge because of its poor karst development characteristics and impermeability And then, the viewpoint has been successfully applied to the decision making of excavating the shaft bottom at -350 m level and 55.5 m deep into the upper Cambrian limestone at a coalmine of central Henan Province and a total 320 m long tunnel in the shaft bottom has been excavated safely and put into practice for 2 years.The achievements of this paper lay an important basis for monitoring and forecasting the water inrush disasters in deep undeground coalmines, and for safety coal mining above aquifer with high pressure.