Experimental Study On Migration And Evolution Of Qucksand In Western China Coal-rich Region

As coal-rich strata in western China, the Jurassic–Cretaceous has differences from the Carboniferous-Permian in north china type coal field in diagenetic time, geological processes, and so on. Thus those differences cause different types of coal mine disasters in the east and west. The paper got the support of National 973 Project “fundamental research of geological disaster prevention and environmental protection caused by high intensity mining in western China”(project num. 2013CB227901). Based on geological genetic background, combining with the typical case of quicksand, a conceptual hydrogeological model was established and laboratory test system for critical water level of quicksand was researched and developed independently. Laboratory test as main research means, the characteristics of quick migration and the starting mechanism of quicksand were discussed.The main contents and results of this paper are as follows:(1).Based on geological genetic background, combining with the typical case of quicksand, a conceptual hydrogeological model was established.Combined with analysis of particle size distribution, three basic sand samples, coarse sand, medium sand, fine sand, and two field sand samples were prepared, and orthogonal test, a total of 13 group, was carried out for discussing the evolution of dry sand and saturated sand, critical water level of subsaturated quicksand.(2).During laboratory test, critical water level of quicksand, evolution process, pore water pressure were observed and recorded. According to the observations, based on different water content, sand could be divided into three layers: saturated sand zone, subsaturated sand zone, dry sand zone. At early stage of quicksand, a cavity generated in saturated sand zone. With expansion of cavity, sand funnel appeared and subsaturated sand and dry sand moved down in turn till the funnel and the cavity is connected.(3). According to the different of appeared sand funnel, the subsaturated sand funnel evolution process can be divided into four stages: cavity forms stage, sand funnel rapid expansion stage, sand funnel stable expansion stage, connection with funnel and cavity stage. The dry sand funnel evolution process can be divided into three stages: sand funnel rapid expansion stage, sand funnel stable expansion stage, sand funnel instability stage.The saturated sand funnel evolution process can be divided into three stages: cavity forms stage, center collapse stage, edge collapse stage.(4). When dry sand occur quicksand, the sand with smaller particle size move faster. When subsaturated sand occur quicksand, the sand with bigger particle size and greater moisture content move faster. And with subsaturated sand layer thickness increasing, more water and less sand break out.Regression analysis of sand mass over time under critical water level of quicksand show that sand inrush mass and inrush time have a good exponential relationship.