In Western China, mining area has the characteristics of thin bedrock and shallow-buried. The mine excavation and deep mineral production will change the stability of initial rock mass structure and the in-situ stress field. The rock fractures are fully developed and even result in a completely broken state of rock. To study the volume effect on the water-sand seepage characteristics in broken rocks, the seepage experiments were performed by a new seepage system of water-sand mixture, which was designed based on the CMT5305 electronic universal testing machine. The results showed that when the initial porosity of broken rock kept constant, the sand filterability of broken rock increased with the thickness of rock sample; the influence of the thickness of rock sample on the quantity of filtering sand increased with the initial porosity of broken rock; the filterability of broken rock increased to a constant value with the rock sample thickness; the influence of rock sample thickness on the water seepage was not obvious, and the initial porosity had a greater effect on the water-sandstone seepage characteristics than the rock sample thickness.


With the development of deep coal mining, more complicated mechanics problems appeared. The original structure and stress state of rock mass are changed by the process of mine excavation and deep mine mineral production [1]. It causes the rock mass fully fractured and even completely broken. The study on surrounding rock stability, disaster prevention and other scientific problems are more difficult [2]. The scholars of civil, oil, mining and other industries pay attention to the rock seepage characteristics and a series of studies on the seepage characteristics of fractured rock and fluid-solid coupling have been reported [3].

The water isolating properties of fragment rock mass depend on the seepage stability of water and sediment. Compared to the intact rock, fractured rock has the characteristics of higher porosity and permeability, and easily causes rock engineering disasters. In coal mining engineering, water inrush and flooding accidents usually occurred in water cut zones [3-5]. For example, during the water inrush disaster of Zhao Zhuang coal mine in June 2, 1984, the maximum water inrush amount is 2053m3/min [6]. The seepage characteristic of fractured rock is an important factor for the safety of coal mining. Scholars investigated the seepage characteristics from the aspects of particle diameter, porosity and stress distribution [7, 8]. Li Shuncai etc. [9, 10] performed the experimental research on the seepage characteristics of saturated fractured sandstone with time. Wang Luzhen etc. [11, 12] studied the effect of loading process on permeability of coal particle with size distribution.

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