Abstract
The mechanism of water flow in and around the bulkheads and the surrounding rock is studied for Panel No. 21102 in the Sanhejian coal mine in Xuzhou, China. Based on an analysis of the properties of the bulkheads and the surrounding rock, three types of water conducting pathways are identified: (1) a water conducting pathway at the interface between the bulkhead and the surrounding rock; (2) a water conducting pathway in the faults of the rock; and (3) a water conducting pathway in the fractures of the rock. The possibility of these three pathways for water flow at Panel No. 21102 is analyzed, and the connectivity coefficient of the water conducting pathway is determined. The expression for calculating the critical hydraulic gradient of the rock by using the connectivity coefficient in the water conducting pathways is presented which is based on the permeability and integrity of the rock. The ratios of the critical hydraulic gradient to the steady state hydraulic gradient are calculated for 13 mines in China. An acceptable safety factor in controlling the water flow for the bulkhead is found to be 1.68. When the safety factor is less than 1.68, water leakage has occurred in a number of cases. Finally, changes in the water pressure in the bulkheads with time and changes in the seepage flow with time in the surrounding rock are analyzed. It is found that there is a good correlation between the rate of water flow and water pressure which confirms that water pressure plays a decisive role in controlling seepage from the rock in and around the bulkheads.
Highlights
One of the main coal mining incidents in China deals with the problems of sudden inrush of water into the mine which often results in significant economic losses in coal production and seriously threatens the safety of underground miners [1, 2]
As underground coal mining in China gradually goes deeper with complex geological conditions and high ground stress, the activities result in more frequent accidents [3]. e hydrogeological conditions of underground mines become more complex with increase in the depth of the mines [4, 5]
Together with more damage and disturbances caused by coal mining to the original strata [6], the risk of water inrush in coal mines is greatly increased. erefore, effective prevention and prediction of water inrush in mines are very important tasks [7, 8]. e construction of water bulkheads is a common measure to prevent and control water inrush in coal mines. e purpose of a water bulkhead is to effectively isolate the flooded part of the mine due to water inrush from the normal production part to provide a safe working environment for the miners [9]
Summary
One of the main coal mining incidents in China deals with the problems of sudden inrush of water into the mine which often results in significant economic losses in coal production and seriously threatens the safety of underground miners [1, 2]. Harteis and Dolinar pointed out that some of the important factors that should be taken into consideration in the designing of bulkheads are the behavior of the contact surface between the bulkhead and the surrounding rock, and the water pressure that acts on the bulkhead [17] Some countries, such as the United States and Canada, have done comprehensive studies on the design and construction of underground bulkheads in coal mines with appropriate supervision and construction standards [18, 19]. Erefore, in comparison to international standards, improvement is needed in the design, construction, regulations, and operations of water bulkheads in underground mines in China An improved three-dimensional displacement measuring system was developed to measure the displacement fields [24]. erefore, in comparison to international standards, improvement is needed in the design, construction, regulations, and operations of water bulkheads in underground mines in China
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