Calculation of water-retention thickness for broad applicability and mining influence in Mu Us Desert area

Multiple near-surface aquifers in Mu Us desert are regarded as critical supports of region ecological environ-ment,production and life. It is urgent to study on water-preserved coal mining. However,as the core content of water-preserved coal mining research,due to the various characteristics and the vertical position of the aquifers,some “water-retention thickness” calculation methods have limited application scope and lack unity. Characteristics and hydrogeo-logical properties of aquifer and aquiclude at horizontal and vertical distribution in Mu Us Desert are analyzed. Combined with the engineering geological conditions of different area and mining methods,the definition of water-retention thickness is discussed. The whole layer above the coal is divided into three parts:target protection aquifer,predicted water diversion section and equivalent water-retention section (consist of active bedrock and clay aquiclude,main wa-ter-retention section). Water equilibrium principle is adopted to analyze the water-retention characteristics of bedrock and clay aquiclude. “ Water retention proportional coefficient” is applied to determine the water-retention thickness calculation method in bedrock and clay aquiclude. Combined with the computing of predicted water diversion section, the model to calculate the water-retention thickness is established which can be applied to the regions of “ sand-clay-Luohe aquifer-bedrock”,“sand-clay-bedrock”,“sand-bedrock” and “burnt rock”. According to the positional relation between the water diversion and bedrock,clay aquiclude,scale relation between the altitude from the target protection aquifer to coal and water-retention thickness,the zoning standards for natural water-retention areas,general water loss areas and severe water loss areas are formulated. Besides,the established model is put into use in Xiao Baodang coal mine of Yulin-shenmu coalfield to calculate the water-retention thickness,where the “sand-clay-bedrock” and “sand-bedrock” regions distribute. In addition,the coal mining influence to the unconfined aquifer is evaluated. The calcula-tion model of water-retention thickness and the zoning evaluation standards of mining have a good adaptability. A new idea for the calculation of water-retention thickness and the evaluation about the influence of coal mining on the overly-ing aquifer is also presented.