Quantitative Evaluation Of Mining-induced Disturbance On Groundwater System In Coal Mines

As a key component of natural hydrological cycle, groundwater system is the inevitable basic element for life supporting system on the Earth. So, how to exactly understanding and evaluating mining-induced disturbance on groundwater system in coal mines are of great significance for protecting groundwater system and regional sustainable development.The main object of the dissertation is the groundwater system in coal mining areas. On the basis of theoretical analysis and numerical calculation of groundwater system disturbance caused by coal mining, the dissertation focuses on the quantitative evaluation of groundwater system disturbance in coal mining areas, and puts forward an evaluation system, in which water inrush coefficient is seen as the critical factor.From the viewpoint of system theory, this dissertation firstly introduces the definition of groundwater system in coal mining areas, as well as its composition and features of self-organization based on a systematical literature surveying. Then the different kinds of the function of groundwater system in the interaction among water resource, environment and human being, as well as natural water cycle, including mine water hazards, are discussed in detail. In a coal mining area, the groundwater plays not only the role of the component of water cycle, but also as an important water source both for the normal production and for water disaster.From the theory of human-earth system, the paper also introduces the interaction between human activities and earth system in mining areas, summarizes the mining- induced disturbance on different subsystems, like aquifer and aquitard subsystem, water chemical subsystem and water resource subsystem. The coal mining area is a typical human-earth system in a smaller dimension, where the interaction between human and earth is very fierce. The breaking of roof or floor of coal seam could lower the storage and migration capability of groundwater system and cause disturbance on the aquifer and aquitard subsystem. Mining activity not only changes the occurrence of coal seam, but also disturbs the water chemical subsystem, resulting in acidized, mineralized water, suspended substance in mine water. Because of the drainage of mine water for safety production, the amount of water resource in mining areas decreases obviously.In the dissertation, the mining-induced disturbance on groundwater system is evaluated by means of the factors, such as groundwater depression cone and water inrush coefficient. This paper proposes the conception of water inrush coefficient and the evaluate indicator system integrating with the actual situation of coal field. The drawdown and radius of groundwater depression cone can be calculated by data of observational material of water level in observation drills, so the disturbance on groundwater system can be quantitative evaluated. Water inrush and rainfall are the important technical information in mine. Water inrush coefficient (y) is conformed by annual water inrush (Wa), annual rainfall (Ra) and area of mine(Am) as y = Wa /( Ra·Am). Five classes of disturbances can be recognized by comparing water inrush coefficient(y) with coefficient of recharge from precipitation (b). Time series of water inrush and rainfall could be calculated for modeling and predicting using ARIMA. So the water inrush coefficient that is consisted by water inrush and rainfall could not only be used for quantitative evaluation, but also for prediction of the disturbance on groundwater system.As a case study, the water inrush coefficient was calculated based on the data from study area Hanqiao Coal Mine in Xuzhou, China. The results indicate that the evaluation system is feasible. Taking the water inrush of 1973-2008 as an example, the use of ARIMA model was introduced and the prediction to rainfall was verified in the dissertation. The water inrush coefficient is between 0.885 and 2.553. The degree of disturbance isⅤ, the highest. The reason is that water drainage results in lowering of the groundwater table in mining and the groundwater system had been disturbed violently.Innovations in the dissertation include:①The dissertation takes the groundwater system in coal mining area as the focus of the study, instead of mine disastrous inundation prevention. It explores an indicator system for quantitative evaluation of mining-induced disturbance on groundwater system.②For the first time, the concept of water inrush coefficient is proposed in this dissertation and used in the evaluate indicator system mentioned above.