Evaluation of the hydrogeological conditions
1. Introduction
The evaluation of the hydrogeological conditions generally includes diggings, mines, mining areas, working faces and coal seams. It studies the conditions of recharging and discharging groundwater, analyzes the factors of filling water, points out the main hidden water hazards, summarizes the main problems of preventing and controlling water, and is therefore the basis for guiding, developing and evaluating the technical measures and activities in relation to water control.
2. Main contents
The hidden dangers of water hazards faced by the subject of the evaluation are listed one by one, the degree and severity of the hazards are given, and the technical measures to control the hidden dangers of water hazards are proposed. The details are as follow:
(1) The production, location, traffic, topography, hydrometeorology and other basic conditions of the subject of the evaluation;
(2) Introduction to and comments on previous hydrogeological work;
(3) Brief description of the coalfield, tectonic geological unit and main strata where the mine is located;
(4) Introduction of the regional hydrogeological units, groundwater recharge, diameter and drainage conditions, etc., and analysis of the threat of various water sources for mining coal seams;
(5) Analysis of individual hidden dangers of water hazards, mainly including:
①Floor water hazard: focusing on the analysis and the study of the water-rich characteristics of the floor aquifer, the thickness, lithologic combination, physical and mechanical properties of floor water-resisting layer, the depth of mining damage of the floor and the water-resisting capacity of floor water-resisting layer among others, using water inrush coefficient and vulnerability index to evaluate the risk of water inrush.
②Roof water hazard: focusing on the exploration and the study of the development height and collapse angle of the "two belts", the hydrogeological characteristics of the aquifers affected by the "two belts", the tectonic development and water conductivity, whether there are poorly sealed boreholes, and the previous water prevention and control work and its effects; as for coal mining in shallow coal seam, weak cementation of roof layers, tectonic development area, under strong aquifer and under surface water body, the evaluation will be conducted in accordance with applicable specifications.
③Old goaf water hazard: focusing on the analysis of coal seams mined in small mines and old goaf, boundary of accumulated water, water level elevation, volume of accumulated water, spatial distribution range and its spatial relative position in relation to the area under evaluation, exploration and release effect of old goaf water, reliability of waterproof coal (rock) pillar, tectonic development and water conductivity, etc.
④The water inflow in the evaluation area is predicted and analyzed by appropriate methods, according to the mining connection planning, and the waterproof and drainage capacity of the mine and the evaluation area is evaluated according to the Rules for Coal Mine Water Prevention and Control.
⑤On the basis of the evaluation of hydrogeological conditions, prediction of water inflow and evaluation of waterproof and drainage capacity as described above, the main problems of water prevention and control in the evaluation area are summarized.
(6) Based on the evaluation of hydrogeological conditions, the technical approach of water prevention and control is proposed, the activities and the measures of water prevention and control work in the evaluation area are determined, and the opinions and recommendation for the next stage of water prevention and control work are given.
3. Typical Projects
CCTEG Xi’an Research Institute Co., Ltd. has carried out more than 400 hydrogeological condition evaluation projects, including the hydrogeological condition evaluation of working face I020201 of Hongliu Coal Mine of Ningxia Coal Industry Group referenced below as an example:
(1) The main water hazards in working face
The roof aquifer of working face I020201was rich in water, and the threat of water hazard was serious. F7, F7-1 and F8 water-conducting normal faults are developed, and the lithology combination of roof is complex, so there was the hazard of stratifugic water.
(2) Water control works and its effect
① Prevention and control of roof water in the working face and its effect evaluation
Drilling fields were arranged in the air way, belt transporter tunnel and cutting holes of working face I020201, and a group of fan-shaped underground upward-lifting holes were arranged, with a total of 155 holes, as shown in Figure 1.
After about 90 days' drainage, the water yield of the holes reached a dynamic and stable state, and the hydrostatic reserves of roof sandstone were effectively drained, reducing the threat of roof sandstone water to mining face to the greatest extent.
Figure 1 Design of water prevention and control in working face I020201
② Prevention and control of fault water and its effect evaluation
Twelve drainage boreholes were designed for three faults, changing fault water from pressure-bearing to non-pressure state and maintaining the water inflow in a stable trend, so as to realize safe mining in the working face.
(3) Design of stratifugic water prevention and control
Preliminarily, 18 boreholes in 3 drill yards were designed. If the stratifugic water was identified in the boreholes, dense drainage boreholes could be optimized. The design plan is shown in Figure 2.
Figure 3 Layout of the boreholes for stratifugic water exploration and discharge
(4) Main conclusions
Through the analysis of geological and hydrogeological conditions of working face I020201 in Hongliu Coal Mine, combined with the specific conditions of the working face, the water-filling factors and the predicted water inflow of the working face were analyzed, and the effect of the water prevention and control works carried out in the early stage was evaluated. The first 300 m section near the cut of the working face has already had the hydrogeological conditions for mining.
FAQ
Q1: What factors should be emphatically analyzed for floor water hazard?
A: Water richness of water-filled aquifer, thickness of bottom water-resisting layer, lithology combination, physical and mechanical properties, bottom damage depth and water resistance of bottom water-resisting layer.
Q2: What factors should be analyzed for the old goaf water hazard?
A: Coal seams mined in small mines and old goaf, boundary of accumulated water, water level and accumulated water volume, spatial distribution range and their relative spatial position in relation to the evaluation area.
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