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The waste pits and roadways have been drained for a long time, and they are filled with water. This kind of water is called the old mine water, which is also called old water and old kiln water. When the production tunnel approaches it, the water becomes a source of water inrush. The characteristics of such water source water inrush are that the short-term water inflow is large, the force is fierce, and it is very destructive and easily causes a flooding accident. At the same time, the water is acidic and corrosive, often accompanied by toxic and harmful gases, which is very harmful to safe production.
Viewing Hydrogeology of Deposits from Mine Safety
Mine geological work is an indispensable basic technical work in mining. It refers to the geological work directly for production in the production area or mining area of ​​the deposit in the mining process, according to the needs of the mine work. The geological work of the mine geological work Based on the project of mine mining activities, it is the technical basis and basis for mining production and management activities. The mining activities must be moved with the advancement of mining operations. There is no fixed working space and place, and the working environment conditions are greatly affected by engineering geology and hydrogeological conditions. Therefore, in order to ensure the smooth progress of mining activities, it is necessary to understand the impact of mine geological structure, hydrogeology and rock properties on mine safety.
Water in nature exists in the atmosphere, the surface of the earth's crust, and the earth's crust. The water in the atmosphere is called atmospheric water. The water on the surface of the earth's crust is called surface water. The water in the earth's crust is called groundwater. The science of studying the origin, distribution, burial and movement of groundwater, the physical, chemical properties, and the relationship with rocks is called hydrogeology. The science of specializing in the groundwater of deposits and the treatment of groundwater during the development of deposits is called deposit hydrogeology. The purpose of studying the hydrogeology of the deposit is to make full and reasonable use of groundwater resources, and to effectively prevent the impact of groundwater on mine production and construction, and to ensure the safety of mining mineral resources.
1. Mine water and its harm to mine production
During the construction and production of mines, groundwater, surface water and atmospheric precipitation flow into the open pits and underground roadways through dripping, dripping, gushing water and sudden water intrusion. This kind of water is called mine water. In addition to increasing construction investment and production costs, pit water also causes damage to mine safety production, mainly:
(1) During the construction period, when the amount of water inflow is too large, it is necessary to take measures to increase investment, hinder the construction progress, and affect the quality of well construction;
And the open pit mine roadway water corrosion of various metal devices (2) having aggressive (such as a rail, and a variety of mining machinery bracket), pollution of the work environment;
(3) The pit water reduces the stability of the roof, floor and side slabs of the tunnel, and increases the difficulty of support and maintenance;
(4) In open pit mines, groundwater often destroys the stability of the slope, causing slope collapse and landslide accidents, affecting normal production, and even being forced to stop production;
(5) The local quality is unclear. When a large amount of water is suddenly encountered, it will cause underground mining and roadway flooding accidents, resulting in a large number of casualties and equipment damage. According to statistical analysis, the underground water seepage accident is one of the most serious accidents in China's underground mines. For example, on July 17, 2001, 81 people were killed in a large flooding accident at the Lajiapo Mine in Dachang Mining Area, Danxian County, Guangxi Province.
Second, the analysis of mine water filling factors
The factors of water filling in pits include: the source of water, the channel of water inflow and the factors affecting the amount of water. They are important basis for calculating water inflow, predicting water inrush, dewatering of mines and design of mine drainage.
   (1) Water source for filling the pit
Water sources filled with pits include groundwater, surface water, atmospheric precipitation, and stagnant water in abandoned mine pits.
   1. Groundwater
Some deposits and ore bodies themselves contain large voids, which are filled with groundwater, which flows directly into the pit during mining and becomes a source of water. Some ore bodies have large voids in the surrounding rock. It is full of groundwater and when it is connected to the pit, it also becomes a source of water for the pit. According to the nature of the water-containing voids, groundwater can be divided into pore water, fissure water, and karst water.
(1) Pore water is the water contained in the loose sedimentary rock and the water contained in the pores of the rock. The amount of water in this water source is generally small. This source of water is often encountered in the mining of loose deposits or minerals in close to loose deposits.
(2) Fissure water is groundwater buried in hard rock fissures. When the tunnel reveals the ore body and surrounding rock with fissure water, the fissure water will flood into the tunnel to form a mine water. If the fissure water is not connected to other water sources, the amount of water in the pit will gradually decrease or even dry up; when there is contact, it will cause a flooding accident. Compared with karst water, fissure water has a smaller amount of water inflow, but the water pressure can be high. Most of China's metal deposits are distributed with layered and veined fissure water.
(3) Karst water is water buried in a karst cave. The karst water is generally buried deep, with large water volume, high water pressure, strong momentum, stable water inflow, and difficult to drain. The law of water inrush is controlled by karst development. The distribution of karst water in China is relatively common.
   2, surface water
When mining minerals located within the influence of surface water bodies such as seas, rivers, lakes and reservoirs, under certain conditions, these waters can flow into the tunnel and become a source of water for the mine to fill or even flood the well. There are often small and medium-sized rivers, lakes and reservoirs distributed around many deposits in China. They flow through and exist on permeable pebbles with good permeability, which provides favorable conditions for surface water seepage. Most seasonal rivers have been cut off during the dry season, but the riverbed still has a large amount of groundwater, which can still serve to replenish groundwater. In studying the effects of surface water on the filling of mines, attention should be paid to the study of the relationship between formation and structure between surface water and tunnels, and the mining methods used. Surface water has a greater threat to mining. In exploration and mining, sufficient attention should be paid to surface water bodies.
   3. Atmospheric precipitation
Infiltration of atmospheric precipitation is one of the replenishing water sources for filling water in most mining areas. Mining is low-lying and shallow-buried deposits. In the absence of other water sources, atmospheric precipitation will be the main source of mine filling; mining is higher than In the valley of the valley, atmospheric precipitation will be the only source of water for the pit. Atmospheric precipitation has obvious seasonality. In the summer rainy season, mountains may form floods, threatening the safety of mine production.
   4, water in the waste mine pit
   (2) Analysis of the reasons for filling the pit
The reason for filling the pit is complicated. It is affected by the water source and the lithology, the topography and geological structure of the mining area, and human factors.
   1. Influence of geological structure and lithology on mine water filling
(1) The groundwater inflow tunnel is related to the nature of the surrounding rock exposed by the pit. As disclosed, the rock is a flowing sand layer and loose and crumb-like. When there is a fixed supply water source, the amount of water inflow is particularly large, which can cause the sand to collapse. The clay impervious layer is a favorable rock formation that isolates the adjacent aquifer. When the lithology is consistent, the pore size of the rock is uniform, so when the tunnel passes through, the water inflow is uniform. The greater the porosity, the stronger the water permeability.
(2) The various cracks in the rock formation are often the places where the groundwater is concentrated, which controls the runoff of the groundwater. When the crack is connected with other water sources, it is an important factor in the filling of the pit. Structural fissures include various joints, fissures, and large fissures, sometimes the main channel for filling the pit. Joints, especially Zhang Jieli, are the most favorable channels for filling water in mines. The joint type cracks are fine and uniform, and the water penetration is slow. Under the same conditions, the brittle rock is more developed than the soft rock, and there are more joints and the width of the crack is also large.
(3) Faults are divided into water-separated faults and water-permeable faults. The water-storing fault is mainly formed by pressure and partial torsion or later filling and cementing. It does not carry water itself, and can also cut off some water-cutting layers, which can play a beneficial role in partitioning and drying. When the water-permeable fault is hydraulically connected with other water sources, the amount of water inrush from the mine is large and stable, and it is difficult to recover. When there is no connection with other water sources, the water reserves in the fault are generally limited, and the water inrush starts to be large, and then gradually decreases or even dry up. Huge fractures often have large water cuts and are extremely harmful.
(4) The karst caves can be small pores to huge caves, can communicate with each other, form a huge underground river, can store a large amount of groundwater or communicate with other water sources. When the mining work approaches or exposes them, it is easy to cause catastrophic water.
(5) Generally, as the depth of the rock increases, the cracks of the rock gradually decrease, and the amount of water inflow gradually decreases. However, due to the pressure of the underground rock formation or the hydrostatic pressure in the ground, or the combination of them, the floor of the tunnel can be promoted. Create cracks and communicate the aquifer, water-bearing fault zone or karst water in the lower part of the bottom plate to increase the pit water or cause a water inrush accident.
   2. Influence of atmospheric precipitation and surface water body on mine water filling
(1) Due to the topography of the mining area, the depth of the burial of the ore body and the extent of the permeable base rock and the thickness of the water-repellent layer, it is easy to collect water in the swamp and low-lying areas. The mines in the site have more frequent water and surface water. Open pits and underground pits using caving mining, the catchment area of ​​atmospheric precipitation in open pits and surface subsidence areas directly determines the amount of atmospheric precipitation infiltration in the pit;
(2) Underground mining pits, atmospheric precipitation and surface water infiltration gradually decrease with the increase of mining depth. The amount of water in the pit depends on the extent of the permeable bedrock exposure and the thickness of the sub- clay and clay cover that can isolate the ore-bearing layer from the surface water. If the stable thickness of the cover layer exceeds 5 m, the groundwater can hardly penetrate downward. If there are huge passages, such as breaks and sand layers, it is prone to catastrophic water inrush;
(3) The closer the surface water body is to the pit (mineral body), the more serious the water filling, and the more serious the water in the pit. When the surface water body existing in perennial water is a gushing water source, the larger the water body, the larger and stable the water inflow from the pit. When flooding the well, it is difficult to recover; when the seasonal water body is a gushing water source, the degree of influence on the water influx of the mine varies with the season;
(4) The amount of water in the pit varies with the season and the regional precipitation. The amount of water in the rainy season is 20% to 40% larger than the average water inflow, sometimes even two or three times; the precipitation is large, and the rain is infiltrated for a long time. favorable;
(5) With the increase of mining depth, the influence of atmospheric precipitation on the water inrush in deep pits is reduced, and the peak of water inflow is delayed.
   3. The influence of human factors on the filling of mine pits
(1) Inappropriate mining methods, such as the use of caving, cause surface cracks and collapses, causing groundwater, surface water and atmospheric precipitation to flow into the pit, causing water inrush;
(2) If the exploration borehole is not closed or is not tightly closed, it will also become a channel for communicating the top of the pit, the aquifer of the floor or the surface water.