Building a flood control ditch

Located in the foothills or piedmont region of metal ore and coal mines, within its mining area, no more large surface waters become a major source of water in water-filled mine. Atmospheric precipitation in mountain mines is often diverted into the recharge aquifer in the form of flash floods or subsurface flows, or into the mine from subsided areas or fissures caused by mining. If the wellhead location is not properly selected and is below the highest flood level, there is a danger of direct flooding of the mountain torrent into the wellhead.

First, build an example of flood control ditch

In Huainan Datong Coal Mine, the stratigraphic trend is consistent with the trend of the hillside, and the limestone karst is developed. Due to the long-term large-scale drainage, large-scale settlement belts and collapse pits with a length of several kilometers appear along the mountain front. When the rainwater mine has a large amount of water in the rainy season, the row is inferior. . In order to prevent the floods from flowing into the subsidence and subsidence zone, the mine excavated a flood-stricken flood-control ditch that was several kilometers long in the direction of the incoming water, so that the mountain floods leaked out of the wells along the ditch, avoiding the hazards of flash floods.

The No. 8 well of Xibo Mine in Zibo is in a hilly area, and the rainwater flows down the hillside to the low depression to replenish the mine. In order to prevent floods and reduce the amount of water in the mine, the mine excavated a hydrophobic network composed of large and small ditches according to the terrain, and introduced rainwater into the hydrophobic ditch at the foot of the mountain and led it out of the boundary. The effect was remarkable.

Second, the location of the flood control ditch

The choice of the position of the flood control ditch is the key to the success of the mine ground waterproofing project. The principle of land selection for flood control ditch should be:

1 Try not to change the natural flow direction;

2 Try to use existing or artificial existing ditches and terrain;

3 The radius of curvature of the flood control ditch shall not be less than 5 to 10 times the width of the ditch;

4 to be placed outside the mine or minefield;

5 The flood control ditch should avoid the aquifer outcrop area, fault fracture zone and karst development zone related to mine water filling. If it is necessary to cross the above zone, the flood control ditch shall be treated as anti-seepage;

6 The flood control ditch line should be selected with good engineering geological conditions, no slopes with landslides and landslides, and a relatively solid zone.

7 The flood collection range should be able to maximize the pooling of floods into the mine.

Third, the section and slope of the flood control ditch, slope

The section size of the flood control ditch shall be based on the maximum flash flood that can be quickly discharged during the rainy season. It is necessary to understand the maximum flood amount in the mining area over the years, calculate the maximum design flow, and find the optimal section.

The slope of the flood control ditch should be roughly consistent with the slope of the terrain. In areas where the terrain is too steep, to prevent over-flow and cause erosion, a water-dropping facility can be installed.

The slope of the flood control ditch shall be determined according to the engineering geological conditions of the design route and the condition of the retaining.

Block the passage and drain the water

1. Blocking pits and cracks

After the ore is mined, a goaf is formed underground, the overlying rock loses its support, and the roof moves, deforms, and ruptures, causing a large area to fall. As the mining area expands, the rock layer moves and sinks to the surface, forming a subsidence basin. Collapse pits and cracks. These are atmospheric and surface water irrigation channels.

For example, the Huainan Mining Bureau Jiulonggang Mine, due to the reverse of the strata, the limestone of the Taiyuan Formation of the Carboniferous is overlaid on the coal seam. After the coal seam is mined, the limestone of the roof is quilted, and the shape is like a stack of tiles. The vertical stratum is distributed, and the width is more than 1000 m. The degree of opening is enormous. Some mine roof cracks communicate with the original karst fissures and karst caves, and up to the surface, become channels for atmospheric precipitation and surface water to enter the well. In the steeply inclined metal mine, not only the roof will fall, but it will cause collapse and quilting, and sometimes there will be similar passages in the direction of the bottom plate.

Methods for sealing pits and cracks are as follows:

1 Bring the flood out of the collapse zone

In addition to setting the flood control ditch to prevent floods from entering the collapsed fracture zone, the precipitation in the subsidence zone should be led out of the mine in time. To this end, the intercepting water ditches can be excavated in the periphery of the collapsed fracture zone, and the water ditches can be opened in the subsidence area, and the precipitation can be concentrated to the section that does not leak into the underground, and then the mining area is led out.

2 Filling collapse pits and cracks

The method of filling the pit with soil and stone is that the lower part is first filled with stones, waste rock and vermiculite , and the upper part is covered with soil and clay , and layered and compacted to make it 0.5m~1m above the ground.

3 Enclosure isolation collapse zone

When it is impossible to backfill the subsidence group in the floodplain, it can be segregated by the earth embankment to prevent flood flooding.

Lead-zinc mine in Hunan Shuikoushan this method to isolate a large bridge collapse area was home; Hunan mountain hats, uh mouth and other coal mines have received this method ground water effects.

Second, discharge surface water

Atmospheric precipitation accumulates on the surface of the mining area, forming surface water bodies. When this water accumulates in the mining area, the surface soil layer is thin, the water permeability is strong, and the shallow limestone karst is developed, the water source of the mine water filling will be formed and should be discharged as soon as possible. The discharge of surface water must be based on the specific conditions of the mining area, and a reliable and reliable method of discharge must be selected.

1 Self-flow drainage should be preferred if conditions permit. That is, the drainage ditch is opened from the stagnant water area, and the water is led outside the mining area. Before excavating the drainage ditch, it is necessary to carry out on-site survey beforehand, select the ditch line and slope, and then determine the shape and size of the section by hydraulic calculation.

2 Construction of pumping station; mechanical drainage. If there is no self-flowing drainage condition, a pumping station must be built to drain the accumulated water.

There are two types of pump stations: temporary pump stations and permanent pump stations. Temporary pumping stations are established during the rainy season and are removed after use; permanent pumping stations are used for long-term use after establishment. The drainage capacity, displacement and drainage time of the pumping station, terrain conditions, equipment utilization, etc. are the basis for considering which pump station is constructed.

Exclusion of water must prevent backfilling and backflow. Therefore, it is necessary to send the excluded water as far as possible away from the stagnant water area or away from other places that may penetrate into the well, and the ditches along the way should take anti-seepage measures.

If the water accumulation is not large, the water is not deep, and the material is convenient to be taken nearby, after the water is discharged, the clay can be filled and tamped with clay to prevent water from accumulating again.

Riverbed or river diversion

First, the riverbed bottom

When surface water systems such as rivers and ditches flow through the fault zone of the mining area or the outcrop of the limestone aquifer, the river water may be lost along the bottom of the riverbed or ditches and infiltrated into the well to become the water source for the mine to fill.

In the case of unsuitable diversion, the riverbed can be laid in the leaky section at the bottom of the riverbed or ditch, and the riverbed should be laid with a leak-proof and anti-seepage material, such as clay, stone or cement, to prevent the river from seeping down the well. leak.

Issues to be aware of when constructing artificial riverbeds:

1 To carry out hydraulic calculations, determine the section of the new riverbed, but the section of the original riverbed should not be reduced too much;

2 In-situ materials, construction of leak-proof and anti-seepage layers, should also meet the requirements of anti-corrosion and anti-scouring;

3 For sand and pebble riverbeds, they cannot be built with rigid materials because they are easily deformed;

4 When pouring concrete on the bedrock, pay attention to the clearing;

5 In the northern mining area, pay attention to antifreeze;

6 For riverbeds with water leakage on the bank slope, the bank slope should be lining the same at the same time as the bottom of the bed.

After the artificial riverbed was built in a mine in Nantong, Sichuan, the water inflow in the rainy season was reduced by 30% to 50%. The Jingxi coal mine had a 4.4 km long ditches with serious leakage. After artificial laying, the ditches were basically removed from the well; Xinbo Mine In Well No. 1, there is a perennial river channel called Xiaofu River passing through the center of the mine field. After the river bed is laid, the average annual water inflow of the mine is reduced by 30%.

Second, the river diversion

The river flowing through the mining area, if there is a karst aquifer below it, and there are many cracks at the bottom of the river. When it is not suitable to construct an artificial riverbed, the river should be diverted, that is, the river is led out of the mining area by artificial river.

1 Change the road line. The new river channel has the shortest distance requirement; the new river channel should avoid going uphill and avoid unstable soil layers or severely exposed strata as much as possible; the new water road line should take into account the prevention and control of water, mine prospects, agriculture and environment.

2 The choice of starting and ending points of the new river. The starting point should be used to induce the river to flow into the new river; the starting point should be selected in a stable section that is not easily washed away; the intersection of the end point of the new river and the original river should not be too large to avoid scouring the river bank; the starting point of the new river, the original channel Upstream, a barrage should be set to introduce water into the new river; a distance should be kept between the barrage and the starting point of the new river to prevent the barrage from being flooded.

3 Old river courses must be disposed of. In order to prevent the hidden dangers caused by the old rivers, the old rivers must be drained first, and then the clay and meteorites should be filled in, and the old rivers will be converted into good fields, which can prevent rainwater from accumulating and increase profits. Remove silt deposits when necessary.

4 Partially bend and straighten to reduce the flow of river water through the mining area; use artificial drainage to lead the river water in the mine to the lower mine. These two methods do not have to be completely diverted, only partial adjustments.

Fill the old kiln wellhead

China has a long history of mining. Some old mining areas have old kiln, ancient pits are densely covered, and old kiln is mostly distributed near the outcrop or at the shovel, causing rainwater to accumulate. The old kiln well is deep in water, and there is potential pressure in the deep mining area. Once the water is bursting, the pressure is high and the casualties are heavy.

Closing these old kiln wellheads should be investigated, plotted, and marked afterwards. The large wellhead can be closed with a cement cover, and then covered with loess; shallow and small old pits can be directly filled with soil near the old kiln wellhead; for the wellhead near the river ditch, 1m thick lime soil should be covered and the wellhead should be high Above the ground more than 1 meter.

The wellbore in the farmland should be filled with 37 soils with a thickness of not less than 1 meter at a distance of 2 meters below the surface, and then covered with arable soil. This will prevent leakage of rainwater and prevent the cultivation.

Located on the hillside of the ancient kiln wellhead, a circular retaining wall with a height of not less than 1 m can be used to intercept the rainwater.

In addition to the ancient kiln old pit, the mining area should also pay attention to the abandoned tunnels and wellheads of townships, individual small coal mines or folk metal mines in recent years.

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