First, the basic overview of the tailings pond
Lixi tailings is Beijing Nonferrous Metallurgy Design Institute designed in 1973, in May 1977 the former Ministry of Metallurgical Industry tenth Metallurgical Construction Company began construction, September 15, 1983 according to the design completed and put people to run. The final stack dam is designed to have an elevation of 1,300 m, a total storage capacity of 165 million m3, a total dam height of 164.5 mm, and a service life of 32 years.
The initial dam of the tailings pond is a rockfill permeable dam, which is formed by directional blasting. The dam crest elevation is 1176.5m, the top length is 115.0m, the top width is 4.0m, the dam bottom is 157.0, and the dam height is 40.5m. The initial slope ratio of the initial dam is 1:1.7, the downstream slope ratio is 1:2.0, the downstream of the dam is set at a height of 1156.0m with a width of 2.0m, and the upstream is laid with a 0.7-1.0m thick filter layer to facilitate drainage and reduce the later stage. The dam wetting line is piled up, and the seepage of the dam body is returned to the reservoir through the downstream pumping station to avoid the pollution of the downstream environment by the wastewater.
In the later stage, the elevation of the dam is increased by using the upstream method to build the tailings. The height of the sub-dam is 3.0m. The loader is used to load the sedimentary beach tail sands. The tailings pipe is laid on the top of the sub-dam to disperse and release the ore. The sedimentary beach is formed by natural classification, and the dam body is formed in the later stage. The outer slope of the dam is stepped, and the designed slope ratio is 1:5. It is covered with soil-bearing gravel and has a network-like drainage intercepting ditch. At present, 26 dams have been built in the late dam. The average elevation of the dam crest is 1257m, the total dam height is 121.5m, and the final design elevation is 43m. According to the current production capacity of the plant, it can reach the final elevation of 1300m after 13 years of operation.
The tailings deposition law of tailings dam is: from the top to the bottom, it is generally tail sand, tail fine sand, tail silt, a small amount of tail sand, tail light sub-viscous and thin layer tail heavy sub-viscous, tail sand mud. The stacked dam beach surface is mainly composed of tail sand and tail fine sand, which gradually tapers into the dam and deep.
Second, the need to reduce the immersion line of the dam
In 1998, the Lixi tailings reservoir has piled up 22 sub-dams, the elevation of the dam crest is 1244m, and the height of the late accumulation dam is 67.5m. Due to the general elevation of the immersion line of the dam, more water seepage occurs at the foot of the dam, involving 2~ 12-way dams, of which 3 to 8 dams on the left bank seepage and swamping are more serious. In order to reduce the immersion line of the dam, avoid the water in the dam from overflowing the dam surface, enhance the consolidation ability of the tailings, improve the safety and stability of the dam and the ability to ferry, ensure the safe operation of the tailings dam, and decide to reduce the dam on the Lixi tailings dam. Body immersion line treatment.
Third, the program and construction
According to the specific situation of the dam body of Lixi tailings and the technical development of reducing the immersion line of the dam at home and abroad, it is decided to reduce the immersion line of the dam by using the horizontal vertical joint drainage system of the large-mouth radiation well and the drainage board. The project was designed by Beijing Nonferrous Metals Design and Research Institute and was constructed by Maanshan Changjiang Geological Engineering Company. The first phase of the project was completed from June 20 to October 9, 1998. The second phase of the project was completed from April 15 to September 6, 2000. Six wells of the large drainage well drainage board joint drainage system were built and put into operation. .
The horizontal vertical joint drainage system of the large-mouth radiation well and the drainage board is mainly composed of a large-mouth radiation well, a drainage board and a water level observation hole.
(1) Large-mouth radiation well
The large-mouth radiation well is mainly composed of a shaft, a horizontal water guiding hole and a horizontal water filtering hole.
1. Shaft
The shaft is made of reinforced concrete and sinks into a round well of a certain depth in the dam. The inner diameter is 2.9m and the outer diameter is 3.5m. It serves as a construction site for horizontal drainage holes and horizontal water guiding holes, which is connected to water seepage and drainage. . The construction of the shaft mainly includes the steps of making the wellbore, sinking the well, sealing the bottom and making the cover.
The wellbore is made by reinforced concrete for on-site pouring. At the selected well location, excavate a certain diameter (usually 5.5m) and depth (generally 1 ~ 1.7m) construction site, and then build a support model at the excavation construction site according to design requirements and specifications, the main reinforcement The inner and outer rings are entangled in a mesh shape to form a support mold, and then poured to form a first wellbore. In the first section of the well, the high-pressure water gun is used to erode and liquefy the tailings, and the sewage pump is used to discharge the sand, and the wellbore sinks at the same time, which is the sinking well. When each wellbore sinks to a certain depth, the formwork pours the second wellbore. Repeat the above work, to the depth of the well, and carry out the back cover. The back cover is firstly subjected to pre-compression and decompression to suppress sandblasting, and then the back cover is applied to the pre-fabricated pressure plate. Firstly, the hole in the well wall is drilled, and two layers of ribs are inserted. The two layers of ribs are anchored with cement mortar. The reinforced mesh is placed at the upper ribs and tied together, and concrete is poured to complete the construction of the back cover. The cover plate is prefabricated according to the diameter of the shaft, and a channel steel or a seamless steel pipe is set as a beam at the wellhead, and the cover plate is laid on the beam to complete the construction of a shaft.
2, horizontal water guiding hole
The horizontal water guiding hole is to draw the water seepage from the horizontal drainage hole in the well, and the construction is carried out from the well to the outer pipe of the dam. The diameter of the top pipe is 108mm, the length is generally about 55m (the dam body is led out), and the slope is 3%. It is usually applied before the water filter hole.
For the construction of horizontal water guiding holes, the opening height, opening position and opening direction should be determined according to the design, and then the horizontal drilling rig is used for construction. The hole of the well wall is made of alloy drill bit. When the alloy drill bit cuts through the reinforced concrete shaft wall, it is converted into a double pipe single-acting drill with a clear water slag method. While the drill bit is propelling, the casing is followed up synchronously. After the design length (out of the dam body), the drill pipe is pulled back, the drill pipe is blocked and reinforced, and the casing is left in the hole as a water conduit to complete the construction of the horizontal water guide hole. . The number of horizontal water guiding holes is generally determined according to the amount of water displacement. Generally, 1 to 2 water guiding holes can be used to meet the demand.
3, horizontal filter hole
The horizontal water filtering hole filters out the water in the dam and leads it to the shaft to reduce the infiltration line of the dam.
The water filtering hole is the top pipe from the well to the aquifer of the dam body. The diameter of the top pipe is 108mm, and the depth is generally about 60m. A water filter pipe with a diameter of 56mm and a slope of 3% is installed in the water filtering hole.
The construction of the horizontal filter hole, the construction of the water-conducting hole in the same stage in the early stage, while the drill bit advances, the casing is followed up synchronously, drilled to the design depth, the inner mouth of the casing is blocked with a plug, and the tailings in the casing are flushed with high-pressure water. Until the rinse is clean, pull out the drill pipe in the hole, lower the filter water pipe, and finally pull out the casing to seal the hole, that is, complete the construction of a horizontal water filter hole and the installation of the water filter pipe. Use the same method to complete the construction of other water filtration holes. The installation of a filter pipe in a radiation well is generally determined according to the water content of the dam. The Lixi tailings dam radiates and installs 18 water filter pipes, which are installed in two layers, 9 on each floor. The filter water pipe adopts Malaysian soft water filter pipe or FRP/PVC composite pipe.
(2) Drainage board
The PVC vertical plastic drainage board used in Lixi tailings dam has a specification of 100mm×4.5mm. The function is to penetrate the opposite water layer and communicate the upper and lower aquifers to improve the vertical penetration capability. The layout of the drainage board is mainly distributed on both sides of the middle section of the filter water pipe and the parallel dam axis according to the actual situation of the dam surface. The buried depth is about 0.5m above the buried depth of the filter water pipe.
The construction of the drainage board is made by high-pressure water rushing method. The 1.5-inch water pipe is used as a rushing gun. The high-pressure water is quickly rushed to the depth of the drainage board. The blasting gun is pulled out after the tailings in the hole are exhausted. The drainage board follows the lance. Once again, enter the hole, send water (without high-pressure water) to the bottom of the hole, pull back the punching gun, fill the coarse tailings, and fill the water to complete the construction of the vertical plastic drainage board.
(3) Water level observation hole
The water level observation hole is set as the long-term water level observation of the dam body, and is mainly distributed on the dam surface of each sub-dam.
The construction of the water level observation hole can be carried out in two ways: the shallow hole can be carried out by high pressure water rushing method, the depth is generally about 12m, and one measuring tube is installed; the deep hole is carried out by the XU-1 type rig vibration and sinking method, depth Generally, it is about 25m, and three measuring tubes are installed. The deepest one has a depth of 25m. The depths of the second and third roots are determined according to the depth of the opposite water layer in the borehole. The high-pressure water rushing method is to follow up the rushing gun synchronously, and the high-pressure water is discharged into the hole. When the hole depth is in place, the blasting gun is quickly pulled back. The measuring tube is installed, the thick tailing sand is backfilled, and the orifice is reinforced with concrete, and the number is noted. . Vibration immersed tube retaining wall method, first install the drilling tool at the hole position, use the twist drill to open the hole to find the initial water level, see the water after the casing is shaken and sink, the water in the pipe is drained, and the cycle is repeated until the hole is deep. . After the hole is formed, the measuring tube is arranged below, and the measuring tube is firstly deepest, and the thick tailings are backfilled to the depth of the second measuring tube, and the casing is shaken to the depth, and the bentonite ball is about 300 m thick, and The original water-repellent layer is integrated to block the penetration of the upper and lower water layers; the second tube is placed above the partition, and the upper layer is further provided with a partition for the third tube. After the test tube is buried, the casing is shaken. The orifice tube is reinforced with concrete, and the nozzle is tightly covered with a plug. The number of water level observation holes should also be arranged according to the changes of the immersion line of the dam.
Fourth, analysis and conclusion of drainage effect
From the seepage effect of the horizontal vertical joint drainage system of the large-mouth radiation well and the drainage board built from the Lixi tailings dam, the maximum daily drainage volume of the six radiation wells is nearly 10,000 cubic meters, and the water seepage volume gradually decreases with the passage of time. The water seepage is clear and transparent, and does not contain tailings. The dam body infiltration line generally falls below the safe water level of 6~8m. The original seepage point of the 2~12 road dam has been dry, the dam body swamping phenomenon has completely disappeared, and the dam body stability is obtained. Significant improvement. It shows that the horizontal and vertical joint drainage effect of the large-mouth radiation well and the drainage board is remarkable, and the purpose of reducing the saturation line of the tailings dam body can be achieved. The application in the Lixi tailings dam was successful.
V. Suggestions
The drainage system is established in the lower part of the dam body of Lixi tailings reservoir, and the immersion line is effectively controlled. However, as the dam body continues to rise, the immersion line of the dam will also rise, and the upper dam must also establish an drainage system. Based on the fact that the construction of the radiation well drainage system is complicated and costly, it is recommended to pre-buried the gravity drainage facilities in the dam construction process of the upper sub-dam.
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