Fan Shiyong Cui Liangzhong Ma Wen Li Xiaozhong (Anhui Geology Construction Engineering Co., Ltd.)
I. Introduction
Early domestic tailings dams and power plants use more initial ash silo clay dam, poor water permeability; post-dam (a dam) upstream of the multi-use method to build, use mine tailings, coal ash powder filling tail from rolling. In the middle and late stages of tailings storage (power plant ash storage), due to the lack or failure of drainage and drainage facilities, or due to differences in raw ore and production processes, the particle composition and permeability of various tailings and fly ash are quite different, and The existence of weak interlayers such as slime, as the accumulation surface of the reservoir area continues to rise, the immersion line of the dam will also rise. Under the action of long-term saturated water, the physico-mechanical properties of the dam body filling soil began to deteriorate, which was manifested in the beginning of seepage and swamping at the foot of the initial dam half slope and the dam dam, and then the dam surface showed different degrees of subsidence or uplift. Localized piping and other conditions.
Due to the high immersion line, the minimum safety factor is insufficient when the dam body is tested for anti-sliding stability, which is judged as sick dam, dangerous dam and dangerous dam. As for how to control such diseased dams, dangerous dams and dangerous dams, how to reduce the immersion line, the traditional method is to preset the bleed blind ditch, the drainage sluice pad and the pre-buried permeable pipe, but such pre-buried drainage facilities It was not effective at the time of completion, and it only worked until the immersion line exceeded the drainage facility, and there is a fatal disadvantage of this type of pre-buried drainage facility, that is, the drainage facility must be carried out before the dam body is increased and the construction is increased. After the pre-buried and pre-buried facilities are installed, after subsequent disturbances such as stacking and rolling, and then post-consolidation and drainage, it is very easy to cause the pre-buried drainage facilities to be ineffective or blocked. This phenomenon is very common. In addition, the traditional method can't do anything about the dam that already has too high a immersion line.
Self-flow drainage of radiation wells is an emerging engineering measure to reduce the immersion line of dams in recent years. It has the characteristics of strong adaptability, significant drainage effect, long running time and low operating cost, and has no traditional drainage efficiency and is easy to fail. And shortcomings such as blockage. The basic working principle: sinking the large-diameter reinforced concrete wellbore into the ground, constructing a horizontal filter water pipe in the well to the tailings pond (ash yard), collecting the seepage water, and using the long-distance water conduit to discharge the seepage water to achieve self-flow, achieving long-term and stable Precipitation effect.
Second, the composition and construction process of the self-flow drainage system of the radiation well
As shown in the figure, the self-flow drainage system of the radiation well consists of three parts: the shaft, the horizontal filter pipe and the horizontal water pipe. According to different dam body wetting line rise height, water accumulation in dam, degree of swamping of multi-stage dam dam surface, total length and total height of dam body and specific conditions of dams at various levels, integrated tailings (fly ash) The differences between the physical and chemical composition, as well as the parameters of the permeability of water in the dam and other factors, determine the planar arrangement and depth of the radiation well and the technical parameters of the horizontal water filter. Generally, the radiation wells are arranged on the 2~3 sub-dams with a spacing of 80~100m. The depth can reach the bottom of the initial dam.
(a) shaft
The function of the radiant wellbore is to concentrate the water infiltrated into the horizontal drainage hole into the well and then exit the dam through the horizontal water guiding hole. The shaft wellbore is made of reinforced concrete on-site, constructed by the sinking method, sub-section production, sinking by mode, and sealing the bottom after reaching the design depth.
Because the tailings (ash) has the characteristics of loose, easy liquefaction flow and sharp decrease in strength after liquefaction, the sinking method of the radiation well needs to be determined for these characteristics. Above the immersion line, the sinking method is mainly manual excavation. Below the immersion line, the undrained caisson method is used for construction, and the “sucking method†(also known as bottom liquefaction method) is the main method. When the depth of the caisson reaches 20m or more, or when it is for a complex formation, the sinking method is used to sink the well, and the depth deviation of the caisson generally has to exceed 100mm. The back cover adopts the grouting secondary sealing construction process, that is, after the sinking well is stabilized, the grouting is fixed to the well circumference, the bottom of the well is not drained, the bottom part of the well is exposed, and the lower part of the whole bottom plate is grouted again. The back-sealing process can reduce the waste of the excess part of the material than the super-sealing back cover used in the past, and the success rate of the back cover is 100%. The radiation well with a depth of 20m is designed, and all the caisson construction is completed within 40 days.
(2) Horizontal water filter
The function of the horizontal radiant filter pipe is to seep the water in the dam and introduce it into the shaft, so as to reduce the water level in the dam and the immersion line of the dam, which is the key to the entire drainage system.
The combination of “TBYH and pipe drilling method†and “PHDY horizontal filter pipe installation method†originally created by Anhui Geology and Minerals Water Conservancy and Hydropower Engineering Co., Ltd. is not only rapid in construction, but also excellent in quality and installation success rate of 100%. The working efficiency can complete the construction of the horizontal filter water pipe 50m.
(3) Horizontal water conduit
The function of the horizontal water conduit is to introduce the water seepage from the horizontal filter water pipe into the outside of the dam to realize the self-flow drainage. The construction of the water conduit from the well requires the passage of the tailings (ash) section and the initial dam section. Different media have different physical and mechanical properties and require different drilling methods. In addition to the construction method of the horizontal drainage pipe in addition to the above-mentioned horizontal drainage pipe laying construction, the following problems must be noted:
1. Construction capacity. The water conduit is generally long. According to the requirements of different dam body drainage, the radiation well should be placed far enough in the reservoir to increase the radiation well drainage range, so as to achieve better drainage effect.
2. Construction accuracy. In order to drain the drainage and collect the effluent in a concentrated manner, the water conduit must maintain a certain slope, and the outlet must reach the designated position. This requires that the trajectory of the water conduit must meet the design accuracy in both elevation and plane.
3. The disturbance is small. Due to the small initial safety reserve of the dam, less disturbance and less drilling of the annular gap will prevent the tube and dam body from being unstable during the construction period.
Third, engineering application examples and governance effects
At present, the self-flow drainage system of the radiation well has been successfully applied in many tailings dams and ash yard dams. The drainage effect can be directly observed by the naked eye and can be quantified by monitoring the saturation line data. The ideal anti-seepage effect has been achieved, and the worries of many owners have been solved, which has won unanimous praise from the owners and created good social and social impacts.
For example, the radiation well drainage project of the second sub-dam of Chengzhaigou ash field in Pingdingshan Yaomeng Power Plant is composed of 10 radiation wells with a depth of 33m. The design shaft adopts reinforced concrete structure with ç ¼ strength C25, inner diameter 3600mm and wall thickness 400mm. 4 layers of horizontal water filter pipes are arranged in the well, 9 layers per layer, arranged according to “semicircular†or “fan shapeâ€; pointing to the inside of the warehouse, the filter water pipe is 50m long. The filter water pipe adopts UPVC flower tube, the opening ratio is 11%, and the geotextile of 400g/m 2 specifications is wrapped. The horizontal water conduit is arranged at the bottom of the radiation well, and the water outlet is controlled according to the elevation of the outer slope of the dam; the water conduit is generally φ127mm steel pipe, and the hydraulic gradient of the water conduit is 2.5%. Construction began in April 2001 and was completed in August 2002. According to the monitoring and monitoring of the pressure measuring pipe arranged on the dam surface, for example, the ground elevation of the initial dam crest 0+350 station position is 224m, and the pressure measuring pipe water level is 221m in April 2001, and the 4# well starts on September 15, 2001. Drainage, measured water level-time curve is shown below:
After the radiation well system is operated, it can be clearly observed that the original seepage point disappears, the wet area of ​​the dam surface is gradually dry, and the water level of the pressure measuring tube drops rapidly below the warning immersion line, which meets the safety check requirements.
Another example is the radiation well drainage project of the tailings reservoir of Inner Mongolia Hongda Mining Co., Ltd. Before the construction of the project, the leakage of the dam surface is serious, especially the accumulation of dams, the phenomenon of fluid flow and sand flow can be seen everywhere, the dam is severely deformed, and 2 radiations are set for emergency construction. Well, well diameter 4400mm, well depth 22.3m, horizontal filter water pipe 2 layers, 11 layers per layer, single root 80m total 3500m, UPVC flower tube, open hole rate 9%, 300g/m 2 geotextile, horizontal water filter The head plastic drainage board is 4290m, and the water conduit is generally made of φ146mm steel pipe. After the radiation well was operated on November 10, 2006, the dam area water was quickly drained on the same day, and the soil erosion phenomenon disappeared. The dam crest road that could not be built is now accessible, and the saturation line has dropped by 8.2 m on average, achieving satisfactory results. . The measured water level-time curve is shown in the figure below:
In addition, the following table lists some examples of radiation well drainage system projects and application control effects that the author participated in:
project name | design unit | Main engineering features | Displacement (m 3 ) | Application governance effect |
Radiation well drainage reinforcement project of kiln ash field in Huainan Luohe Power Plant | Shaanxi Electric Power Design Institute | Radiation well 16 port, well depth 16m, radiant tube 6946m, water conduit 980m, dam outside drainage pipe 6080m | Sunrise water volume 9273m 3 | The flat-type ash field dam has high immersion line and partial collapse. After the radiation well is reinforced and reinforced, the immersion line drops by 5~8m, and it has been operating normally for 12 years. |
Radiation well drainage engineering of the second sub-dam of Chengzhaigou ash field in Pingdingshan Yaomeng Power Plant | Henan Electric Power Survey and Design Institute | 10 radiation wells, 33m deep well, 9600m radiant tube, 1550m water conduit, 5800m and 160m manhole outside the dam | Sunrise water volume 10457m 3 | In the valley type ash field dam, swamping occurs in many places, the immersion line is high, and the first stage dam has an infiltration phenomenon. After the radiation well is reinforced and reinforced, the immersion line drops by 7~9m, and the current storage capacity is increased to level 3, and the operation is performed. Good, the project won the second prize of 2006 Anhui Science and Technology Progress Award. |
Leakage treatment project for initial dam of Luosigou tailings dam | Beijing Nonferrous Metallurgy Design Institute | Radiant well 2, well depth 12m, radiant tube 3300m, water conduit 210m, plug-in board, etc. | Single well water output 798m 3 | In the valley type tailings dam, the seepage phenomenon on the dam surface is serious, and swamping occurs in many places. After the radiation well drainage and reinforcement, the swampization of the dam surface disappears rapidly, and the saturation line drops by 5~6m. The safety reserve is evaluated by the safety supervision organization. Claim. |
Iron Ridge, Liaoning Huadian Power Plant Phase II expansion project two sub Ash Yard Dam Foundation Treatment | Northeast Electric Power Design Institute | Radiation well 6 port, well depth 21m, radiant tube 6946m water conduit 600m, plastic drainage board 16406m, curtain grouting 5028m 2 | Single well water output 1198m 3 | The valley-type ash field dam, mixed fly ash layer, the dam surface after the dry block stone slope, there is still obvious infiltration phenomenon, the immersion line runs at high level, after the radiation well drainage and reinforcement, the immersion line drops 12.7m, Got a more than expected effect. |
Huili Zinc Mine Tailings leopard ditch Tail sandbar new Discharge Engineering | Zhonggang Maanshan Design Institute | Radiation well 1 port, well depth 22m, radiant tube 1780m, water conduit length 100m, vertical drainage row 2940m | Sunrise water volume 1056m 3 | The valley type tailings dam has complex terrain in the reservoir, and it is difficult to sink the radiation well. After the radiation well system is completed, the drainage effect is good, and the saturation line drops 5.6m. |
Radiation well drainage engineering of tailings reservoir of Inner Mongolia Hongda Mining Company | Anhui Engineering Investigation Institute | Radiant well 2, well depth 22.3m, radiant tube 2630m, plastic drainage board 4290m | Sunrise water volume 5256m 3 | In the hillside type tailings dam, the dam surface leaked seriously before construction, and the dam was severely deformed. After the radiation well was operated, the dam area water was quickly drained on the same day, and the immersion line decreased by 8.2 m. |
Guodian Gansu Jingyuan Power Generation Co., Ltd. Main Dam Anti-seepage Control Project | Northwest Electric Power Design Institute | There are 9 radiation wells, the well depth is 21~28m, the radiant tube is 10200m, the water conduit is 1135m, and the horizontal tube outside the dam is 880m. | Sunrise water volume 11430m 3 | The valley type tailings dam is a full-area wet slope below 1475m in the initial dam of the main dam. The seepage deformation and the running soil are serious in some sections. After the radiation well is operated, the dam surface is quickly drained, the soil stops, and the soft and wet soil on the dam surface begins to dry. The immersion line dropped by an average of 11.6m. |
Jiangxi Copper Silver Mine tailings rectification works | Maanshan Mine Engineering Survey and Design Company | One radiation well, the depth of the well is 15m, the radiant tube is 1357m, the water conduit is 245m, and the horizontal tube outside the dam is 346m. | Sunrise water volume 765m 3 | In the valley type tailings dam, the drainage facilities are located at the +82m platform on the south side of the main dam and the toe of the 3# auxiliary dam. The immersion line overflows and the swamp is formed. After the radiation well is operated, the immersion line drops by 7.7m on average. |
It can be seen from the above application examples that the self-flow drainage technology of the radiation well has an unparalleled advantage in dam seepage reduction compared with the traditional dialysis method or other dam reinforcement technology.
Fourth, the conclusion
(1) The self-flow drainage of the radiation well is applied to the precipitation reinforcement of the tailings dam (power plant ash dam), which can effectively reduce the infiltration curve of the dam body, and the effect is remarkable, and the stable seepage can be maintained for a long time, and the post-management work is simple.
(2) The development of caisson depth and horizontal duct length construction capability, so that the radiation well can be freely arranged in the dam area and the reservoir area, which enhances the adaptability of the radiation well self-flow drainage system and expands the drainage range.
(3) The direction of the horizontal filter water pipe is not subject to any restrictions. The filter water pipe has a wide radiation surface, a large water collection range, and a large amount of drainage. A multi-layer horizontal filter water pipe can be laid in each shaft, which can increase the displacement of the dam body with large storage capacity, high accumulation and high saturation line, and effectively reduce the immersion line of the dam body.
(4) In order to enhance the effect of drainage, a three-dimensional drainage system with vertical drainage and horizontal drainage can be used. The plastic drainage board used for vertical drainage can penetrate the opposite water layer and communicate the upper and lower aquifers to improve the vertical penetration ability. The drainage board is buried in the middle of the middle section of the filter tube and in the direction of the parallel dam axis, and the buried depth is about 0.5 m in the upper part of the horizontal filter water pipe.
(5) The wellbore of the radiation well can be increased with the heightening of the dam, and a horizontal filter water pipe is added in the well to increase the efficiency of use of the radiation well and save investment.
(6) The diameter of the radiation well should not be reduced, otherwise the volume of the drilling machine will be limited, thus affecting the drilling performance. Large-diameter horizontal water pipes and water pipes are also a guarantee to prevent blockage. From the engineering practice point of view, the self-flow drainage system of the radiation well constructed by our company has been running for 12 years, and no clogging phenomenon has occurred.
(7) The seepage deformation and damage of the dam body is caused by the improper control of groundwater in the dam, especially the implementation of the heightening and expansion project, so that the infiltration curve of the whole dam body continues to rise. If there is no suitable precipitation drainage measures, it will inevitably lead to instability such as erosion, piping, slippage and swamping on the dam surface. Radiation well self-flow drainage measures should be designed and constructed at the same time as the heightening project of the dam body to avoid precipitation after the danger of the dam body.
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