Underground mines that are mined by the open field method or the caving method often form huge underground goafs and caving areas. When the area of ​​the goaf reaches a certain number, large-scale sudden collapse and other geostresses may occur. , causing significant losses to people and property. A large number of mine accidents have shown that the treatment of goaf is not timely, the improper selection of mining methods is mixed with multiple mining methods of the same ore body, the pillars are not enough, and the roof is not fully collapsed. source. The essence of the goaf treatment is the location of the concentrated or transferred stress concentration, which reduces the stress concentration of the rock mass and makes the stress reach the relative balance again, so as to control and manage the ground pressure to ensure the safe production of the mine.
Appropriate selection of the treatment method of the goaf should take into account the specific conditions of the mine, such as geological conditions, mining methods, spatial status, and ground pressure characteristics. After careful analysis, the safety measures are proposed in a targeted manner. This paper takes the measures of treating an emptying area in an underground mine in Hubei as an example.
1 Domestic goaf treatment technical methods
The technical methods for treatment of goaf in domestic mines are summarized as follows: caving surrounding rock treatment empty area, filling filling filling area, pillar supporting empty area, closed and isolated processing empty area and combined method processing empty area [1].
1.1 Caving surrounding rock treatment empty area
The feature of the caving surrounding rock treatment empty area is that the medium-deep hole, deep hole or chamber blasting method is used to form a large amount of surrounding rock in the empty area to form a cushioning protective cushion, and at the same time fill the empty area, thereby preventing the rock from being suddenly caused by the empty area. Falling and causing harm. The use of caving surrounding rock to treat empty areas can eliminate empty fields in time, relieve stress over-concentration and avoid large-scale ground pressure activities, and the treatment process is relatively simple, which can effectively improve labor productivity. This method is widely used in domestic mines.
1.2 Filling and filling treatment empty area
The filling area is filled with gravel, tailings sand, water sand, concrete, etc., so that the filling body supports the empty area and controls the ground pressure activity. The method can reduce the surface subsidence of the upper part of the ore body, prevent the fire in the ore rock, and reduce the loss and depletion.
1.3 Retain permanent pillars or construct artificial stone columns to treat empty areas
The permanent mining pillars or artificial stone columns are used to treat the goaf, which is generally used for gently tilting the ore body below the medium to thick thickness, and using the room column method and the comprehensive method to recover the roof, the roof is quite stable, and the surface allows the falling mine. The production practice of non-ferrous mines in China shows that some gently inclined ore bodies, especially the ore-rock conditions are good, and the ore bodies are selected to retain proper ore bodies, and the continuous empty area is not too large.
1.4 closed and isolated processing empty area
Closing and isolating the goaf is an economical and simple method. The purpose of closing such goafs is mainly to prevent the damage of air shock waves to people and equipment when the surrounding rock suddenly falls. Main measures for closed isolation:
(1) A roadway that connects the open space to the outside world. The method includes: constructing a reinforced concrete wall of 1 to 2.5 m thick in the roadway as a closed wall; picking the top plate in the roadway, causing the top plate to explode a layer of rock to block the roadway, and the blockage length is about 15 m.
(2) The isolation layer is provided to separate the upper empty area from the lower working area.
(3) Open the “skylight†leading to the surface in the upper part of the closed and isolated space, and then close all the passages leading to the production area and the main tunnel with a solid closed wall, so that when the surrounding rock falls, the air in the empty area is “skylight†"The flow to the surface does not become a high-pressure airflow that endangers the safety of production personnel and equipment.
1.5 joint method for processing empty areas
The combined method of treating empty areas refers to the simultaneous use of two methods to treat goafs in a goaf, including: joint support and filling method, closed isolation and collapse of surrounding rock.
2 Hazard analysis after the safety demonstration of a mined area in a mine in Hubei
A mine in Hubei has been mining with a bottomless shallow hole retention method, leaving a 6-8 m top and bottom column. After years of mining, a goaf of about 66.8×104 m3 has been formed underground, and the shallowest part of the goaf from the ground has been formed. About 50m, there is no sign of collapse on the ground. The mine is divided into the I ore belt and the II ore belt. At present, the main mining area is the II belt in the mining area. The II ore belt includes three ore bodies such as VI, VII, and VIII. The middle section that has been formed underground is: +50,0,-50,-100,-150,-225,-250,-280 and - 320m, currently the main production segment is -280, -320m is under development.
According to the occurrence characteristics of the mine, based on the on-site engineering geological survey, indoor rock mechanics test, rock mass quality evaluation, rock mass mechanical parameters determination, using Mathews stability diagram method, finite element analysis method, buffer layer thickness analysis, prevention Technical methods such as stability check of closed wall caused by sudden impact of air shock waves on the roof, a comprehensive safety demonstration of the goaf of the mine [2~5].
2.1 Goaf ground subsidence
According to the finite element analysis of the stability of the goaf, under the action of shear stress and tensile stress, especially when the span of the top column is large, it is possible to start from local collapse. If the top column is broken and the goaf is not filled, the upper and lower plates of the goaf will lose support, which will cause a large collapse of the ground. Refer to similar production mines, ore bodies
The moving misalignment angle of the upper and lower discs is selected to be 65°, thereby delineating the range of displacement during mining.
2.2 Destruction of the upper and lower plates and the top column in the goaf
According to the analysis of the stability of the goaf, the basic conclusions are:
(1) The stability of the current mining situation is good, and the scope of mining impact is limited to the range of 3 to 15 m around the goaf. At present, no large ground pressure disaster will occur.
(2) When the span of the top column ore is below 10m (the average thickness of the ore body is 6.33m), the top column is safe; but when the span of the ore body is more than 15m, the stable range of the exposed area is controlled within 600~9002m. If the exposed area exceeds this control range, the roof will gradually fall naturally; the marble and diorite will be stable and allow a large exposed area. Under normal circumstances, large areas will not fall.
(3) The interaction between the ore bodies of VI, VII and VIII is not significant.
(4) For the main mined VI body, the stress concentration zone formed by the mining disturbance is generally at the top and bottom of the goaf, and the degree of stress concentration will increase as the depth increases. At the same time of mining, a shear failure zone is formed in the range of 3 to 15 m in the upper and lower sections of the gob, and a tensile failure zone is formed in the range of 1 to 3 m. A stress concentration zone is formed in the top pillar, and the displacement formed by the mining disturbance is also directed to the mining. Empty area. Therefore, the stability of the mined area of ​​the mine is generally good, and the part of the top pillar with a large span (span > 10m) has tensile and shear failure, especially in the lower disc position.
2.3 Air shock wave hazard
The mine is used to prevent the sudden collapse of the rock formation. It is sealed with C25 concrete or red brick and steel plate at the roadway connecting the middle section of the underground with +50,0,-100,-150,-200m and the goaf. The thickness of C25 concrete sealing wall is more than 1m, which plays a certain role in preventing the damage of air shock wave. The ore body of -200mVI is close to the east and east, and is filled with waste rock, and the highest point reaches -150m.
2.4 Water inrush and flooding hazards
At present, the main mining of the mine is the No. VI, No. VII and No. VIII ore bodies in the II belt of the mining area. The northern part of the mining area has more and larger caves, which are connected with the Zhaojiagang in the lower reaches of the Qingshan Reservoir nearby, but in the II belt and I. There is a water barrier between the belts to separate the two belts safely. The II ore belt is located in an east-west long strip hydrogeological unit. The hydrogeological unit has the shale of the Silurian and the unweathered magmatic rock. The range and intensity of the atmospheric precipitation are not large, the groundwater discharge is smooth, and the underground water inflow is extremely small. Although the hydrogeological conditions of the mine should be of a simple type, if the aquifer between the I belt and the II belt is damaged during the mining operation, it will cause a sudden collapse of the underground and cause the mine to suffer. Huge loss. In addition, there are old cockroaches in the upper part of the mine, the area of ​​the empty area is large, and the water accumulation in various sections is unclear. Therefore, measures to prevent water inrush from the old mandarin and the goaf should be taken during the mining process.
3 safety technical measures
3.1 Safety measures for ground collapse in goaf
(1) Surface facilities and buildings are arranged outside the mining boundary.
(2) Strengthen the management of the subsidence area, mark the boundary line of the collapsed area as accurately as possible, and establish obvious signs.
(3) Timely grasp the changes of the goaf and timely compile the underground and ground map of the subsidence area.
(4) The necessary observation points should be buried around the surface subsidence area, and regular observations should be made to provide scientific basis for the safety management of the subsidence area, the reconstruction of surrounding roads and the early land acquisition in the subsidence area.
(5) A water intercepting ditch or a retaining wall must be installed around the surface collapse and crack zone to prevent atmospheric precipitation from penetrating into the well.
(6) Technical management of hydrogeology (flood prevention and drainage) in subsidence areas should be done.
(7) Responsible for special personnel, regularly notify the neighboring villages in writing, and pay attention to the subsidence area to prevent accidents of people and animals.
(8) The safety production management department shall regularly organize relevant personnel to supervise and inspect the safety management work and safety of the subsidence area, and propose rectification opinions.
3.2 Safety technical measures for the treatment of goaf
(1) Use waste rock or tailings to fill the empty area in time: use waste rock or tailings mined in the underground as filling material to treat the goaf. The thickness of the waste rock layer should meet the requirements of the impact buffer layer thickness. A large number of engineering practice certificates, using filling to treat goaf is the best way to control the stability of goaf. This method is the preferred solution for the treatment of the goaf of the mine.
(2) Actively collapse the surrounding rock, form a cushioning rock cushion, and treat the goaf: This method is to force the caving of the surrounding rock by blasting when the surrounding rock is stable, the integrity is good, and it cannot be naturally collapsed. The area or the formation of a cushioning rock cushion to control the pressure transfer or alleviate the stress concentration of the roof, prevent the sudden collapse of a large area of ​​the surrounding rock, and the generated air waves cause damage to the roadway, equipment and human body in the production area. Compared with the filling and processing goaf, this method is simple and easy, and the cost is generally low. The caving work on the surrounding rock of the goaf is carried out after a large amount of ore mining in the stope, which can reduce the depletion of ore loss. However, when the caving is to be placed, the differential blasting technology should be adopted to minimize the damage of the blasting shock wave to the upper top column. The thickness of the buffer layer formed by the topping should be more than 10m. If the top column collapses, the thickness of the buffer layer should be appropriately increased according to the number of collapsed middle sections, that is, a buffer layer with an additional 10m height is added. This method is chosen for use in local locations.
(3) Strictly adopt the stope structure parameters of the selected shallow hole mining and mining method, retain and maintain sufficient size of the top column and the inter-column, adhere to a reasonable mining sequence, and reasonably determine the shape and size of the roadway section.
(4) According to the stability of surrounding rock at the roadway and mining site, measures such as bolt support are adopted for the roadway and the top column, especially the top column after the span of the goaf is more than 10m, and the first is to be strengthened by bolts. Second, in its lower part, it should be reserved for its supporting pillars.
(5) Establish monitoring and observation points (net) of mining site pressure, and keep abreast of changes in mining site pressure.
(6) Strengthen the on-site inspection of personnel and timely understand the safety status of the goaf.
(7) Strengthen the management of the roof, do a good job in the inspection and treatment of pumice , and timely lick the hair.
(8) Establish safety technical operation procedures and operating systems, strengthen safety technical training, and improve the technical quality of employees.
(9) In the lanes of frequent pedestrians, people should be inspected every day. For the tops and the loose areas, they should be knocked out and asked for treatment in time. Warning signs are set up in dangerous places, and personnel are strictly forbidden to enter.
3.3 Technical measures to prevent air shock wave damage
(1) Using the surrounding rock surrounding rock or artificial filling method, a buffer layer of 10 m or more is formed in the goaf. If the top column collapses, the thickness of the buffer layer should be appropriately increased according to the number of collapsed middle sections, that is, the height of the middle section should be increased. Add 10m more buffer layer.
(2) The concrete is blocked in time in the roadway connected to the goaf, and the thickness of the sealed C25 concrete is more than 1m.
3.4 Safety measures against water inrush
(1) The safety requirements GB16423-2006 "metal and nonmetal mine safety regulations", according to the design of mining was finally determined sufficiently reliable drainage system capacity.
(2) Adopting the mining sequence from south to north, gradually approaching the I ore belt, and timely filling and filling the goaf left after the end of the mining.
(3) A flood interception ditch shall be provided around the expected subsidence zone. The drainage ditch on the surface should form a system, which should be inspected regularly and dredged.
(4) Adhere to the principle of “doubt must be explored, first explore and then excavateâ€, compile water exploration design, and strictly implement technical measures for water safety. In order to ensure the safety of the roadway construction, advanced water exploration or local grouting and water shutoff measures should be taken in the vicinity of the aquifer karst cave development or contact belt to prevent sudden water inrush during the tunneling process. In the case of an aquifer, the technician should be reported in time and the water hole should be advanced.
(5) The water gate of the main shaft and blind shaft should be inspected and tested frequently. The waterproof gate should adopt a single door and double section of 1.0MPa.
(6) When excavating new mining projects, emergency plans for emergency construction of new and old tunnels to create water inrush accidents should be prepared.
4 Conclusion
Since all types of goaf processing methods have their specific applicable conditions, each has its own advantages and disadvantages. Therefore, in order to make the treatment of the goaf corresponding to the maximum development of the underground resources of the mine, the countermeasures for the safe treatment of the goaf should be based on the safety demonstration of the gob of the specific mine. Safety hazard analysis is presented in a targeted manner.
references:
[1] Li Junping, Qian Xinming, Zheng Zhaoqiang. Research progress in the treatment of goaf [J]. China Molybdenum Industry, 2002, (3): 10 ~ 15.
[2]Chen Jingang, Li Aibing. Research on Stability Analysis of a Goaf[J]. Mining Technology, 2009, (3): 37~39, 46.
[3] Liu Zhengyu, Li Aibing, Zo Ping, et al. Stability demonstration of goaf in a mine in Hubei[J]. Mining Research and Development, 2009, (3): 62~64, 88.
[4]JI Huilong, HOU Kepeng, ZHANG Chengliang, et al. Prediction of the risk of roof caving in large goaf[J]. Mining Technology, 2010, (3): 50~54, 76.
[5] Silver Yellow Sea, Tao Discussion strict countermeasures goaf Yichang phosphate mine [J] Mining Technology, 2009, (6): 55 ~ 56, 59
Article source: Mining Technology 2010, 10 (4)
Author: Sha Luo Yi, Yao Zhen Gong; Changsha Institute of Mining Research, Changsha 410012
Copyright:
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