I. Overview
In order to extract ore from the depth of the underground, mining projects such as wells, diverticulum and stope must be excavated in the rock mass, and the stope is the main site of underground mining work. Once excavated, the original rock mass will be destroyed. Relatively balanced state, the stress of the part of the rock mass surrounding the stope (surrounding rock) is redistributed, causing deformation, destruction and collapse of the surrounding rock. Severe ground pressure will inevitably affect the normal operation of the mining work and even endanger people. life safety.
Tin mines have had many painful lessons in mining history. Before the founding of the People's Republic of China, there was no formal mining method, and the rich and the poor were abandoned, and the scale of the empty field was different. In the ore-rich area, the empty field is several kilometers long, up to more than 30 meters. In the mining process, the stope has no control measures, so the loss of mineral resources is large, the roof accident is frequent, and the miners suffer heavy casualties. According to historical records, in 1933, there were more than 100 miners who died in the mine. After the founding of the People's Republic of China, the tin mine used the formal room-column mining method. By 1965, the size of the goaf was increasing. Many of the mining areas were connected into a large area, and they were not processed in time. The time was increasing, resulting in a sharp movement of ground pressure. Three large-scale ground pressure activities caused the roof of the roadway and the goaf to collapse, the pillars to break, the rock layers to move, the surface to crack and sink, which brought serious harm to the normal production and safety of the tin mine. Therefore, it is extremely important to strengthen the management of the roof of the stope.
In order to control the pressure of the mining site and stabilize the roof of the stope to ensure normal production, we must master the laws of stress state, deformation, movement and destruction of the surrounding rock of the stope, adopt stope support, empty area treatment, stop roof, monitoring, etc. Engineering measures to achieve the purpose of controlling the roof of the stope and protecting the roof of the stope.
Second, stop support
There are many ways to protect the top of the tin mine. The ore is mainly supported by the natural support of the ore. The roof is kept with 0.8~1.2m thick ore to protect the roof. At the same time, it is supplemented by bolt support, spray support and spray anchor support.
(A) a metal wedge bolt overhead guard Feng formula
In November 1962, the metal wedge-type anchor roof was tested. After 1964, this method was widely applied. The bolt consists of four parts: the rod body, the wedge, the pallet and the nut. The rod length is 1.8m and the diameter is 1.8m. 26mm, wedge thickness 23mm, installation netness 1x1 square meters, the pole column installation and the working face rock drilling at the same time, using the vertical drilling of the vertical drilling rig , then the wedge and the pole with the pallet nut are not biased Feed into the bottom of the hole without any reliance, and tighten the nut with the drill , tighten the nut to ensure that the pole has a prestress of 2.5 to 3 tons.
With this anchor XIKUANGSHAN successfully mined STRATA f = thin layer 3-6 thick gently inclined ore body to the average return rate of 11 to 20% simple structure, easy processing, a large number of their own can Production, high anchoring force, an average of 12 to 14 tons, up to 20 tons. Use this anchor instead of the mine roof. It is technically feasible. The problem is that it consumes more steel. At the same time, because the anchor rod is anchored to the rock, the rock layer around the zone where the joint crack is more developed is easy to fall off, thus reducing or Lose the force on the rock formation.
(2) wedge-type anchor protection
In view of the shortcomings of the metal wedge-type anchor, in 1982, the tin mine and the Changsha Mine Research Institute cooperated to develop a metal wedge-type anchor. In 1983, the industrial experiment was officially carried out and then used in the mining and selection plant.
The function of the bolt is the anchoring action of the upper part of the starting point, and the lower part acts as the friction anchoring. It consists of six parts: the upper and lower wedges, the positioning pin, the retaining ring and the backing plate of the retaining pipe. The total length is 2m. Selection of coal pipe 1 inch water pipe for anchors, anchor length 1m top section, wherein the wedge 0.1M length, the lower end of the wedge thickness 1.5cm, a thickness of the lower end of the lower wedge 2.5cm.
The pole installation can be carried out simultaneously with the drilling of the working face. The drill bit with a diameter of 2 mm smaller than the diameter of the stern pipe is used. After the 2 m deep hole is drilled with the upward boring machine, the anchor of the ferrule is inserted into the hole freely, and then The drilling rig is used to press the rod with the impactor, and then the steel pin that is slightly longer than the rod is used to break the locating pin, forcing the lower wedge to squeeze and increasing the superimposed thickness of the two wedges, so as to achieve the purpose of expanding the anchoring rock layer by the top anchor tube wall. Complete the installation task.
This kind of bolt function is superior to the wedge-type anchor. It can not only expand and anchor with double wedges, but also exert frictional anchoring effect, and has strong ability to prevent the displacement of surrounding rock. The measured anchoring force averages 10 to 12 tons, which can meet the requirements of roof protection. The biggest advantage is that it consumes less than 5 kg of steel for each set of wedge-type anchors, reducing the cost by about 35%. However, it is prone to rust and is not suitable for supporting projects with a long service life. In addition, the friction section has a slow anchoring effect, which is unfavorable for timely protection.
(3) Metal pipe truss anchor protection
The tin mine south mine also used a tubular bolt support roof. The bolt length is 1.8m, the diameter is 39mm, and the pipe body is 15mm wide. The drill bit is drilled with a diameter less than 1~3mm. It can be tightened with the top drill, and the anchoring force can reach more than 10 tons. It has been widely used in the South Mine.
Because this kind of anchor is used to strengthen the roof by using the tension of the manifold and the friction of the rock. Therefore, the drilling requirements are extremely strict, the size of the drill hole, the installation of the bolt is difficult, the drilling is too large, and the reinforcement is not achieved.
(4) Cement powder anchor support
In 1990, Nanfang introduced the patented technology of cement powder anchors. Firstly, the cement powder trials were carried out in the mechanical repairing plant. After the trial production was successful, the field test was carried out in the South Mine for nearly two months, and the success was achieved. Currently, the anchor Has been widely promoted and applied in the South Mine.
The anchor rod is composed of rebar, cement quick-setting medicine roll and pad. The length of the medicine roll is 230mm, the diameter is 32mm, the weight is 185g per roll, the diameter of the rebar is 16mm, the length is 2m, and the specification of the pad is 150mm×150mm×6m.m. .
The bolt installation can be carried out simultaneously with the working face rock drilling. The drill hole is drilled with a diameter of 36mm~38mm, the hole depth is 2m, and 9~10 pieces of the medicine roll are used for each hole. After the hole is finished, the bolt is installed. Put the medicine roll in the bucket every 20s and soak it in water. After immersing for 30s~100s (according to the factory instructions of the medicine roll, when the water is immersed in the batch), take the medicine roll and immediately put it into the hole with the gun stick. Use force to prevent the medicine roll from slipping. After the medicine roll is installed, insert the threaded steel into the bottom of the hole by hand. If it is not in place, put the punch and the guide tube into the hole with the drill. If it is necessary to install the backing plate, the rebar with the retaining ring welded at the lower end should be used, and the backing plate should be placed on the rebar in advance.
The cement powder anchor rod is viewed from the anchoring function: it is a full-length bonded rock mass and has the same function as the mortar anchor. But the action time is faster than the mortar anchor. After 60min, the anchoring force can reach 6-9 tons, which is very adaptable to rocks. The effect of preventing the displacement of surrounding rock is better than that of anchoring anchors. Generally, it can be adapted except for the extremely broken rock.
(5) Shotcrete and spray anchor protection
The mining face is mined by the common room column method and the cement filling method, and the top plate is protected by ore of 0.8 to 1.2 m thick. If the mining height is more than 10m and the roof is relatively stable, the mining site is purely sprayed and reinforced. When the roof is exposed to shale , the spray anchor is used for joint support. The spray thickness is 50mm, and the bolt length is 1×1m. ~2m.
The shotcrete uses a 2Hp-2 rotary disc sprayer. 400# Portland cement, medium or coarse grain river sand and adding a certain proportion of quick-setting agent, the ratio of sand to sand is 1:3～1:4, the equipment is generally placed in the ventilation or filling roadway at the upper end of the stope, concrete The plastic pipe is sent to the stope with wind power.
Third, empty area processing
Under normal circumstances, when the mining depth is not too large, although the ground pressure increases with the increase of depth, the performance is not obvious. As the mining depth is larger, when the empty area exceeds a certain limit, large-scale ground pressure activities are often caused. , causing natural collapse in the roadway and empty area, sudden collapse of the pillar, movement of the rock formation, sinking of the surface, collapse and other ground pressure phenomena. In this regard, the mine generally uses "collapse" or "charge" to eliminate the empty field and achieve the purpose of controlling and managing the ground pressure in the whole mine.
The tin mine south mine was once mined by the formal house and pillar mining method, and the volume of the empty area was increasing. Many of the goafs were not even processed in time, resulting in three large-scale ground pressure activities. In order to eliminate the damage caused by ground pressure in time, for the central and western empty areas where a large number of industrial plants, civil buildings and rivers need to be protected, the meteorite and tailings are used for filling, and the eastern part of the surface does not need protection. Some goafs at the edge of the area are forced to collapse with deep holes.
In order to fundamentally control the occurrence of mining site pressure activities, our company and the Changsha Mine Research Institute and other units have carried out new mining method research, and gradually adopt cementation filling mining method mining, which greatly reduces the loss of ore loss and maintains the stope. The safety of the roof.
Fourth, the roof of the stope monitoring
The use of the room-column mining method or the cement-filling mining method is a post-filling goaf treatment, and the exposure period of the empty roof is long. The monitoring of the roof of the stope is of great significance for the mining of the stope and the safety of the empty area.
The roof monitoring method of the stope can be divided into two categories: artificial macro survey analysis and instrument micro test and forecast. According to the work place, there are on-site monitoring and remote remote control.
(1) Manual monitoring.
The main task of manual monitoring is to go to the underground site to do macro surveys, statistical analogy analysis, mainly through artificial rock deformation, volume cracking, yellow mud, wood, rock sound and so on to achieve forecasting.
(two) instrument testing
It is tested by dozens of test instruments and research equipments of light, electricity, sound and machine. The instruments used for roof monitoring and testing are spring settler, ceiling pressure gauge, rubber mat, crack gauge, and top observer. Delaminator, top dynamometer, top plate pressure gauge, geophone, pole gauge, level, theodolite, etc.
The test content includes the settlement, translation, pressure, magnetoelectric potential, high frequency, etc. of the roof; the pressure condition of the column, the change of stress, and the surrounding roadway, especially the roof rock of the roadway.
The arrangement of the observation network is generally arranged along the direction of the ore layer, and the short axis is arranged perpendicular to the main axis every 50m-150m. The measuring point of the roadway should be placed in the axial part of the roof and the middle of the two walls. The measuring point of the pillar should be arranged in the lateral middle and 0.5m~0.8m away from the roof of the stope. The top point of the stop is generally fixed or laid at the end of the pole. The base point must be placed in a place where the bedrock is stable and accessible.
(3) Safety forecast
The post-harvest roof plate will produce bending deformation under the pressure of the covered rock layer. The amount of subsidence is related to the rock nature, the geometry of the stope, the boundary condition and the length of the empty roof. The amount of subsidence is small at the beginning of mining and then gradually increases. When the sinking amount of the top plate is W=150-170mm, the sinking speed is V≥1.5-5mm/day, and the sinking curvature is K≥2×10ˉ, the top plate of the empty area is in a critical state before the falling.
During the process of direct deformation and failure of the roof, the overburden on the roof also exhibits less deformation (sinking and dislocation), and its amount increases with time. The farther from the direct roof, the smaller the subsidence. At the same time as the top plate is separated from the layer, it is often accompanied by horizontal displacement. The height of the separation zone is generally equal to 2 to 3 times of the height.
V. Conclusion
The roof management of the stope is an important part of mine production. Our company has generally paid attention to it and spent a lot of effort to explore. A set of management methods for the roof of the stope has been basically formed, which has changed the passive state of the natural support roof by simply using rock stability. Actively using artificial support, actively carrying out the prediction and prediction of the roof, and filling the empty area in time after mining. The deformation of the surrounding rock of the roof is effectively controlled to prevent it from collapsing, which greatly improves the safe production conditions of mining, reduces the depletion of ore loss, improves the mining intensity, and contributes to the regular mining of the mine and the improvement of economic benefits.
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