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How to form a rock cover by using a sublevel caving method without a bottom pillar
(1) The role of covering rock formations
When using the pillarless sublevel caving method to return to the ore body, a certain thickness of the overburden layer must be formed in the upper part of the pile. The effect of covering the rock layer is:
1 Use the overburden to form extrusion and fracture conditions to improve ore recovery and depletion indicators. Because there is no cover rock, the collapsed ore has collapsed into the empty area, and most of it cannot be released in this section.
2 Use the cover rock to form a safety cushion. If there is no cushion, once the surrounding rock collapses a lot, it will cause serious safety accidents, not only can not produce, but also directly threaten personal safety.
(2) Covering the thickness of the rock formation
The thickness of the overburden should be as small as possible to minimize the total amount of collapsed surrounding rock, and meet the requirements of the mining process and the safety at the time of operation. At present, the thickness of the cover rock commonly used in China is: not less than twice the layer height, but this thickness Whether it is reasonable or not, it still needs to be adjusted in the future practice and continuous summing up experience.
[References] Found temple iron ore is known from, overburden thickness, minimum 25 meters, a maximum of about 50 meters.
(3) Cover the blockiness of the rock formation.
The block size of the cover layer is required to be larger than that of the collapsed ore block. Otherwise, during the process of the ore release, the rock will pass through the gap of the ore and flow to the mining roadway, causing premature depletion.
Therefore, there are many YA-100 shallow hole drilling machines for deepening the surrounding rock. The minimum resistance line and the hole bottom distance of the blasthole take a large value (generally 4 to 5 meters), and the waste rock collapses into a large block to reduce the depletion.
(4) Method of forming a cover layer:
1) Method of forming a covered rock layer under ideal conditions
1 The upper part of the ore body has been recovered by other methods, and the empty area has been treated, and then it is replaced by the sub-column sublevel caving method. At this time, the covering rock layer has naturally formed.
(such as the Dumiao iron mine, the upper part is mined by the small middle section method, and the bottom is mined with the bottomless column)
2 The upper part is mined in the open air. When it is imported into underground mining, it can be used to form an open rock slope or a stripped waste rock to form a covered rock layer (such as the Banshigou iron ore).
3 The blind ore body with unstable surrounding rock, with the ore mining, the surrounding rock can naturally collapse to form a cover layer.
2) Forced to collapse the surrounding rock of the roof to form a method of covering the rock.
The above ideal conditions are not many. Most of the mines in China that use the sublevel caving method without pillars are from the first segment and are mined by the bottomless column method. This requires forced collapse of the roof surrounding rock to form a covered rock formation.
There are two ways to form a covered rock formation. One is to collapse the roof surrounding rock with the recovery, and the other is to collapse the roof surrounding rock in a large area (ie, to concentrate the top)
1 method for collapsing the roof with mining
In this method, the cutting channel is formed in the upper part of the first section and the cutting channel is formed in the same manner as the mining. As the lower mining work progresses, the upper top hole is gradually collapsed.
In this way, in the first section of the mining, a cover layer can be formed, and the ore can be collapsed under extrusion and blasting conditions, and the ore can be discharged normally.
There are many mines using this method.
2 large area caving and topping method (concentrated topping)
In this method, when the mining area forms a certain exposed area, a deep hole or a medium-deep hole is drilled in the rock drilling roadway or the patio on the side of the topping area. A large area collapsed the roof.
(Advantages) This method is simple in process, concentrated in topping work, easy to organize, and does not interfere with the topping work and the mining work, and the cutting work does not require cutting. There is also no need to release waste rock. The topping blasting conditions are good.
(Disadvantages) Most of the ore in the first segment collapses into the empty zone, that is, the first segment is carried out under uncovered conditions, and the safety of the mining work is poor. The ore loss is large, and the top blasthole is arranged on the surrounding rock of the large exposed area. If the surrounding rock is partially collapsed before the roof is released, it will be destroyed and the blasthole will be placed, so the reliability of the topping work is poor.
For the gently inclined ore body, when the surrounding rock cannot fall naturally, it is necessary to forcefully collapse the surrounding rock and continuously replenish the waste rock cover layer. It is a method of combining the forming cutting groove with the topping.
3 methods for forming a cover rock layer
In this method, after the first section is recovered, the formed goaf is used as the compensation space, and the upper surrounding rock is forced to form a cover layer. The advantage of this method is that the topping work is concentrated, the topping process is simple, and the structure is easy to organize. The topping work and the mining work do not interfere with the topping work and do not require cutting. The disadvantage is that the work reliability is poor.
4 Ways to collect the top of the rock to form a covered rock layer:
(A) This is intended to dig the top of the first section of the top of the roadway, in which the deep hole of the fan is aligned with the blasting hole of the blasting hole, and the cutting groove is formed like the mining. Taking the ore block as the topping unit, the top of the mining block will first collapse several rows of blastholes and install parts to loosen the upper ore and waste rock.
Advantages - safe and reliable work, ore damage,
Disadvantages - the topping process is complicated, and it is required to pick up the mining lanes in the mines at the same time, and keep them in a straight line, which is conducive to the topping work.
(B) A top lane is added to the top and the back. The topping and the recovery are combined into one side process, which does not need to dig a large number of top rocking roadsides in the upper surrounding rock, and only needs to be controlled in the upper surrounding rock and the corresponding cutting position into the top cutting groove, in the mining lane Drill the deep and medium holes of the same compartment in the side. Use the deep hole to control the block height and height of the mine with deepening control of the top height (up to 20 meters).
5 first put the top and then pick it up to form a cover layer:
This is to dig a layer of one or two layers of rock-filled roadway in the surrounding rock of the ore body before mining, and fan the blasthole in it, (W put W back ), and dig the cutting lane at the end A cutting groove is formed. The surrounding rock is collapsed by the caving ore method to form a covered rock formation.
Advantages - The first section of the mining is carried out under the overburden and there is a safe and reliable mine loss.
Disadvantages - the topping workload is large, and some of the seat stones are shipped.