Summary of treatment of goaf in caving surrounding rock

The essence of the empty area of ​​the collapsed surrounding rock is to fill the empty area with the collapsed surrounding rock or form a cushioning rock cushion to control the mine pressure, transfer or ease the stress concentration, and prevent the sudden collapse of large areas of the surrounding rock to generate air waves to the production area. Equipment and personal hazards.

Compared with the filling empty area, the method is simple and easy, and the cost is generally low. If it can be processed in time and reach the required range and thickness, it can ensure the safety of the production area and alleviate the stress concentration.

The caving surrounding rock treatment empty area is widely used in production and is generally applicable to:

1. The surface is allowed to collapse. If the surface needs protection, the ore body is buried deep, and the ore body overburden will not be displaced as a whole, ensuring that the rock movement will not develop to the surface after the collapse;

2. Back to the mining column and the treatment empty space are often carried out at the same time. If the ore is depleted and the loss is large, it should be used for the ore body with low ore value and grade; the surrounding rock ore is beneficial to the use of this method;

3, used for a variety of stable surrounding rock, but when forced to collapse the surrounding rock, its stability should ensure the stability of the ceiling project and operational safety.

The method of caving the surrounding rock is forced collapse, natural avalanche or a combination of the two

    1. Forced caving surrounding rock treatment empty area

When the surrounding rock is stable, the integrity is good, and it cannot fall naturally, the surrounding rock is forced to collapse by blasting. Compared with the natural caving, it is necessary to spend more on the treatment, but the range, quantity and timing of the collapsed surrounding rock can be controlled, and it is easy to meet the empty area treatment. Requirements.

There are several cases of forced collapse of surrounding rock:

(1) The empty area is close to the surface, and the forced collapse of the overburden makes the empty area communicate with the surface. The collapse of the surface table is beneficial to reduce the amount of treatment in the lower empty area, greatly alleviating and even eliminating the stress concentration of the lower ore body;

(2) The empty area is far from the surface, and the forced collapse of the surrounding rock fills the empty area. This method is beneficial to reduce the supporting pressure of the adjacent stope, but it requires a large amount of processing work;

(3) Forced topping at partial or interval to form a cushion or isolation belt to protect the working area. According to the stability of the rock and the timely, safe, favorable pressure control, as much as possible in the open field to reduce the loss and depletion of the pillar to determine the timing of forced collapse of the surrounding rock:

1. The isolated blind space without the pillars and the mines can be collapsed after the mining is completed;

2. An empty area with a column and no top column (the first stage of the steeply inclined ore body, the gently inclined ore body, and the large isolated ore body formed by the isolated blind ore body), under the condition that the ore rock is stable and allowed First, recover some of the pillars and then collapse the surrounding rocks;

3. When there is a column and a top column and the stability of the ore is not enough, the collapsed column and the collapsed surrounding rock are simultaneously carried out, but the column is detonated in advance.

If the empty area formed by the steeply inclined ore body is mined, if there is no significant hidden danger due to the elimination of the upper empty area, the local forced collapsed surrounding rock is generally used to form a rock pad with sufficient thickness to process the empty area. The measures of caving surrounding rock should be carefully studied to ensure the quality of the first collapse of the surrounding rock (first stage) and to form the required cushion thickness. If the cushion is thinner, the upper empty area cannot be collapsed naturally, and the forced topping should be added to ensure the thickness of the cushion.

The reasonable thickness of the cushion is an urgent problem to be solved. Generally, it is not less than 20~30m in production practice. The thickness of the cushion required under different conditions should be different. The speed of the airflow from the limit and the impact resistance of the bottom column are improved. Starting from the ability, the thickness of the cushion and the height of the empty zone, the scale and characteristics of the fall, the area of ​​the empty zone and the air escape tunnel, the rock mass of the cushion, the degree of compaction, and the strength of the pillar are related. The thickness of the cushion should be adjusted according to the actual experience of the relevant mines.

When the dip angle of the ore body is slow, the cushion layer will be partially retained on the bottom plate, and the cushion should be partially collapsed to fill the roof surrounding rock.

The following factors should be considered in determining the thickness of the avalanche roof in the ore body below the horizontal and moderately inclined intermediate thickness:

(1) Fully releasing the roof in time, so that the collapsed rock fills the empty area to reduce the supporting pressure of the adjacent working area;

(2) If the height of the collapsed rock cannot be guaranteed to be topped, at least the separation of the empty area and the working area shall be ensured to prevent the impact of the air wave;

(3) On the basis of the above, the amount of collapsed surrounding rock works should be minimized. Under suitable conditions, spacers can be used to form the isolation zone and induce the other roofs to collapse naturally.

The dense empty areas formed by the steeply inclined thin veins are mined, and the deep hole forced collapse cavities are used for the treatment (Fig. 1). The vacant areas in the upper 3~4 stages of the steeply inclined thin veins in China are generally formed by the mining method after mining, and the blasting works are not large with deep hole blasting. The empty area and controlled rock can be processed quickly. Move to create safe conditions for lower mining. In order to ensure construction safety, the distribution of empty areas should be investigated in detail, including: wall and its thickness; spatial distribution of pillars and their supporting role; weak surface state of geological structure; nature and stability of surrounding rock; And ground pressure activities. On this basis, the range and treatment plan of the wall collapse are reasonably determined.

Figure 1 Forced caving wall treatment empty area

1-gun hole; 2-clamped wall; 3-mining area

When the surrounding rock is forced to collapse, the size of the resistance line affects the layout of the treatment project and the cost of the explosion. The larger block size of the collapsed rock is beneficial to reduce the loss and depletion of the pillar recovery. Therefore, the minimum resistance line should be increased as much as possible to meet the requirements of empty area processing.

The collapse of the surrounding rock is smaller than the unit explosive used for the returning ore, and the resistance line is large. Generally, it is drilled with YQ-100 type and YZ-90 type deep hole rock drill. The hole depth is 10~35m, the hole diameter is 70~110mm, and the minimum resistance line is 3.5~6.0m.

When using the chamber to blast the empty area, the following factors affect the location of the drug room:

(1) The shape, location and exposed area of ​​the empty area;

(2) Processing the engineering quantity and its requirements;

(3) The size of the minimum resistance line and the stability of the surrounding rock in the empty area;

(4) Facilitate the construction of the drug room roadway and ensure the safety of construction.

The safe distance from the entrance of the drug room to the edge of the empty area changes with the inclination of the ore body, and the distance of the large inclination is small. To this end, we should understand the exact shape and surrounding position of the empty area to ensure the safety of the construction of the drug room roadway. The layout of the drug room roadway is simple, and the level of the drug room is small, which can reduce the workload of the drug room and improve the filling efficiency of the charge and the roadway. After the charging, the drug room roadway is filled with waste rock or blasted in the roadway, and the latter method is simple, high efficiency and good working condition. The packing length is generally 6-8 m.

    Second, natural caving surrounding rock processing empty area

The planned collapse of the mining column to expand the exposed area of ​​the empty area (or local forced collapse of the surrounding rock at the appropriate location) induces a natural collapse of the roof of the empty area.

The first stage of mining inclined, gently inclined ore body, or steeply inclined thick ore body, when the blasting property of the empty area roof is better, it is beneficial to treat the empty area with natural caving surrounding rock. When mining other stages of steeply inclined thick ore bodies, depending on the stability of the surrounding rock, the ore pillars, or a group of ore pillars, may be recovered in sequence, under the protection of the ore cushion or by the collapse of the rock. The upper (lower) disk surrounding rock naturally collapsed.

Mastering the natural caving law of the roof is a prerequisite for the smooth use of natural caving to treat empty areas. Each layer of roof should understand the nature of the distribution of geological weak plane of the top plate allowing area and time exposure, development and caving height, with the corresponding measures inducing caving. Ideally, the roof should be able to collapse naturally and gradually to the required height in a timely and gradual manner. In order to isolate the topping area from the working area, if necessary, leave a temporary pillar or a partially forced collapse roof to form an isolated rock belt. Closed measures should be strengthened in areas with high altitudes.

Compared with the forced caving method, the natural caving treatment empty area has the advantages of simple process and low processing cost, and can be used under suitable conditions to replace the forced collapse surrounding rock treatment empty area. In the Dongshan inhabited mountainous area in China, in the treatment of the empty area formed by the mining method in the staged rock drilling stage, a method of planning the return of the mining column to enlarge the exposed area of ​​the empty area to induce the natural collapse of the surrounding rock was adopted. The ore body has a dip angle of 50-70° and a thickness of 6-18 m. The upper plate is silicified dolomite , which is relatively stable. The lower plate is purple slate which is moderately stable. Generally, after mining 1 or 2 mines, the mining column and the top and bottom pillars are released, and after the ore ore is released for 2 to 3 months, the surrounding rock of the roof can be naturally collapsed to fill the empty area.

The disadvantage of natural caving surrounding rock treatment empty area is that the law of natural collapse of the roof is difficult to master, and the process and scope of the caving are difficult to control. If there is not enough rock cushion and strict sealing measures in the upper part, it will pose a threat to the safety of the production area.