Filling mining method

    I. Overview

The filling mining method fills the mining space with filling materials while returning the ore, and realizes the pressure control of the mining site. Regarding the mechanical effects of filling and controlling the ground pressure, although the viewpoints are different, the mass production practice proves that it can be summarized as follows:

(1) The filling body cannot change the stress distribution state of the excavated ore body and surrounding rock. After the excavation of the ore body, the stress balance of the original rock mass is destroyed, and the stress rise zone and the stress reduction zone are generated. The filling work always lags behind the recovery for a period of time, and displacement and deformation have occurred around the excavated ore body during filling. After filling, due to the small rigidity of the filling body, the active pressure can not be generated for the surrounding rock, and not only the original rock stress field can be restored, but also the surrounding rock continues to have a certain displacement and deformation.

(2) The filling body limits the displacement and deformation of the surrounding rock, reduces the damage of surrounding rock movement and reduces the degree of surface subsidence. This effect of the filling body is determined by the filling material, the filling method and the mining process. SMD (MDGSalaman) statistics show that some mines in Europe use different filling methods, and the roof subsidence coefficient is listed in Table 1. It can be seen from the table that the sedimentation coefficients of the roof vary greatly due to different filling methods. Mine of Jinchuan Nickel mine with two mining areas, Zhaoyuan Gold Mountain sub-ore, Xiangxi gold, tin, antimony ore mine filling mining method using different programs, backfill and surrounding rock surface displacement and deformation, have played good Control role.

Table 1 Roof settlement coefficient of different roof management methods

(3) The filling body applies lateral pressure to the pillar, so that the pillar is changed from the one-way two-way force state to the three-direction force state, thereby improving the strength of the pillar.

(4) After the recovery space is filled, the elastic strain energy release rate accumulated in the surrounding rock is reduced, thereby improving the ability of the underground structure to resist the dynamic load.

    2. The relationship between the confining pressure exerted by the filling body on the pillar (surrounding rock) and the properties of the filling material

The magnitude of the quartet pressure applied by the filling body depends on the deformation conditions of the pillar (surrounding rock) and the mechanical properties of the filling material used. Figure 1 shows the stress-strain curves of the pillars in GEBlight and IEClarke quartz cores for filling materials in rigid and soft-filled materials. It can be seen from the curve that the rigid filling can not only restrain the lateral deformation of the core, but also provide a large confining pressure. Although the core compression deformation has reached 1.75% (1.4mm), it has not reached the core failure strength limit. Core Strength Core quartz specimen strength with no confining pressure of soft filling material surrounded by almost the same, but it does provide some of the core damage resistance, constrains lateral deformation of the core so that the core has Large residual strength, the latter reaching 85% of the breaking strength.

Fig.1 Stress-strain curve of core with and without filling

1-unconfined pressure; 2 in soft filling materials; 3 in rigid filling materials;

4-level stress in soft filling materials; 5 - horizontal stress in rigid filling materials

Brett believes that the lateral restraint Δσ _h applied to the pillar by the filling body is:

In the formula:

σ _v - the vertical stress acting on the pillar surrounded by the filler, MPa;

Λ-lateral pressure coefficient, λ=1+sinø/1-sinø;

ø-Ore internal friction angle, (°)

Due to the lateral binding force exerted by the filling body, the pillar strength increase value ΔS _p can be calculated as follows:

ΔS _p =λΔσ _h ,MPa

The numerical simulation results show that the lateral displacement of the pillar after the filling of the goaf is significantly reduced. For example, when the mine is not filled, the lateral displacement is 41.9mm, and after filling, it is 18mm, which is 57% lower.

According to the simulation study made by similar materials in the laboratory, the filling method and filling height have great influence on the strength of the pillar. The test results are listed in Table 2.

Table 2 Effect of filling method and filling height on bearing capacity of pillar

It can be seen from the table that cementation filling has a greater effect on improving the support capacity (strength) of the pillar. Although the degree of filling is 85%, the strength of the pillar is increased by 25% to 27%. The vertical displacement of the Jinchuan nickel mine with different lime-sand ratios (1:4 and 1:8) as artificial column simulations (Fig. 2) shows that only the high-strength filling body can effectively control the roof. Shen.

Fig. 2 Comparison of the amount of roof subsidence after the first layer of mining after the two kinds of filling bodies are used as artificial pillars

1-Gray sand ratio 1:8; 2-Gray sand ratio 1:4

    Third, the interaction between the filling body and the surrounding rock

The vertical splitting (wall) filling mining method is taken as an example to illustrate the interaction between the filling body and the surrounding rock. Elastic foundation beam theory, research in this mining method slate top layer stress distribution and mechanical properties of filling materials relationship, determines the role of the filling body.

When using the elastic foundation beam theory to analyze the pressure acting on the roof rock, the following assumptions were made.

(1) As the mining work advances forward, the filled area is immediately filled with filling material.

(2) There are no pillars left in the mining area.

(3) The ore and the filling body are all elastomers.

(4) The load acting on the roof rock layer is evenly distributed, and the base value is q _o = γH.

Based on the above assumptions, the roof rock formation can be considered to be a beam that is placed on an elastic foundation. The working space between the backfill and the mining face is negligible. The computational mechanics model is shown in Figure 3.

Fig. 3 Computational mechanical model of stress distribution in roof rock stratum

1- ore body; 2-filler

On the x>0 side, ie the side of the ore body, the roof stress P _y ^o is:

In the formula:

K-ore resistance coefficient, Pa;

C-filler resistance coefficient, Pa;

El-modulus elastic modulus, Pa;

J-beam to neutral axis moment of inertia, m ⁴ .

It can be seen from the above formula that the stress in the roof rock layer is wavy, at x=0; P _y ^o has the maximum value, namely:

When x=∞, P _y ^o =q _o =γH

On the side of x<0, on the side of the filling body, the top plate stress P _y ^F is:

The symbol in the formula is the same as before.

As seen from the above equation, when x = 0, P _y ^F is the smallest, and its value is 0; when x = ,, P _y ^F = q _o = γH.

Comparing the above two formulas, at x=0, the stress P _y ^o acting on the working surface is not equal to the stress P _y ^F above the filling body, and P _y ^{o is the} largest, and P _y ^{F is the} smallest, that is, the stress jumps here. Change (Figure 4).

Figure 4 Stress changes in the roof rock formation

In addition, if the filling work is not timely, that is, C=0, the stress P _y ^o acting on the roof rock layer above the working surface will tend to infinity. At this point, the work surface must be destroyed and mining work cannot be carried out.

According to the application of numerical simulation calculation and analysis of the vertical stress in the filling body under different conditions, it is concluded that the vertical stress can reach the original rock stress value of 35% to 100% in the cemented filling of the gently inclined thin ore body. In the thick ore body, the vertical stress in the filling body is only 25% of the vertical stress value of the original rock. The results of stress measurements on the filling body from Singer's mine in Canada also show that the stress at the thinnest part of the ore body is high, and the pressure of the central part of the ore body is 0.6-0.65 MPa, while the edge is the thinnest. The location is 1.5MPa.

The tin mine antimony ore is filled with tailings and filled with mineral deposits to fill the ore column, and the ore body in the lower part of the river bed is smoothly extracted. The gob area is filled with tailings, which effectively controls the re-occurrence of large-area ground pressure. The Xiangxi gold deposit is filled with wall-cutting. The law returns to the gently inclined very thin ore body, which limits the movement and collapse of the surface due to the action of the filling body, and protects the surface buildings and rivers. These examples illustrate the mechanical effects of filling on improving rock mass stability.