Study on the state of collapse and the movement law of internal ore
The sublevel caving method without bottom pillar has the advantages of high work efficiency, good safety, high production intensity and low cost. It has been widely used in China's underground iron mines [1-2], and currently accounts for underground mines. About 80% of the total output. Since the blasting and production of the mining method are carried out under the cover of loose rock formation, the loss rate and the depletion rate have always been serious problems faced by the method [3]. To this end, domestic and foreign experts and scholars have carried out a lot of research and experiments on the movement law of loose ore, the optimization design of blasting parameters and the management of mining. However, the one-sided effect of the research object is not ideal.
Zhang Guojian et al [4-5] proposed the concept of caving body. The study found that the decisive role of the caving body in the production system and the internal rock movement law have important practical significance.
1 collapse body
The caving body is the ore explosion pile formed in the loosely covered rock layer under the action of blasting [4-5], which is not only the loose ore body formed by the blasting, but also the object of the ore mining work. Therefore, the collapse body is at the center of the blasting work and production and release. The change of the blasting parameters will inevitably affect the shape and internal state of the caving body, and the different caving body states correspond to different ore-concentrating effects. Blasting, ore-mining, re-blasting, and re-mineralization are a cyclical work of mining production. Therefore, the former one-step ore-mining will affect the formation of the collapse body in the next step. If the collapsed body is not in good condition, a bad cycle will be formed. State, and good collapse body state will always maintain good production technical indicators.
Since the blasting and ore-extraction of the method are carried out under the cover rock, it is difficult to accurately observe the shape of the collapse body and the internal rock movement law at the production site. With the development of computer technology and numerical calculation methods, numerical simulation technology has become the main means of this research direction. In the research, the particle flow program PFC2D is used to simulate the state of the collapse body and the movement law of the internal ore particles during the ore-extraction process.
2 simulation method
The PFC2D two-dimensional particle flow program is a discrete element software developed by Itasca, which simulates the motion of circular granular media and the interaction between particles. It is used as a simulation software for studying the properties of granular media in landslides, mining, blasting, etc. Many fields have been widely used [6]. The particle flow method adopts the explicit time-step center finite difference cycle algorithm. The medium is assumed to be a discrete body, and the equilibrium equation needs to be satisfied between the particles without satisfying the deformation coordination equation, which is obviously different from the continuum mechanics problem. If the resultant force and resultant moment acting on the particles are not equal to zero, the particle motion law is determined according to Newton's second law. The movement of the particles is not free and is limited by the resistance of the surrounding particles. The most basic characteristics of the particle flow are: allowing the particles to have a finite displacement, and the rotating particles can be completely detached; the particle flow can automatically identify new contacts during the calculation process.
3 caving body shape and ore movement law
3.1 Model establishment
In order to simulate the appearance of the cavities under blasting and the stress distribution characteristics of the caving in the pre-mineralization, the numerical simulation test was carried out with reference to the actual mine parameters. The test parameters are set as follows:
The section height is 12m, the height of the collapse is 18m, the thickness of the covered rock is 24m, the height of the ore approach is 3m, the step of the collapse is 2m, and the ore particle size of the model is 10~15cm. A total of 1140 ore particles are formed, covering the rock block 20 ~30cm, generating 7,300 top and front cover rock particles. The mechanical parameters of the model ore rock particles are shown in Table 1.
3.2 Cavity form
The simulation of the collapse shape in the study is divided into three steps: 1 to carry out the initial stress balance of the overburden, the initial stress balance state as the boundary condition of the ore blasting; 2 to increase the ore particle radius to simulate the ore blasting, and the blasted ore forms a surrounding rock formation. Extrusion; 3 By changing the radius of the ore, the ore particle radius is changed back to the initial state, the retraction effect after the blasting is simulated, and the new stress balance state before the ore deposit is formed by covering the rock formation and the caving ore. The collapse body is formed by the above three steps, and the form before the ore is as shown in FIG.
The simulation results show that the shape of the collapse is similar to that of the ellipsoid, the width of the collapse is larger than the step of the collapse, the width is about 1.3 times of the step of the collapse, and the height of the collapse is greater than the height of the collapse, but the increase is not obvious. It can be seen that the expansion direction of the blasting action is along the horizontal direction of the mining approach, and the vertical expansion is not obvious. The boundary of the caving body is not smooth and is obviously jagged, indicating that there is a mixture of minerals and rocks in the outermost layer of the caving body, which is caused by the expansion and retraction of the blasting.
3.3 Analysis of the movement law of ore rock in the caving
In order to study the evolution of the caving body during the ore-mining process and the internal rock movement law, the ore-forming work was carried out regularly on the basis of the formation of the collapse body state, and the ore movement of the caving body and the surrounding overburden layer was carried out simultaneously. Monitoring, monitoring program shown in Figure 1.
In the numerical model, four calibration layers are uniformly set, and each marker layer is provided with monitoring particles. The monitoring indicators mainly include x-direction displacement and y-direction displacement. Through these indicators, the motion law of particles during the ore-boring process is studied. According to the needs of the research, four layers of monitoring points are set in the model, and the monitoring points are evenly arranged in each monitoring layer, a total of 23 points. The first layer monitoring point number is 1#～5# from left to right, the second layer monitoring point number is 6#～11# from left to right, and the third layer monitoring point number is from left to right 12#～17 #, The fourth layer monitoring point number is from left to right as 18#~23#. The relationship between the displacement of 1# measuring point and 6# measuring point and the time of ore discharging in the process of ore mining is shown in Fig. 2.
During the process of ore-mining, the movement law of ore particles within the caving body:
(1) The movement law of ore particles in the middle of the collapse body is as follows: during the movement of the ore from top to bottom, the horizontal movement of the ore particles at the initial points is not obvious, and the vertical movement is relatively stable, but the displacement of the vertical movement is dependent on the distance. The distance between the blasting end walls is reduced and the horizontal movement is gradually increased, and the fluidity is enhanced, which is caused by the gradual approach to the ore discharge port.
(2) The ore particles in the contact between the cover layer and the top of the collapse body are mainly vertical movement, and the ore near the blasting end wall has no horizontal displacement. As the distance from the end wall increases, the horizontal movement tends to be obvious, and the collapse body and The interface covering the rock formation moves toward the blasting end wall, causing the width of the caving body to gradually narrow.
4 Conclusion
(1) Numerical simulation of the formation of cavities, experienced three stages of initial stress balance, expansion extrusion and post-explosion retraction, the enlargement and reduction of ore particles, reflecting the true formation state of the caving body, the caving body The state is approximately ellipsoid, the upper width is narrower, and the dominant direction of blasting expansion is horizontal.
(2) During the process of ore-extracting, the vertical movement velocity of the particles in the lower part of the caving body is first and then small, while the horizontal movement speed is small and then large; the ore particles near the blasting end wall in the middle of the caving body are mainly vertical movement, and the horizontal movement is not obvious; The particles moving away from the end wall are more and more obvious with the horizontal movement of the ore; the movement law of the top particles is similar to that of the middle particles, but the horizontal movement appears to be more lagging.
references
[1] Chen Qingyun, He Yuzao. Optimization of structural parameters of sub-pillar collapse method in small and medium-sized mines [J]. Metal mines, 2005 (1): 23-25.
[2] An Hong, Hu Xingbao. Application status of sublevel caving without pillars [J]. Mining Express, 2005 (9): 6-8.
[3] Zhang Zhigui, Liu Xingguo, Yu Guoli. Bottom-free sublevel caving method without depleted ore-extraction theory and its practice in mines [M]. Shenyang: Northeastern University Press, 2007.
[4] Zhang Guojian, Cai Meifeng. Study on the shape and impact of caving body [J]. China Mining, 2003 (12): 38-42.
[5] Zhang Guojian, Yan Huichao. Study on the relationship between the release body, the loose body and the collapse body without sub-column sublevel caving method [J]. China Mining, 2010 (3): 68-71.
[6] Zhou Jian, Chi Yong, Chi Yuwei, et al. Particle flow method and PFC2D program [J]. Rock and Soil Mechanics, 2000(3): 271-274.
Article source: "Modern Mining"; 2016.9;
Author: High victorious; Anshan Iron and Steel Mining Group Company Gongchangling mine;
Wen Yanliang ; School of Mining Engineering , Liaoning University of Science and Technology;
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