The caving mining method is a mining method that collapses surrounding rock during mining to achieve ground pressure management and mineral resource recovery, in which the surrounding rock is collapsed by natural caving surrounding rock and planned forced collapse of surrounding rock.
When adopting this mining method, the ore body no longer divides the mine room and the pillar, but adopts single-step recovery. The biggest feature is high production efficiency, safe operation and flexible use, but the basic premise of its use is that the surface allows collapse. Development of China's mining industry started late, most of the 1970s designed to use mine caving mining method to mine the metal, for example, ferrous metal mining caving mining in a mining accounts for over 85% of the amount of ore, non-ferrous mines accounted for 30 %about. Mines using the caving mining method in the world account for about 25%.
According to the vertical height of the mining face, the caving mining method can be divided into a single-layer caving mining method, a stratified caving mining method, a sub-level caving mining method, a stage forced caving mining method and a stage natural caving mining method. The advantages and disadvantages of various methods are different. The single-layer caving method and the stratified caving method generally adopt shallow-hole rock drilling and ore mining. When the ore body is mining, it is necessary to support the working space, and with the advancement of the mining working face, the caving is carried out. Covering the rock filling area, the two mining methods have complex processes and low production capacity, but the ore loss is small. The sublevel caving and stage forced caving mining method generally adopts medium and deep hole rock drilling and ore mining, and its production capacity is large, but the ore loss and depletion are also large. In the stage, the natural caving method needs to utilize the incompleteness of the ore body itself, and after the formation of a large bottoming space, the ore body is realized by the weight of the ore body. The methods currently used in metal mines at home and abroad are the sub-column sublevel caving mining method and the stage natural caving mining method. The two caving methods have strong typicality in China.
Stage 1 natural caving mining method
1.1 Application Status
In the stage of natural caving mining method, after the bottom space is formed in the lower part of the ore block, the ore loses the lower support. Under the combined action of gravity and ground pressure, the crack first occurs in the middle of the nugget and destroys, and then gradually collapses naturally [1] . The stage natural caving method is favored in suitable conditions for its large production capacity, high labor productivity, low mining cost and high safety. Currently, it is 50 in more than 20 countries including the United States, Canada, Chile, Indonesia, South Africa and the Philippines. It has been applied in several mines [2]. Its mining model is shown in Figure 1.
At the stage of the natural caving method, with the advancement of the mining face, the ore body is covered by the planned overburden rock, and the mined area is filled with the ore body to achieve the management and control of the ground pressure. The basic feature is that it collapses the surrounding rock and recovers part of the mine pillars. It is suitable for ore bodies where the surrounding rock is easy to collapse and the surface is allowed to collapse. In the natural caving mining method, as the ore body gradually collapses, a pressure balance arch is formed on the roof of the caving ore [3], and the upper ore body is difficult to collapse. For this purpose, the ore body caving process and boundary are required to be artificially controlled. The ore body in the block continues to settle stably and does not exceed the design collapse range. Commonly used to break the balance arch is to move the A and B points of the arch support along the vertical direction. The boundary control method is to drill deep holes at the boundary of the ore block to weaken the boundary of the collapsed ore body. The development of pressure balance arch is shown in Figure 2, and the boundary control of the nugget is shown in Figure 3.
Technical development of China's mining started late last century, introduced from abroad this kind of mining method, initially a mining method [4] Yimen copper mine in Sierra Leone iron ore pit and Laiwu mazhuang, after Jinshandian iron ore, Jinchuan The mines such as nickel ore, Chengchao iron ore, Jingtieshan iron ore, copper ore, copper deposit, Fengshan copper mine, Sichuan Shimian mine and Handan iron ore have been tested. The production capacity of copper ore and copper mine is 4 million. t/a [5]. See Table 1 for some of the mine production technical indicators using the stage natural caving mining method.
The stage natural caving mining method is widely used in foreign countries. The mining of only a few mines such as copper ore and copper mines in China's metal mines has been successfully tested. Other mines have failed due to various reasons such as structural parameters, stope control and mine management.
1.2 problems
When adopting the stage natural caving mining method, although the mining process is greatly simplified, the management is convenient, the efficiency is high, there is no need to blast and mine, and the cost is low, but the engineering practice shows that the natural caving mining method has high risk, and there are still many technical problems in its industrial application. Mainly in the following five aspects:
(1) The geological data is not accurate. The evaluation of the collapsibility and mining design of the natural caving mining method at the stage needs to be based on accurate geological data. The accuracy of the geological data plays a crucial role in the implementation of the method.
(2) The continuous collapse of the ore body. Although the application premise is the destruction of ore body and the development of joint fissures, engineering practice has proved that if the quality of the induced collapse is poor, it will lead to the continuous collapse of the ore body and affect the mine production.
(3) The ore body blockiness is difficult to control. Since most of the ore bodies are self-heavy and partially artificially induced, the ore body collapse is difficult to control, and the large block processing is difficult and the safety is poor, which directly affects the mining efficiency.
(4) The mining management is complicated. Most of the mine discharge deadlines rely on the experience of field personnel, no system theory guidance, difficult grade management, ore loss and depletion control is difficult.
(5) The bottom structure is difficult to maintain. Due to the large scale of the ore body collapse, the transient pressure of the balance arch is obvious, which affects the stability of the bottom structure and is difficult to maintain in the later stage.
1.3 Development trend
(1) Quantitative study on the collapsibility of ore bodies based on geological data input. Establish a research model of ore body collapsibility based on geological data input, and conduct quantitative evaluation of ore body collapsibility through quantitative data control to provide more accurate basic data for mining design.
(2) The height of the stage is improved. Due to the large amount of work and long time for the mining of the natural caving mining method, in order to make full use of the mining project and improve the production efficiency, it is necessary to further study the height of the increasing phase, which is increased from about 100 m to 300-400 m.
(3) Application of large-scale equipment without rails. Simplify the bottom structure and make full use of the capacity advantages of this mining method by using large-scale equipment without rails.
(4) Prediction of caving ore blockiness. According to the development of the joints of the ore body, the ore collapse prediction is predicted.
(5) Globalized quantitative ore mining management. The ore-mining management is a crucial step in the caving method. The ore-mining technology research combining the similar simulation of the ore-mining and the computer simulation is carried out. According to the law of the movement of the ore, the comprehensive mining management method of the caving method is proposed.
2 pillarless sublevel caving mining method
2.1 Application Status
The sublevel caving mining method without bottom pillar is to use plane unfolding and stratification, cutting the ore body in the way, and drilling the medium and deep hole. The mechanization in the way is a kind of mechanization is relatively high, the operation is relatively safe, and the mining cost is low. Mining method. This method was introduced from Sweden to China in the 1960s [6]. It is currently the most efficient mining method for iron ore in China, and it is also used in chemical and non-ferrous industries. The mining model is shown in Figure 4.
The most important stope structure parameters of the pillarless sublevel caving mining method are the combination optimization between the route spacing, the section height and the collapse step [7]. In general, the section height is determined in the middle section. It is difficult to change after mining, and the adjustment of the approach spacing and the collapse step is relatively flexible. Secondly, the factors affecting the mining method are rock drilling and mining equipment.
When this method was first introduced in China, the segment height and the approach spacing were basically 10m×10m and 8m×8m[8], and this structural parameter has been used for a long time due to the limitation of equipment application. The earliest mine in China to apply this method is Xiangshan Pyrite , which uses low-segmentation, its height is only 4.5m, and its production efficiency is low. After the 1990s, several large mines in China introduced large-scale rock drilling equipment, and then conducted large-scale tests. For example, the Huashugou iron ore mine increased the section height and the approach spacing to 20m. The Meishan Iron Mine was launched. The tests of 15m×15m and 20m×20m spacing have improved mining efficiency to different extents, reducing the cutting ratio and mining cost. The mine production parameters of some of China's sub-column-free sublevel caving mining methods are shown in Table 2.
2.1.1 Large spacing and high segmentation
According to recent mining studies and field practice applications, when the approach spacing and the segment height are equal, it is not the best combination. It is necessary to determine the parameters of the ellipsoid at the five-point tangency according to the plane of the ore ellipsoid. The combination is the generally high-segment and large-pitch structure [9-10] (Fig. 5, Fig. 6).
The large spacing is based on the fact that the ore ellipsoids of the two adjacent approaches of the segment are not tangent, but are tangent to the ore-electing ellipsoid in which the upper and lower segments are arranged in a diamond shape, and the ore-erating ellipsoid in the segment is in the flow. Tangent on the axis, forming a five-point tangency (Figure 5). The ratio of the segment height to the approach pitch is
Where H is the height of the segment, m; B is the path spacing, m; a is the long semi-axis of the ore ellipsoid, m; b is the short semi-axis of the ore ellipsoid, m.
The theoretical basis of the high segmentation is that the ore ellipsoids of the two adjacent approaches are tangent to each other and are tangent to the ore-electing ellipsoid in which the upper and lower segments are arranged in a diamond shape to form a five-point tangent (Fig. 6). The ratio of the segment height to the approach pitch is
Where H is the height of the segment, m; B is the path spacing, m; a is the long semi-axis of the ore ellipsoid, m; b is the short semi-axis of the ore ellipsoid, m.
Large spacing does not refer to large parameters, but rather that the approach spacing is greater than the segment height. The factors influencing the structural parameters of the stope are mainly the occurrence conditions of the ore body, the mining scale, the level of mining equipment, the explosiveness of the ore body, etc. It is necessary to integrate the various influencing factors to optimize the parameters.
2.1.2 Low depleted ore deposit
In recent years, the research and experiment on low-depleted ore-concentrating has been carried out, that is, several layers are used as the assessment unit for ore recovery. When the upper part of the layer is recovered, the ore that has collapsed in each step does not need to be completely released but is appropriately left. In order to reduce the degree of mineral rock mixing at each subsequent step, the high-grade mined ore is obtained [11]. Some mine production indicators in 2010 are shown in Table 3.
Maintaining the basic integrity of the ore-rock interface is an important process requirement for controlling low-depleted ore deposits. In order to achieve low-depleted ore deposits, it is necessary to keep the rock-rock interface from generating large cracks from the analysis of the dynamic movement law of the ore. See Figure 7 for the downward movement of the rock interface under low-poor ore-mining conditions.
The main differences between low-depleted ore and cut-off grades:
(1) The stepping distance is no longer used as the mining management unit, but is considered in several layers and is comprehensive.
(2) Artificially remove the residual ore from the upper layer as the isolation layer to reduce the depletion.
(3) The rock mixing is well controlled.
(4) Multi-stratified management of the comprehensive domain makes the stope management simple. Low-depleted ore deposits can be used at the ore-rock interface within the controllable range, and only for the ore that is out of control and beyond the controlled rock interface (such as the interface between the rock and the rock on the lower plate and the boundary) Recycling opportunities should also use current cut-off grades to reduce ore losses.
Comparing results of cut-off grade ore and low-depleted ore deposits: in terms of ore recovery rate, the first three cut-off grades are higher than the low-depleted ore deposits, and the two types of ore-mining methods are the fourth. The ore recovery rate of the segment is close, and the ore recovery rate of the fifth section is basically the same. For the ore recovery rate below the fifth section, the low-depleted ore is slightly higher than the cut-off grade. This kind of ore-mining method is applied properly. Under the condition that the ore recovery rate is not reduced, the comprehensive depletion rate of ore can be reduced to 4% to 6%.
In addition, in terms of the impact of ore recovery rate, Wu Aixiang et al [10] through the combination of theoretical analysis and numerical simulation, once again proved the three major factors of the route spacing, segment height, and ore spacing for the ore recovery rate. The impact is different. Among them, the segment height has the greatest impact on the ore recovery rate, and the route spacing is second. The least affected is the ore-feeding step. This is consistent with the results of field practice.
2.2 Problems
Although the bottomless sublevel caving mining method has been greatly developed, there are still many problems in domestic mine applications:
(1) The equipment is too small. Small and medium-sized rock drilling equipment and mining equipment are generally adopted in China, which limits the increase of the structural parameters of the stope.
(2) The structural parameters are small. The small structural parameters lead to the dispersion of mining operations, low mining efficiency, and relatively high cutting, which restricts the production capacity of the sub-column sublevel caving mining method.
(3) Despite the use of low-depleted ore deposits, ore loss and depletion are still large. Compared with the empty field method and the filling mining method, the waste rock is widely mixed and difficult to manage, resulting in high ore depletion and affecting the quality of the ore produced. This is also the most prominent problem.
2.3 Development trend
(1) High-segment, large-pitch mining. With the development of the sublevel caving mining method without pillars, engineering practice has gradually proved that high segmentation and large spacing are the development trend, and it has been successfully tested abroad, which can reduce ore loss and depletion, and give full play to large mining equipment. Advantages, reduce the cutting ratio, and reduce mining costs.
(2) Large trackless equipment applications. The use of large-scale trackless mining equipment is an important guarantee for increasing the structural parameters of the stope, and is an important way to improve the production capacity and economic benefits of the sublevel caving mining method without bottom column.
(3) In-situ ore mining research. The existing ore-mining theory research is mostly based on similar material simulation, and its geometric similarity is easy to realize, but the similarity in the dispersion dynamics is difficult to simulate, and the simulation test data has certain limitations. Therefore, on-site in-situ ore mining research based on equipment detection systems is an important development direction.
3 Conclusion
The caving mining method has developed in China for several decades. Among them, the sub-column sublevel caving mining method has been applied in most iron mines and has been greatly developed. In recent years, along with the application of large-scale equipment, The development in high segmentation and large spacing has gradually become a trend. The stage natural caving mining method has fewer application cases for mining engineering due to its strict application conditions, but its advantages of huge quantitative production capacity and low mining cost make it suitable for use in applicable mines, and with the development of the geological database computer model, Its mining control is improved, and it is developing towards high-level and globalized quantitative ore management technologies. Although the caving method will form a collapse pit on the surface, with the gradual development of the technology of solidified tailings and waste rock backfilling collapse pits, the collapse control method and the reclamation technology after the caving method will make the caving method in cost control and underground. The advantages of pressure control appear. Therefore, the caving method will continue to play a role in cost reduction and synergy in metal mining for a long time to come, and the application potential is large.
references
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[4] Feng Xinglong. Digital evaluation and simulation technology of natural rock mass engineering rock quality [D]. Changsha: Central South University, 2010.
[5] Ming Jian, Shan Qiang, Yan Rongfu. Research on support technology of soft broken surrounding rock roadway in natural caving method [J]. Journal of Mining and Safety Engineering, 2014(1): 34-40.
[6] Guo Lei, Xiong Yuhui. Status and development trend of sublevel caving without pillars [J]. China Mining Engineering, 2010, 39(6): 44-48.
[7] Liu Jinshan. Study on process parameters of sublevel caving method without pillars in Shirengou Iron Mine [D]. Tangshan: Hebei Institute of Technology, 2009.
[8] Tao Ganqiang, Ren Qingyun, Luo Hui, et al. Stability analysis of stope without sublevel caving method [J]. Rock and Soil Mechanics, 2011, 12: 3768-3772, 3779.
[9] An Long, Xu Shuai, Li Yuanhui, et al. Optimization of caving method based on multi-method combination [J]. Journal of Rock Mechanics and Engineering, 2013(4): 754-759.
[10] Wu Aixiang, Wu Licong, Liu Xiaohui, et al. Study on structural parameters of sublevel caving without pillars [J]. Journal of Central South University: Natural Science Edition, 2012(5): 1845-1850.
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Article source: Modern Mining, 2016.12;
Author: Sun Kwok-kuen, Wang Xing, Yang Mian; Sinosteel Maanshan Institute of Mining Research Co., Ltd., State Key Laboratory of Metal Mine Safety and Health, Hua Wei metal mineral resource efficient recycling of National Engineering Research Center Co., Ltd.;
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