Mine chute is the throat of mine transportation, and its operation directly affects mine production. During the process of mine discharge, the ore frequently collides with the slip wall and collides, resulting in damage to the well wall. This paper proposes a new type of shaft discharge structure, and studies the ore slip law through PFC3D, optimizes the unloading structure parameters, effectively reduces the impact of the ore flow on the upper slide structure, and prolongs the service life of the shaft.
1New type of shaft discharge structure
A multi-metal mine copper Mary Tibet Autonomous Region "95" focus on mineral exploration projects "fifth" period, copper and lead polymetallic ore belt by Kanayama, Copper Mountain are high 5042,5302.50m, and contrast The bottom of the Xiagong Pugou and the Brown Groove are only 4,500m, and the relative height difference is more than 540m. In order to solve the problem of high ore difference in ore transportation, an ore chute transport system is adopted. The transfer chute is divided into two parts, the upper elevation is 4484~4269m, the height is 215m, the lower elevation is 4261~4095m, and the height is 166m. The traditional shaft unloading structure is shown in Figure 1(a). The impact of the ore on the upper shaft wall is concentrated in 2~30m [1-2]. Due to the development of various rock mass structures in the engineering area, the thickness of the weathering belt is relatively large. Under the impact load of the ore, the upper structure of the chute is prone to damage and smashing, which seriously threatens the normal safe production of the chute.

To this end, this study fully considers the factor of reducing the impact dynamic load damage, and proposes a new type of shaft unloading structure (Fig. 1(b)). The bottom of the unloading pit adopts a flat bottom structure to form a dead ore pile, which reduces the impact and wear of the material on the unloading pit, and slows down the material speed; the small-diameter funnel, that is, the center falling ore funnel, concentrates the ore, reducing the initial velocity of the ore due to its unloading to the wellbore wall Direct impact damage, well protected the structure of the slippery well.
2 Optimization of unloading structure parameters of main chute
2.1 PFC3D numerical model of a new type of shaft discharge structure
PFC3D is a large-scale three-dimensional numerical program developed by ITASCA based on the discrete element method to simulate the motion and interaction of circular granular media [3]. In recent years, it has been used in the mining industry for its analytical blasting, caving mining and smashing systems. Etc. [4-5].

According to the original design data: the ore block is not more than 500mm, the natural angle of repose is 40°, the 10m3 fixed type mine car, the numerical model of the mine car and the ore is established, and the unloading station and the chute structure are used in the design to establish the runoff unloading model. See Figure 2.

2.2 PFC3D simulation results of a new type of shaft discharge structure
In order to analyze the influence of parameters such as the size and height of the blanking funnel of the center on the convergence effect of the ore flow, the same 10m3 fixed mine car and the unloading pit of the same size are used in this paper to compare the cross-sectional dimensions and funnel height of different center blanking funnels. The simulation.
2.2.1 Determination of the cross-sectional dimension parameters of the center blanking funnel
In order to determine the cross-sectional dimension of the center blanking funnel, the size of the cross-section of the center blanking funnel is 2m×2m, and the cross-sectional dimension of the center blanking funnel is 1.5m×1.5m. Simulation analysis.
The simulation results of the unloading condition of the chute without the central blanking funnel are shown in Fig. 3. The simulation results of the unloading condition of the chute in the case of the center blanking funnel size of 2m×2m (2m high) are shown in Fig. 4. The size of the center blanking funnel The simulation results of the unloading condition for the chute at 2m×2m (4m high) are shown in Figure 5.

Analysis and comparison of the simulation results of the three cases, can be summarized as follows:

(1) The central blanking funnel has a certain converging effect on the unloading flow, which can protect the upper chute structure from or reduce the erosion of the ore flow and prolong the service life of the chute.
(2) The smaller the cross-section size of the center blanking funnel, the stronger the convergence effect on the unloading flow: when the cross-sectional dimension of the center blanking funnel is 2m×2m, the upper structure of the chute is about 60m outside the range of the mine flushing; When the cross-sectional dimension of the center blanking funnel is 1.5m×1.5m, the upper structure of the chute is about 110m away from the scope of the mine flushing.
The determination of the cross-sectional dimension of the center blanking funnel, in addition to considering the convergence of the unloading flow, also needs to consider the needs of the maintenance and maintenance access passages of the later wells, as well as the maximum block size of the ore. The replacement of the inner liner of the lower mine silo, the lowering passage of the personnel, materials, etc. during the maintenance and repair of the chute, the cross-sectional dimension of the center blanking funnel is required to be not less than 1.5~
2m; in order to avoid the ore blocking the center of the funnel opening, the cross-sectional dimension of the center blanking funnel is also required to be not less than 3 to 4 times lower than the maximum ore block. Based on the above factors, combined with the PFC simulation results, the cross-sectional dimension of the center blanking funnel was finally determined to be 2m×2m.
2.2.2 Determination of the parameters of the center blanking funnel height
Under the premise that the cross-section size of the center blanking funnel is 2m×2m, the simulation of the height of the center blanking funnel is 2,4m. See Figure 4 and Figure 5. By analyzing and comparing the simulation results of the two cases, we can summarize the following conclusions:

(1) The influence of the height parameter of the center blanking funnel on the convergence of the unloading flow is not obvious.

(2) When the height of the center blanking funnel is large, the probability of the mines colliding with each other in the center blanking funnel increases, and the ore stream is scattered at the initial stage of unloading.
Combined with the PFC3D simulation results, the center blanking funnel height was determined to be 2 m. The funnel is made of reinforced concrete and the inner wall is provided with wear-resistant lining. Reinforce the impact load to destroy the section of the well, that is, from the unloading level of the shaft to within 40m of the shaft, adopt reinforced concrete structure, and install the wear-resistant lining on the inner wall.
3 Conclusion
Through PFC3D simulation, the movement characteristics of ore in the chute under different unloading structural parameters are analyzed, which provides an effective method for studying the migration characteristics of ore in the chute. The new unloading structure with the central falling hopper can effectively concentrate the unloading ore flow and reduce the impact damage of the ore on the upper chute.
references
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[2] Song Weidong, Wang Hongyong, Wang Xin, et al. Theoretical analysis and verification of the impact load of unloading ore in the mining area [J]. Rock and Soil Mechanics, 2011, 32(2): 326-332.
[3]ITASCAConsultingGroup, Inc. . PFC3Dtheoryandbackground[M]. Minnesota: ItascaConsultingGroup, Inc. , 2008.
[4] Wu Shunchuan, Zhou Yu, Gao Bin. Unloading rock burst test and PFC3D numerical simulation study [J]. Chinese Journal of Rock Mechanics and Engineering, 2010(9): 4082-4088.
[5] Zhu Huanchun. PFC and its application in mine caving mining research [J]. Journal of Rock Mechanics and Engineering, 2006(9):1927-1931.
Author: Wang Xiaodong; Changsha Nonferrous Metallurgy Design and Research Institute Co., Ltd;