Numerical Simulation Study on Stability of Mining Columns in an Iron Mine

Iron ore body located in a marble and diorite contact zone, or within the vicinity of marble, metal contacts skarn deposit account, showing a large lens. The ore body is buried shallow, 58-162m, gradually thickening from northeast to southwest. The ore body is roughly horizontal along the lower sides of the marble bed. When the interface at the top of the diorite is bulged, the ore body is a half-moon shaped convex mirror body. The whole ore body is buried in the strike direction, with the west high and the low east. The upper part is covered by the Quaternary and rock layers, generally 40-75 m thick. The top and bottom plates are mainly marble and diorite, which are thinner. The ore block is divided along the strike, with a length of 50m and a width of 12m. The ore blocks are divided into mine houses and pillars along the direction of the ore body, and the width is 10m. The whole ore body is divided into three steps, one step back to the mining room and the pillar, and the segmented empty field method is used for recovery, and the post-filling is carried out; the second step is to recover the inter-column; and the three steps are appropriately restored to the top column under conditions.

In the mine production, the inter-column acts as the vertical support body in the direction of the stope, and bears the ground pressure in the vertical direction of the upper stratum to ensure the safety of the mining operation. At present, mining mining is nearing completion, and the mine plans to recover the inter-column. According to the calculation, the total amount of inter-column is about 1,205,300 tons. In this paper, the different inter-column mining schemes are carried out by numerical simulation.
Ratio analysis, determine the best recovery plan, and more mining under the premise of ensuring safety, improve resource utilization.
1 Model establishment and basic assumptions
A three-dimensional model is established according to the span, thickness and height of the column, and the model size is 600m×100m×100m (length×width×height). The basic assumptions are as follows:
(1) The ore body and surrounding rock are regarded as isotropic continuous media [1].
(2) Since the original rock stress is not measured in the mine, the tectonic stress is neglected when calculating the original rock stress, and the self-weight stress is calculated [2].
(3) Appropriate simplification of the inter-column model, assuming that the mine and the pillar are rectangular [3].
(4) The excavation process is completed in one time, regardless of the time effect [4].
2 Determination of rock mass parameters of model

Through the rock mechanics experiments, the relevant rock mechanics parameters are obtained. However, in order to improve the accuracy and reliability of numerical simulation, it is necessary to consider the influence of structural planes such as joints and cracks. Therefore, based on the data provided by the rock mechanics experiment, the mechanical parameters are treated [5-6], and four kinds of mechanical media are considered: the Quaternary topsoil, the upper rock mass, the ore body, the ore rock The body diorite, the mechanical parameters of the treated rock mass are shown in Table 1.

3 Determination of simulation calculation scheme
Due to the vertical ore body orientation of the column, the span is large. If all the mining is likely to affect the stability of the roof of the stope, some pillars need to be retained during the recovery of the column to maintain the stability of the roof. The numerical simulation analysis will optimize the width of the mine and the width of the pillar from the perspective of mechanical stability.
Influenced by the ore body distribution and the arrangement of the ore blocks, the span of the column varies greatly. Therefore, different simulation schemes are adopted for different spans, and the stress of the roof of the stope and the pillars are compared and analyzed. There are two options for the reserved pillars: single-column and double-column. For the inter-column with small span, single-column column is adopted, and for the inter-column with large span, double-column is adopted.
In this paper, only the large-span inter-column mining is simulated, that is, the double-column scheme is adopted. The final plane of the inter-column mining is shown in Figure 1. The simulation parameters are shown in Table 2.

4 simulation calculation results and analysis
After mining of three different parameters of the mine, the maximum principal stress distribution characteristics of the roof are shown in Figure 2. It can be seen that under the three kinds of conditions, the top plate of the stope is subjected to a certain tensile stress, and the tensile stress of the middle mine roof is significantly larger than that of the two sides, and the maximum tensile stress is located at the center of the middle mine roof. As the width of the pillar increases and the width of the mine decreases, the maximum tensile stress decreases gradually, which are 1.84, 1.51, and 1.37 MPa, respectively.

Figure 3 is a plot of the vertical displacement contour of different width mines and pillars. It can be seen that the top and bottom plates of the stope have a certain displacement, and the displacement directions are all directed to the stope. The displacement distribution of the top and bottom plates of the three different schemes has the same law. The displacement of the roof of the intermediate mine is obviously larger than that of the two sides of the mine. The maximum displacement is located at the center of the middle mine, which almost covers the roof of the entire stop. As the width of the pillar increases and the width of the mine decreases, the maximum displacement of the roof decreases gradually; the displacement distribution of the floor is generally the same, and the maximum displacement is located at the center of the floor and decreases toward the periphery.
5 Conclusion
(1) When the width of the mine is 39, 37, 35m, the maximum principal stresses are 1.84, 1.51, 1.37MPa, respectively, and the maximum tensile stress value decreases gradually, and the reduction is also significantly reduced. Within a certain range, reducing the width of the mine can effectively improve the stress of the roof. As the width of the mine continues to decrease, the improvement of the roof's stress conditions is significantly weakened.

(2) stope width is 39m, the maximum tensile stress value of the top plate being 1.84MPa, 1.89MPa tensile strength of roof near the body, since the numerical simulation of the mining operation is not caused by disturbance considered stope Therefore, in order to ensure the safety and stability of the roof of the stope, it is recommended to adopt the scheme II, that is, the pillar width is 15m and the mine width is 37m.
(3) According to the analysis of the maximum principal stress and vertical displacement, the top roof of the intermediate mine is the area of ​​maximum tensile stress and maximum displacement. The stability of the roof of the stope is relatively poor compared with the two sides of the mine. In the actual production, the intermediate mine should be strengthened. Support and monitoring of roof panels.
references
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