Experimental study on mining method of a limestone mine

With the rapid development of the national economy, limestone is an important building material and the main raw material for the production of cement, and the demand is increasing. Limestone is a kind of sedimentary rock, which is mostly thick and layered. It is produced by block structure and is generally extracted by open-air method. However, due to the limitations of mining technology conditions, such as the protection of natural ecological environment, the surface is not allowed to be destroyed, and the underground mining of limestone mines is developing rapidly in some areas. A few large limestone underground mines are mined by a more formal segmentation method or a retention method, and the economic benefits and safety are relatively good. However, due to insufficient technical strength, the small private limestone underground mines are mostly shallow-hole room-column methods with irregular ore pillars. There are labor intensity, low production efficiency, poor ventilation conditions, unreasonable stope structure, and resource recovery. Low rate and other disadvantages [1-2]. Therefore, it is very important and necessary to improve the technical level of such mining, improve production efficiency, improve ventilation, improve resource recovery rate, and ensure safe production of mines.
1 Mine Overview
A limestone deposit occurs in the carbonate strata of the Lower Permian Qixia Formation and is distributed in the NE-trending anticline structure, with a thick layered output, which is consistent with the stratigraphic structure. The axial direction is northeast-southwest and tends to be inclined to the southeast and northwest respectively. The inclination angle of the two wings is 45°~49°, and the maximum length of the ore body is 1060m, and the width of the plane is distributed.
It is 250-490m, the area is about 0.375km2, the control thickness is generally 16.85~114.17m, and the maximum thickness in the shaft is 114.17m. The thickness of the ore layer is large and continuous. The deposit is a polygon on the plane, which approximates a top-surface undulating "skull body".

The limestone rock structure is dense, the joint cracks are not developed, the compressive strength is 62.2-63.6 MPa, and the firmness coefficient is 5-10. The ore is intact, hard and stable, and has good engineering performance. Generally, it is not supported.

Due to the technical constraints of mining, the limestone mine is underground. The design mining elevation is +20~-25m, the production scale is 400,000t/a, and the ramp road-car development transportation scheme is adopted. The original mining method is the ordinary shallow hole room column method, that is, shallow hole rock and rock collapse, excavator loading and mining, and dump truck transportation. The ore blocks are vertically oriented, and each block is divided into three parts: the mine room, the column and the top column. The column and the top column are permanent pillars and are not harvested.
2 mining method selection
In order to solve many problems existing in the mining process of ordinary shallow hole room and pillar, and to achieve safe and efficient mining, the mining method selected should meet the conditions of large capacity of the ore block and good ventilation safety. Combined with the thickness of the ore limestone ore body and the characteristics of the trackless equipment, the pre-cutting top-down parallel medium-deep hole room column method and the upward fan-shaped medium-deep hole room column method were preliminarily selected.
Scheme I is a pre-cut top to bottom parallel deep hole chamber method. Divide the mine into two layers of upper and lower layers. A Boomer281 drilling rig is used to dig a cut-top roadway at the top of the mine to form an upper tiered pedestrian, ventilation, transportation and safety exit passage. The section of the cut roadway is a three-hearted arch with a size of 4m×3.5m (width×height); the top roadway is gradually brushed to the two sets to form a 15m×5m (width×height) cutting head space, and the upper layer is completed. The mining work [2]; using the TamrockRanger600 type down-the-hole drilling rig to drill a depth of 10m to the parallel medium-deep hole in the top-cut space, the differential blasting, the caving of the ore is loaded with excavators, and the load dump truck is transported by the slope. Out of the ground, complete the mining work under the stratification. The technical scheme of Scheme I is schematically shown in Figure 1.
Scheme II is an upward fan-shaped medium deep hole room column method. In one step, the rock drilling, loading and transportation work is completed in the rock drilling roadway at the bottom of the mine. Using a shallow hole rock blasting, a rock drilling roadway is drilled at the bottom of the mine as a pedestrian, ventilation, rock drilling, slag discharge and safety passage. The roadway section is a three-heart arch with a size of 4m×3.5m (width×height); In the rock drilling roadway, the YGZ-90 rock drilling rig (with TJ25 type drilling rig ) is used to drill the upper fan-shaped medium-deep hole, and the BQ-100 type chargeer is used to charge and cut into the pre-prepared cutting groove. The collapsed ore is loaded with a ZL50C loader, and the 10t dump truck is transported out of the surface via a ramp. The technical scheme of Scheme II is shown in Figure 2. The characteristics, advantages and disadvantages of I and II technical solutions are shown in Table 1.

Through comprehensive comparison of schemes I and II, it can be judged that the advantages of scheme I in mining rock drilling efficiency, production capacity and ventilation safety are obvious. Therefore, this project selects the pre-cut top-down parallel parallel deep-hole room column method to carry out experimental research.
3 medium and deep hole room method test
3.1 Test location
The test stope is arranged near the 0# exploration line and on both sides of the 0~-25m slope. The ore type is marble and limestone. The ore is hard and stable, continuous and complete, the joints are not developed, and the engineering conditions are good.
3.2 Test nugget components
A piece of ore is divided into three parts along the ore body every 30m, divided into three parts: the mining room, the column and the top column. The length of the mine is 80-100m, the width is 15m, the height is 18m, the column width is 15m, and the top column is 30m thick. The mining room is divided into two layers, the upper layer is 8m high and the lower layer is 10m high. The mining method is shown in Figure 3.

3.3 mining process
The mining room is first stratified and then stratified [3]. The upper layer mining is actually forming a roof-cutting space, creating conditions for the lower layer mining.
3.3.1 Upper layer mining
Firstly, the pre-cutting top roadway is pulled along the long axis of the ore block at the upper layer +10m level, and the two ends are respectively connected with the +10m middle section of the transportation roadway and the return airway to form an upper layer of pedestrian, transportation, ventilation and safety exit channels. . The cross section of the pre-cut roof is a three-hearted arch with a size of 5m×6m (width×height); the top-cut space is formed by the expansion of the pre-cutting roadway, and the layered blasting is carried out on the inclined working face or the retained ore pile. Advance layer by layer [4], and finally form a 15m × 8m (width × height) cutting space. The caving ore is transported by excavator loading and dumping and transported directly to the surface crushing station via the main ramp. After the topping space is formed, the upper layering recovery work is completed.
3.3.2 Lower stratification recovery

Before the next layer of mining, the next layer of the development of transport roads and mining cutting work. The slope is developed from the elevation of +10m to the elevation of 0m. A horizontal transportation roadway is connected from the 0m elevation to the mining area of ​​each test stop. The lower horizontal transportation roadway is arranged in the middle part of the mining room as a pedestrian in the lower layer. , transport, ventilation and safe exit channels. Thus, a 5m×6m×10m (length×width×height) vertical trough is formed in the middle part of each mine, which serves as the free surface and compensation space for the collapse of the mines at both ends of the lower layer. The rock drilling equipment is a TamrockRanger 600 type down-the-hole drilling rig with a blast hole inclination angle of 90°, a hole diameter of 79 mm, a hole depth of 10 m, a hole spacing of 3.0 m, a row spacing of 2.5 m, and an explosive unit consumption of 0.6 kg/m3. 2# rock explosive, continuous column charge, non-conducting blast pipe detonator detonation, segmentation time is 50ms [5]; the collapsed ore is directly loaded with PC-200 excavator, 10t dump truck is transported to Surface crushing station; large ore is equipped with excavator to install E200B hydraulic crusher for secondary crushing.
3.4 stope ventilation
When lining the pre-cut roof roadway, the main fan ventilation is adopted. After the pre-cut top roadway is pulled through, a mechanical extraction of the main fan of the mine is used to form a through-flow ventilation [5]. The fresh air flow enters the stope from the +10 and 0m horizontal transportation lanes, and the dirty wind is sent from the pre-cutting roadway into the return airway to discharge the surface. In order to quickly discharge smoke and reduce dust, enhance ventilation
If a local fan is used for auxiliary ventilation.
3.5 top board management
In the upper layer mining, the top plate inspection equipment is used to clean the top stone, and a welded iron basket is installed in the excavator bucket. The safety personnel stand in the iron basket held by the excavator and carry the skid stick to check the pumice . Using the self-made equipment instead of the top board to check the lifting trolley, not only saves equipment investment, but also is easy to operate, safe and reliable. When the next layer is plucked, the roof is inspected before entering the stope operation to ensure safe entry into the stope.
4 test results
The project has arranged five test sites in the middle section of 0m in the east mining area, and carried out the 2a medium deep hole room column test. According to statistics, the production capacity of the test stope has increased from 200t/a to 1000t/a, the mining efficiency has increased from 40t/a to 200t/a, and the resource utilization rate has increased from 25% to 40%. 150,000 t. The direct cost of mining was reduced from 11.8 yuan/t to 9.3 yuan/t, and the annual mining cost was about 500,000 yuan. The ventilation effect of the stope was obviously improved, and the working time of the workers under the roof was reduced, and no safety accident occurred during the period.
5 Conclusion
Combined with the technical conditions of a subterranean limestone mining, the pre-cutting top-to-parallel medium-deep hole chamber column method is selected to be divided into two layers, and the upper layer is used for mining to form the cutting head space, which provides conditions for the lower layer to adopt the medium-deep hole step blasting. , use non-track, large-scale, mechanized rock drilling, shovel loading, transportation equipment. Through the test of 5 stope, it is proved that the mining method has the advantages of large production capacity, low mining cost and good ventilation safety conditions. Because the lower layer mining operation is carried out under high and empty space, the roof inspection and treatment is more difficult. In the production process, the roof inspection should be strengthened to prevent the top plate from loosening the pumice and causing a safety accident. The pre-cut top-to-parallel medium-deep hole chamber column method can obtain the expected test results, which is suitable for popularization and application in the stable limestone underground mine.
references
[1] Chen Hongan. Application of a room-column mining method layout in limestone ore mining [J]. Fujian Building Materials, 2007 (2): 40-41.
[2] Wang Chunhua. Research on safe and efficient pit mining technology of limestone mine [D]. Zhangzhou: Jiangxi University of Technology, 2012.
[3] Chen Min, Shi Xiuzhi. Numerical simulation of structural parameters of a limestone mine stope [J]. Mining Technology, 2015, 15(1): 16-17.
[4] Shang Yufeng. Research on mining methods of limestone underground mines [J]. Mining Express, 2008 (4): 52-54.
[5] Huang Tieping, Wang Chunhua. Test and analysis of deep hole blasting vibration in a limestone underground mine [J]. Southern metal, 2011 (4): 31-33.
Article source: "Modern Mining", 2017.4
Author: Chen Min, Huang Tieping; Metallurgical Construction Design and Research Institute of Guangdong Province Copyright:

1.Design speed: 250m/min.Width:2000mm