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Medium-Depth Hole Blasting for Ore Extraction—Black Diamond Broadcast
01
Core Equipment for Medium-Depth Downhole Mining: Selection and Application of Rock Drills
In medium- and deep-hole mining operations, the selection of rock-drilling equipment is crucial, as it directly affects drilling efficiency and quality. Commonly used medium- and deep-hole rock-drilling equipment includes rock drills such as YG-40, YG-80, YG-90, and YGZ-90. Among these, the YGZ-90 rail-mounted rock drill is widely applied in mining operations; it can be used in conjunction with... CTC14A It is compatible with either the CTC142 rock drill rig or the TJ25 rock drill and is suitable for harder or extremely hard rock formations (F = 8–18). It can drill blast holes with diameters ranging from ∮50 to ∮80 mm, with an effective hole depth of up to 30 meters. This equipment features high torque for rotating the drill bit, making it less likely to get stuck when drilling into rock formations containing cracks or cavities. Even if it does occasionally get stuck, the problem can be easily resolved by using a combination of weak impacts and strong rotation. Moreover, it has a wide range of adaptability to axial thrust, is easy to operate, and allows users to adjust the impact energy, drill bit rotation speed, and axial thrust according to the specific characteristics of different types of rock, thereby achieving higher drilling speeds.
02
Charging Process: Proper Use of the Charging Device and Key Points for Loading Ammunition
Charge loading is one of the key steps in medium-deep hole mining, and whether the charging device is used correctly directly affects the blasting results. Currently, the FZY-10 charging device and the BQ-100 charging device are widely used in mines. When using a charging device, first check that the equipment is in good condition and ensure that the air lines and pipelines are unobstructed. During the charging process, it’s important to carefully control both the charging speed and the amount of charge loaded, avoiding situations where the charge is either too dense or too sparse. For medium-deep holes with fan-shaped blast patterns, since the conditions at the hole mouth and the hole bottom differ, special attention should be paid during charging to appropriately reduce the charge density in the hole-mouth area, thus preventing excessive concentration of explosives at the hole mouth. Meanwhile, in the hole-bottom area, the charge should be reasonably increased according to the actual situation, ensuring that the explosive energy is evenly distributed throughout the hole and laying a solid foundation for subsequent blasting effects.
In actual operations, we’ve encountered problems caused by improper handling of the charging device. Once, during a mining operation, the operator failed to check the charging device’s air lines in advance, resulting in unstable air pressure during the charging process and inconsistent charge amounts—sometimes too much, sometimes too little. As a result, after blasting, the ore in certain areas was not crushed effectively, leaving many large chunks that hampered subsequent mining efficiency. Therefore, it’s truly crucial to follow the operating procedures for the charging device meticulously; every small detail can determine the success or failure of the entire blasting operation.
03
The Challenge of High-Ratio Blocks: Cause Analysis and Response Strategies
(1) Causes of the large-scale rate
When using fan-shaped blast-hole patterns for medium-to-deep hole mining, large fragments are prone to form after blasting. The main reasons for this phenomenon are as follows: From the perspective of explosive distribution, the fan-shaped pattern results in an uneven distribution of explosives within the holes—denser explosives at the hole mouths and easier breakthrough between holes—thus concentrating energy forward and pushing out large fragments. From the standpoint of hole spacing design, if the distance between hole bottoms is relatively large, even a deviation of just 1° or 2° in the hole angles can lead to uneven stress distribution in the rock at the hole bottom during blasting, resulting in larger fragments. Furthermore, under fan-shaped blast-hole conditions, the propagation and superposition effects of stress waves during blasting are less than ideal, which can also cause insufficient fragmentation of rock in certain areas, thereby forming large fragments.
(2) Small Resistance Line Technology Reduce the rate of large blocks
To reduce the occurrence of large fragments, the small stemming resistance technique is often employed. This technique involves reducing the minimum stemming resistance and increasing the hole spacing while keeping the area of the blasthole pattern (hole spacing a × minimum stemming resistance W) and the unit explosive consumption essentially unchanged, thereby achieving the following: Borehole density coefficient m = a/W = 3~6. The principle behind this approach is that reducing the minimum resistance line allows the stress wave to concentrate its energy more effectively as it propagates through the rock, resulting in a more intense fracturing effect. Meanwhile, increasing the spacing between boreholes enables the blast-induced stress waves to overlap more rationally between holes, leading to a more uniform rock fragmentation. In practical applications, starting from the rock-drilling center identified in the tunneling roadway, boreholes are arranged radially, first placing the corner holes and then evenly adding the remaining boreholes according to the selected maximum hole spacing. This ensures that the borehole layout is reasonable and that the explosive energy can be fully applied to the rock, thereby effectively reducing the occurrence of large-sized fragments. 
04
Borehole Arrangement Method: Characteristics and Applications of Horizontal and Upward Fan-Shaped Arrangements
(1) Horizontal fan arrangement
The horizontal fan arrangement is a pattern for drilling in medium-to-deep holes, where the blast holes are arranged horizontally in a radial fashion, using the rock-drilling drift as the reference point. This arrangement is suitable for certain specific orebody geometries—for instance, when the orebody exhibits a certain degree of continuity and regularity in the horizontal direction. When laying out the holes, start from the center of the rock-drilling drift and arrange the blast holes horizontally at a fixed angle and spacing. However, the horizontal fan arrangement has certain limitations in practical applications: due to the horizontal distribution of the blast holes, the fragmentation effect on the overlying and underlying rock layers may not be optimal, and it places high demands on the horizontal positioning accuracy of the rock-drilling equipment.
(2) Arranged in an upward fan shape
The upward fan-shaped arrangement is widely used in medium-to-deep hole mining, with blast holes arranged in a fan-like, radiating pattern pointing upward. The advantage of this arrangement lies in its ability to better accommodate the geological conditions of most ore bodies—particularly when the ore body has a certain dip angle or when there are differences in rock properties between the upper and lower layers. By arranging the blast holes upward, the energy from the explosives can more effectively act on the overlying rock, enhancing the fragmentation effect. During construction, starting from the center of the rock-drilling point, the blast holes are arranged upward according to the designed angles and spacing. First, the positions of the corner holes are determined, and then the intermediate holes are evenly distributed, ensuring that the distribution of blast holes within the entire fan-shaped area is reasonable. This guarantees uniform fragmentation during blasting and reduces the formation of large boulders.
