Underground Fractured Caverns: Definition and Core Functions

In underground mining operations, the underground crushing chamber is a specially designed facility that serves as the critical hub for conducting the essential secondary crushing of large rock fragments from the mining face. Often referred to as the "chokepoint" of the mine, this chamber plays an indispensable role throughout the entire mining process. During underground extraction, blasting typically leaves behind sizable chunks of ore. If these oversized pieces were directly transported, they would pose significant challenges for subsequent hoisting and transportation systems—potentially leading to blockages or even damaging equipment. This is precisely where the underground crushing chamber comes into play. Its primary function is to use specialized crushing equipment to reduce these large ore fragments into smaller, more manageable sizes that meet the requirements of downstream hoisting and transport systems. Typically, after crushing within the chamber, the ore particles are reduced to no larger than 350 millimeters—ensuring they can be efficiently lifted by skip hoists or conveyed via conveyor belts, thereby keeping the entire mining operation running smoothly.

From a functional perspective, the core task of underground crushing chambers is to efficiently and safely carry out the secondary crushing of ore. In this process, it’s essential to carefully select and properly arrange the crushing equipment to ensure optimal crushing performance and production efficiency. Commonly used crushing equipment includes jaw crushers, gyratory crushers, and more. At the same time, attention must also be paid to constructing supporting facilities such as ventilation, drainage, and rock support systems, which provide a favorable working environment for crushing operations while safeguarding the safety of both personnel and equipment. For instance, an effective ventilation system can promptly remove dust and harmful gases generated during crushing, minimizing their impact on operator health; meanwhile, robust support structures help prevent chamber collapse, ensuring that operations remain safe at all times.

Significant Advantages and Challenges: The Duality of Underground Fragmentation

Three core advantages empowering efficient mining

Compared to the traditional practice of secondary blasting and crushing during mine extraction, underground crushing chambers centralize and mechanize the crushing process, significantly reducing both the number and duration of on-site blasting operations. For instance, at a large-scale metal mine, before the introduction of underground crushing chambers, secondary blasting in the mining area frequently interrupted ore extraction, allowing only about 500 tons of ore to be produced per shift on average. However, after adopting underground crushing chambers—and leveraging continuous operations from equipment such as jaw crushers and gyratory crushers—the mine’s ore output per shift surged to 800–1,000 tons, dramatically boosting extraction efficiency. This not only enhanced the overall production capacity of the mining area but also provided robust support for the mine’s large-scale exploitation efforts.

Secondary blasting in mining areas often requires frequent use of explosives, posing significant safety risks such as flying rocks and toxic fumes from blast gases. In one mine project I once worked on, flying rocks from a secondary blast struck equipment, resulting in severe financial losses. By contrast, underground crushing chambers relocate the crushing operations to dedicated spaces, minimizing direct contact between personnel and blasting activities while also preventing blast vibrations from compromising the stability of surrounding rock in the mining area—thus reducing safety risks at their source. Moreover, these chambers can be equipped with comprehensive safety features, such as advanced ventilation systems and dust-control devices, providing workers with a far safer and more secure working environment.

By controlling the crushing granularity, we ensure that the ore meets the requirements for skip hoisting or belt transportation, reducing wear on lifting equipment and minimizing efficiency losses caused by uneven block sizes. This approach enables a seamless integration of the mine's logistics system. In actual production, we've observed that after processing in the underground crushing chamber, ore transport becomes smoother, and equipment failure rates drop significantly. As a result, not only is transportation efficiency improved, but equipment maintenance costs are also reduced, ultimately leading to optimized resource utilization.

Three Major Real-World Challenges That Require Targeted Responses

The crushing chamber requires the excavation of a large-section tunnel, with its width and height designed to accommodate equipment installation and maintenance needs. For instance, in one mine, the underground crushing chamber boasts a width of 8 to 10 meters and a height of 6 to 8 meters—clearly a structure that poses significant construction challenges and incurs high costs. Moreover, this type of large-section tunnel also necessitates complementary ancillary facilities, such as unloading chambers, ore bins, and ventilation shafts. As a result, the initial infrastructure workload increases by 30% to 50% compared to surface-based crushing stations, leading to a substantial rise in investment costs. For some mining enterprises already facing financial constraints, this presents a considerable challenge.

In the enclosed underground environment, dust generated during crushing operations tends to accumulate easily, and mechanical vibrations combined with equipment operation can further intensify dust dispersion. If the ventilation system is improperly designed, it may lead to excessive dust concentrations in the chamber, posing serious risks to both workers' health and the longevity of equipment. For instance, there was once a mine where an inadequate ventilation system resulted in chronically high dust levels inside the chamber, causing numerous workers to develop pneumoconiosis. Additionally, equipment frequently broke down due to dust-related corrosion. To address this issue, it’s essential to equip the space with dedicated dust-control equipment and an independent ventilation system—such as installing high-power ventilators and integrating effective dust removal devices—to ensure that air quality within the chamber consistently meets safety standards.

The damp and dusty underground environment accelerates equipment aging, while the limited space in crushing chambers makes it necessary to rely on auxiliary tools like overhead cranes for large-scale equipment maintenance—resulting in far lower repair convenience compared to surface facilities. Equipment failures can even lead to a complete shutdown of the entire mining area, placing extremely high demands on operational maintenance expertise and spare parts inventory. In my experience at work, an equipment malfunction once caused the entire mining area to halt production for two days, inflicting significant financial losses on the mine. Therefore, mining companies must establish comprehensive equipment management systems, strengthen daily maintenance and upkeep of their machinery, and ensure adequate stockpiles of spare parts to promptly address any unexpected equipment breakdowns.

Layout Form Analysis: Engineering Choices Tailored to Local Conditions

Decentralized Lateral Type: Flexibly Adapts to Distributed Mining Areas

The decentralized lateral arrangement involves independently setting up crushing chambers along the sides of each mining district, primarily serving either a single or adjacent mining areas. This layout is akin to placing a small-scale crushing station right "at the doorstep" of each mining zone, enabling on-site processing of ore and significantly reducing short-distance transportation needs. Take, for instance, a certain small-scale lead-zinc mine characterized by dispersed ore bodies distributed across multiple narrow veins, with considerable height differences between mining stages. After adopting the decentralized lateral arrangement, crushing chambers were strategically positioned near each ore vein. As soon as the ore was extracted, it could be swiftly transported to the nearest chamber for crushing—effectively addressing the challenges of high costs and low efficiency associated with long-distance transportation. This approach is particularly well-suited for mines with scattered ore bodies and significant stage height variations, making it a common choice for medium- to small-sized mines or projects involving long, segmented mining operations.

Centralized Sideways Layout: The Efficiency Choice for Scalable Production

The centralized side-by-side arrangement involves centrally locating crushing chambers adjacent to the main decline shaft or main transport roadway, serving multiple mining areas or levels simultaneously. This layout essentially integrates several small-scale crushing stations into one large, centralized crushing hub, where ore from various mining zones is transported for unified crushing operations. Many large copper mines have adopted this configuration due to their high annual production volumes and concentrated mining layouts. By employing the centralized side-by-side setup, ore from multiple mining areas is routed via the main decline shaft or primary transport roadway directly to the central crushing chamber, allowing shared use of crushing equipment and ancillary facilities. This approach not only reduces the per-unit cost of ore crushing but also facilitates streamlined management of equipment and production processes, ultimately boosting overall efficiency. It is therefore an ideal choice for medium- to large-scale mines characterized by high annual output and clustered mining areas.

Sub-underlying orebody centralized layout: Engineering arrangement prioritizing stability

The centralized layout beneath the ore body involves placing crushing chambers within the stable rock layers of the ore body's footwall, while ensuring they are kept well away from faults, fracture zones, and water-bearing areas. At the core of this arrangement is leveraging the inherent stability of the footwall rock to provide robust support for the crushing chambers, thereby reducing chamber-support costs and ensuring long-term operational reliability. For instance, a large gold mine successfully implemented this centralized footwall layout after conducting thorough geological exploration to pinpoint the exact location of the stable footwall rock formations. Although connecting the crushing chambers to various mining levels via decline shafts or transport drifts added some engineering complexity, the approach effectively capitalized on the stability of the footwall rock, significantly cutting down on support expenses and guaranteeing the safe operation of the crushing facilities. However, this layout method places stringent demands on the geological conditions of the rock formations, making it essential to carry out comprehensive geological surveys and analyses before making a selection.

System Composition and Key Equipment: The "Rugged" Support Behind Underground Crushing

Core Process System Components

The unloading chamber serves as the "entry point" where ore enters the crushing process, completing the unloading of ore transported directly from the mining face. The feeding equipment acts like a precise "conveyor," precisely controlling the flow by opening and closing gates, while ensuring smooth operation through either a plate feeder or a vibrating discharge machine—both of which steadily deliver ore in a uniform and continuous manner to the next stage of crushing equipment. The plate feeder boasts a robust design, perfectly suited for handling large chunks of ore with reliability and stability, whereas the vibrating discharge machine leverages efficient vibration technology to achieve rapid, even material distribution. In actual operation, the reliable performance of the feeding equipment is absolutely critical, as it directly influences the efficiency of the crushing machinery. Any inconsistency in feeding can lead to issues such as blockages or overloads in the crushing equipment, ultimately disrupting the smooth flow of the entire crushing process.

Crushing equipment serves as the "central brain" of underground crushing chambers, with the mainstream options being jaw crushers and gyratory crushers. Jaw crushers are ideal for the secondary crushing stage, capable of handling ore pieces up to 1,200 mm in size. They feature a simple design and reliable operation, using the periodic swinging motion of the moving jaw to crush, bend, and split the ore. On the other hand, gyratory crushers excel at primary crushing, processing ore pieces up to 1,500 mm in size. These machines rely on the rotation of an eccentric sleeve, which drives the movable cone into a conical motion, continuously squeezing and grinding the ore. Gyratory crushers offer advantages such as a deep crushing chamber, high production capacity, and uniformly sized final product. To further enhance crushing efficiency, fixed screens are typically installed upstream of the crushing equipment to pre-screen the ore. This process separates ore particles that already meet the desired size specifications, preventing them from entering the crusher and reducing unnecessary wear and tear on the machinery. As a result, overall crushing efficiency is significantly improved.

After being crushed, the ore requires a "temporary holding point," and the lower ore bin plays this role by serving as a temporary storage area for the crushed material. To precisely control the amount of ore lifted, the system is equipped with measuring devices such as electronic belt scales, which continuously monitor and record the weight of the ore in real time, providing accurate data support for subsequent production scheduling. Once measured, the ore is hoisted to the surface either via skip buckets or conveyor belts. Skip bucket systems offer the advantages of rapid lifting speed and high transportation capacity, making them ideal for large-scale mines. In contrast, conveyor belts are renowned for their continuous operation and exceptional reliability, making them widely used in mines with higher production volumes and longer transportation distances. Additionally, some mines also install overhead cranes to facilitate equipment maintenance and replacement, ensuring that any malfunctions can be promptly addressed, minimizing downtime and maintaining seamless production continuity.

Key Points in Underground Chamber Engineering Design

The geological environment surrounding underground fractured caverns is highly complex, with factors such as ground pressure and blasting vibrations constantly threatening the cavern's safety. Therefore, the design of the support structure is absolutely critical. Typically, either reinforced concrete monolithic support or shotcrete-anchor-net support systems are employed. Reinforced concrete monolithic support acts like a robust "armor" enveloping the cavern, effectively resisting both ground pressure and dynamic loadings from vibrations. In contrast, shotcrete-anchor-net support leverages the synergistic effect of anchor bolts, steel mesh, and sprayed concrete to enhance the natural self-stability of the surrounding rock mass, seamlessly integrating the rock with the support structure into a unified whole. Meanwhile, in areas characterized by high stress, additional anchor cables are installed for reinforcement—these cables serve as sturdy "anchor piles," penetrating deep into the surrounding rock to deliver powerful anchoring forces, thereby further ensuring the cavern's resistance to vibration and long-term stability.

The ventilation system is the "respiratory system" of underground crushing chambers, and its design directly impacts both the health of workers and the proper functioning of equipment. Since crushing operations generate significant amounts of dust, failure to remove it promptly can severely damage workers' respiratory systems and also shorten the lifespan of machinery. Therefore, it's essential to establish dedicated exhaust tunnels equipped with high-power axial fans, creating robust ventilation dynamics that draw fresh air into the chamber while efficiently expelling dust-laden exhaust gases. To effectively reduce dust concentrations, baghouse dust collectors are installed to purify the outgoing air, ensuring that dust levels remain below 2 mg/m³—thus meeting occupational health standards and providing workers with a safe, healthy working environment.

Engineering Case Study: A Comprehensive Analysis of a Mine's Crushing and Screening System全流程

Taking a certain metal mine as an example, its stope system is arranged along the -230m to -509m mid-levels, with the core process outlined as follows:

1. Ore unloading stage: Ores from the -230m and -270m levels are discharged into the main chute via the unloading chamber, then allowed to descend by gravity through the chute to the crushing chamber at -380m.

2. Crushing Process: The ore is screened through a fixed screen; larger chunks are fed into a jaw crusher for crushing, while the qualified ore falls into the lower storage bin.

3. Enhanced Transportation: The -459m metering chamber precisely controls the ore feed rate, which is then conveyed via conveyor belts to the -480m main shaft bottom. From there, hoisting skips transport the ore directly to the surface. This system, featuring a centralized side-by-side layout, achieves a daily processing capacity of 12,000 tons of ore—representing a 40% improvement in crushing efficiency compared to conventional mining operations. However, it’s important to optimize ventilation in the -380m intermediate connecting roadway and ensure regular equipment inspections.

Practical Insights: Key Considerations for the Design and Operation of Underground Fractured Chambers

Scientific site selection, laying a solid foundation for stability

In the construction of underground mining chambers, site selection is the primary and critical step. Priority should be given to avoiding geologically weak zones, such as fault zones and fracture zones, as these areas suffer from poor rock stability and frequent ground pressure activities, making chamber collapse and deformation highly likely—thus posing serious risks to equipment and personnel safety. For instance, at a certain mine, improper site selection during initial construction, specifically locating the chamber near a small fault, resulted in localized roof collapses shortly after operation began. This not only caused significant damage to equipment but also led to an extended shutdown for repairs and reorganization. Therefore, when choosing a site, it is essential to rely on comprehensive geological surveys to gather accurate data, providing a scientific basis for informed decision-making. At the same time, efforts should be made to position the chamber as close as possible to the main shaft or primary transport tunnels, which can significantly shorten ore transportation distances, reduce both costs and transit time, and ultimately enhance overall production efficiency.

Precise selection, tailored to ore characteristics

Equipment selection directly impacts both crushing efficiency and production costs. Ore hardness is a critical factor in making the right choice: generally speaking, ores with a Pugh coefficient of f = 8–20 are classified as hard rocks. For these types of hard rocks, a gyratory crusher is an ideal option, as it delivers powerful crushing force, effectively handling large, tough rock pieces and ensuring efficient operation of the primary crushing stage. Meanwhile, for medium-hard rocks (Pugh coefficient f = 3–8), jaw crushers excel due to their simple structure and reliable performance, enabling stable secondary crushing operations. At a certain quartz mine, the ore proved to be particularly hard (with a Pugh coefficient of around 15), yet the initially selected impact crusher turned out to be unsuitable. This led to severe equipment wear, frequent maintenance needs, and ultimately, low production efficiency. After switching to a gyratory crusher, however, the crushing performance improved significantly, while the equipment failure rate dropped dramatically.

Smart upgrades, leading to efficient operations and maintenance

With the continuous advancement of technology, intelligent upgrades have become an inevitable trend in the development of underground crushing chambers. The introduction of vibration monitoring systems enables real-time capture of equipment vibration data. By analyzing this data, potential equipment faults—such as bearing wear or component loosening—can be identified promptly. Meanwhile, the real-time dust concentration monitoring system provides 24-hour, uninterrupted surveillance of dust levels inside the chamber. If dust concentrations exceed safe thresholds, the system immediately activates appropriate dust suppression measures, ensuring the health and safety of operational personnel. Combined with PLC-based automated control technology, the crushing process can now be remotely regulated. Operators at the ground-level control center can adjust critical equipment parameters—including ore feeding rate and crushing intensity—while also benefiting from advanced fault-warning capabilities. Should any abnormalities occur, the system instantly triggers alarms, alerting maintenance teams to address issues promptly, thereby significantly enhancing both the safety and stability of production operations.

Conclusion

Underground fractured chambers are a key indicator of efficient production in modern mines, and their design and application require finding the optimal balance among efficiency, safety, and cost.