Stability analysis of surrounding rock and dam body of underground reservoir under the influence of faults

Deep beneath the earth, where coal has been extracted for decades, vast empty spaces remain. These hollowed-out chambers, known as goafs, are often viewed as hazards, but in water-scarce mining regions, engineers see them as potential reservoirs. By transforming these abandoned underground spaces into storage tanks, miners can capture groundwater and mine water, turning a byproduct of extraction into a vital resource for production and ecological restoration. However, the rock surrounding these spaces is not a solid, unchanging shell. It is a complex geological puzzle, often fractured by natural cracks and shifted by massive geological faults—deep breaks in the earth's crust where rock masses have slipped past one another. When mining continues near these faults, the delicate balance of the underground reservoir is threatened. The weight of the rock above, the pressure of the water trapped within, and the movement of the earth itself interact in a dangerous dance of forces. If the rock fails, the reservoir could collapse or leak, turning a solution into a disaster. Understanding how these forces shift and how to keep the rock stable is the difference between a safe water source and a catastrophic failure.

Researchers set out to understand exactly how mining near a fault affects the stability of such an underground reservoir. They focused on a specific scenario where a mining face, the active edge where coal is being cut, moves toward a fault line. Using a powerful computer simulation, they built a virtual model of the underground environment, complete with layers of rock, a fault line, and the water pressure that exists deep underground. This model allowed them to watch, in slow motion, how the rock behaves as the mining face advances, step by step. They were particularly interested in the difference between mining on one side of the fault versus the other, and how the stress—the internal pressure within the rock—changes as the excavation gets closer to the break in the earth.

The simulation revealed a clear pattern in how the rock reacts. When the mining face approaches the fault from one side, known as the hanging wall, the fault acts somewhat like a barrier, holding back some of the stress. In this scenario, the rock surrounding the water storage space remains relatively stable. However, the situation changes dramatically when mining occurs on the other side, the footwall. Here, the fault does not hold back the pressure; instead, it concentrates the stress. As the mining face moves forward, the pressure builds up sharply against the fault line. This concentration causes the rock to deform and crack more easily, creating a higher risk of collapse for the water storage space. The researchers found that the closer the mining gets to the fault, and the smaller the remaining pillar of coal left between the mine and the fault, the more intense this stress becomes. The rock begins to yield, forming a zone of broken material that expands outward, threatening the integrity of the reservoir.

As the mining continues, the effects on the water itself become just as critical as the stress on the rock. The simulation showed that as the rock cracks and shifts near the fault, the pathways for water to flow open up. Pore water pressure, which is the pressure of water trapped in the tiny spaces between rock grains, begins to rise rapidly along the fault line. This rise is not steady; it happens in sudden jumps as the rock fractures and new channels form. When two mining faces work in sequence, the disturbance is even greater. The second pass of mining causes the pressure to spike again, creating a direct channel for water to rush through the fault and into the storage space. This sudden increase in water flow, combined with the weakening of the rock, creates a perfect storm for instability, potentially leading to a breach in the reservoir's containment.

To combat these risks, the researchers tested a specific engineering solution within their simulation: reinforcing the rock with bolts and cables. They modeled the installation of steel rods and cables that are drilled deep into the rock and tightened to hold the fractured layers together. The results were striking. By adding this reinforcement, the researchers were able to significantly reduce the size of the broken zone in the rock. The area where the rock had failed shrank by more than half, and the depth of the damage was kept to a manageable level. The reinforcement also helped to lower the stress concentration, spreading the pressure more evenly across the rock mass rather than letting it build up in one dangerous spot. Most importantly, the support system reduced the vertical movement of the rock, keeping the reservoir floor from sinking and cracking further. It also lowered the water pressure, effectively closing off the pathways that would allow water to surge through the fault.

The study concludes that while faults pose a serious threat to the stability of underground reservoirs, their impact can be managed with the right engineering approach. The key lies in understanding the specific behavior of the rock on either side of the fault and applying targeted support before the damage becomes irreversible. By using bolts and cables to strengthen the rock, engineers can control the movement of the fault and prevent the sudden release of water pressure that leads to failure. This work provides a clear path for designing safe underground reservoirs in fault-prone areas, ensuring that the water stored deep underground remains secure and accessible for the communities that depend on it. The findings offer a practical blueprint for turning the geological challenges of mining into a stable foundation for water conservation.