Discharge Capacity of the Flood Discharge Shaft in a Tailings Reservoir: An Experimental and Numerical Study

In China, tailings reservoirs often experience failure events due to inadequate discharge capacity or flood discharge system failures. To ensure the safe and reliable operation of the flood discharge system in a tailings reservoir, this study investigated the discharge capacity of a tailings reservoir in Henan Province, China, through hydraulic model tests and numerical simulations conducted using FLOW-3D. The results indicated that when the water head was below 0.8 m, the flow was in a non-pressurized regime with low discharge capacity. As the water head increased to 0.8–1.2 m, air began to be entrained into the flow, leading to an alternating regime between open-channel flow and full-pipe flow. Once the water head exceeded 1.2 m, the flow expelled air and transitioned into a pressurized full-pipe regime. At a water head of 1.6 m, the flow was in a pressurized full-pipe regime. The experimental flow rate, flow velocity, and flow regime of flood discharge shaft No. 1 closely matched the simulation results. Additionally, the discharge capacity of the shaft increased as the height of the discharge window was raised. The discharge capacity and flow velocity of the discharge windows on the eighth layer were 30.1% and 29.2% higher, respectively, than those on the first layer, which indicated that the system’s drainage capacity increased as the shaft length increased. However, increasing the height of the discharge window increased the likelihood of an alternating regime between open-channel flow and full-pipe flow. During the operation of the tailings reservoir drainage system, it is essential to ensure that the upper-layer discharge windows are functioning while minimizing the occurrence of unfavorable flow regimes. The discharge water head should be controlled to remain below 0.8 m. These operations not only ensure that the discharge capacity meets the requirements but also enable the drainage tunnel to operate safely and effectively over the long term. The findings of this study can provide a scientific basis for the design and safe operation of tailings reservoir drainage systems.