Study on Blasting Parameter Optimization and Vibration Control for Large-section Excavation of Spillway Tunnels in Baihetan Hydropower Station

To address technical bottlenecks in flood discharge tunnel projects for large hydropower stations, such as difficulty controlling over-excavation and vulnerability to surrounding rock damage, an innovative three-in-one construction technology system consisting of “three-dimensional layered control-composite blasting system-dynamic parameter optimization” was proposed. Firstly, based on the geological characteristics of the flood discharge tunnel at the Baihetan Hydropower Station, a layered excavation model was constructed. The first layer, with a height of 8 m, employed a pilot drift and side wall expansion excavation method; The second layer, with a height of 9m, served as the core blasting layer; and the third layer, with a height of 3 m, was the floor protection layer. Secondly, the “presplitting-buffering-main blasting” coordinated blasting technology was adopted, incorporating multiple blasting methods such as deep-hole bench blasting and presplitting blasting. Meanwhile, the main blasting holes adopted a continuous charge structure with a single hole charge of 24 kg; the buffer holes utilized an equally spaced air-spaced discontinuous decoupling charge structure with a single hole charge of 14 kg, forming an effective buffer zone between the main blasting area and the presplitting surface. The detonation sequence involved presplitting holes detonating first, followed by main blasting holes, and then buffer holes detonating last. This achieved a construction breakthrough with a maximum single cycle footage of 10m and a single blasting volume of 1377 m³. Field monitoring data shows that this system effectively controls blasting vibration velocity within 8.2 cm/s, with an average over-excavation of 8.6 cm and a half-hole rate of 91.8%, forming an underground tunnel blasting construction method with significant engineering characteristics.