Research on the Application of Collaborative Construction with Millisecond Delay and Smooth Blasting in Conglomerate Subgrade

In response to multiple technical challenges faced during the excavation of moderately weathered conglomerate subgrade in the MLTJ-1 section of the Mianxi Expressway, including proximity to sensitive structures, traversing mined-out areas, and forming high-steep slopes, this paper proposes a collaborative construction method combining "medium-deep hole bench millisecond blasting and slope smooth blasting." Based on the anisotropic characteristics of conglomerate and environmental constraints, a closed-loop control procedure of "geological confirmation—parameter optimization—effect feedback" was established through field trial blasts, theoretical calculations, and parameter optimization. High-precision millisecond initiation was achieved using digital electronic detonators, with optimized hole pattern layouts, charge structures, and initiation sequences, along with targeted treatment measures for special geological sections. The project implementation covered a blasting volume of 600000 m³, with an average daily efficiency of 2,800 m³/d. The results indicated that the blasting vibration velocity was controlled within 1.0 cm/s, the flying rock distance was ≤105 m, the slope half-hole ratio was ≥90%, over-excavation was reduced by 33.3%, and the cost of secondary rock breaking was decreased by 16.8%. The research findings verify that this collaborative blasting technology offers safety, efficiency, and cost-effectiveness in complex environments, providing a quantifiable and replicable technical pathway for blasting operations in similar conglomerate strata for expressway subgrades.