Key Construction Technologies for Super-thick New Backfill Layer Deep Cast-in-place Piles

The ultra-thick recent backfill layer, due to its complex composition, loose structure, and poor compactness, is prone to risks such as rapid slurry leakage, cross-hole flow, and hole collapse during pile foundation construction, leading to difficulties in controlling sediment thickness and quality issues such as drill burial and reinforcement cage burial. To improve the quality of borehole formation and pile construction efficiency under such geological conditions, this study takes a airport pile foundation project as a case study. Based on construction practices and literature research, it systematically analyzes the challenges of borehole formation in thick backfill layers and structural fracture zones using rotary drilling cast-in-place piles. A comprehensive technical system guided by the principle of "prevention + in-process control, with prevention as the priority" is proposed. By increasing the slurry density, optimizing viscosity, and incorporating a secondary air compressor for hole cleaning, slurry leakage was significantly reduced, effectively maintaining hole wall stability. Comprehensive measures such as embedding long casings, graded leak stoppage and backfilling, low-grade plain concrete backfilling with static placement, and optimized construction organization were implemented. These measures significantly reduced the frequency of slurry leakage per pile, shortened the construction cycle by approximately 50%, and achieved a proportion of 95.45% for Class I piles. The results verify the adaptability and effectiveness of this technical system in controlling pile quality, providing a reference for similar pile foundation projects in complex, thick recent backfill strata.