Research on the Application of New Comprehensive Construction Technology for Cast-in-place Piles in Deep Rockfill and Sand Layers

To address the challenges of difficult hole formation, borehole wall instability, low efficiency, and high costs in the construction of rotary drilling cast-in-place piles in complex strata where a deep rockfill layer and an underlying sand layer coexist, this paper proposes a combined construction technique integrating a "high-power rotary drilling rig + long casing" for penetrating the rockfill layer and a "conventional rotary drilling rig + special slurry" for drilling in the sand layer. Taking 546 cast-in-place piles in a seaside construction project in Huizhou, Guangdong Province as an example, the key construction technologies, pile quality, and economic analysis are detailed. Test results show that Class I piles account for 97.7%, with no Class III or IV piles; the vertical compressive bearing capacity of single piles meets the design requirements, with a maximum settlement of only 6.05 mm~15.23 mm. Compared with the traditional full-rotation full-casing technique, this process improves construction efficiency by 20%~30% and reduces overall cost by 15%~20%. This technology provides an efficient, economical, and reliable solution for the construction of cast-in-place piles in areas with deep rockfill and sand layers.