Abstract: 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.