Bored piles of 600 and 1000mm diameter are designed for the Yantai Port Wanhua Industrial Park wharf upgrading project. The upper part is a thick layer of offshore backfilled stones, which is difficult to drill, prone to collapse, and difficult to form a hole. A large rotary drilling rig was used to drill the hole with the sim-casing process, where two layers of casing (inner and outer) were used to protective the wall. After drilling through the backfill layer and the mixed sand layer, the rotary drilling rig continued drilling with mud for wall protection, but the protection casing was no longer followed. In such a way, not only can the quality of the hole formation be ensured, but also the construction cost reduced. The outer casing can be pulled out after the completion of concreting and be re-used to reduce the project cost.