As the soft soil in the Pearl River Delta area is deep, 50cm diameter cement mixing pile composite foundation is often used for road engineering.A municipal road in Hongwan District of Zhuhai adopts a mixing pile with a diameter of 80cm and a length of 27 m, which brings great difficulty to the construction of the project.In order to ensure the engineering quality, the bit optimization scheme was adopted to improve the blades from the conventional two layer and four groups of blades to three layer and six groups of blades. The projection direction of each layer of blades was vertical, which could increase the mixing times and improve the mixing uniformity.At the same time, double-channel teeth were added to effectively increase the smoothness of slurry flow.The optimized nozzle is improved from a nozzle located at the bottom of the drill bit to the left and right sides of the bottom of the drill pipe to effectively relieve the blockage of the nozzle and silt backflow and other problems.Optimize the grouting pressure. The grouting pressure is generally 0.4-0.6 MPa. After optimization, the upper limit of 0.6 MPa is used in the first stirring and spraying process, and 0.4 MPa is used in the second stirring and spraying process.The advantage is that in the first time of mixing, excess cement grout is ejected for mixing, and in the second time, the total grout dosage can be controlled by reducing the grouting pressure, which effectively improves the quality of pile body and controls the cost.Improve the drilling speed of drill pipe, accelerate the speed when sinking, slow down the speed when lifting, to ensure uniform soil mixing.Through the above measures, the strength of the mixing pile body is improved and the integrity of the pile body is guaranteed.Pile integrity, effective pile diameter, pile length, pile strength uniform accord with the design.The difficult problem of large diameter and deep cement mixing pile is solved, which provides a good reference value for similar engineering.