Engineering property evaluation of soil before and after PHC pipe pile installation

Researchers at home and abroad are mainly focused on the bearing capacity, effects of soil plug and pile driving of PHC pipe piles. However, little attention is paid to property variation of soil before and after their installation especially when different installation technology is adopted. For further study of engineering property of PHC pipe pile composite foundation, the property variation of soils among PHC pile piles before and after their installation was studied with CPTU in-situ test technique in northern connection project of Chongqi Bridge expressway. The results indicate that, regardless of the pile installation, either hammer percussion method or static pressure method, several physical and mechanical parameters of soils among PHC piles were increased while both the consolidation coefficient and permeability coefficient of soft soil decreased one year after installation. For hammer percussion method, during the process of pile driving, soils around the pile accept a strong non-uniform drag effect, which makes the soil compacted in local area significantly. So the CPTU tip resistance of hammer percussion method is often significantly higher than that of static pressure method in local areas, which also leads to that the average deduced parameters of hammer percussion method such as the relative density and the effective internal friction angle of sand or undrained shear strength of cohesive soil are usually higher. Under the condition of same geology and design parameters, the skin friction of soils around pile in hammer percussion method is generally lower than that of static pressure method. This is of great significance for the PHC pipe pile which used as friction pile and for the bearing characteristic of PHC pipe pile composite foundation.