Settlement and bearing capacity of single pile based on shear characteristics of pile-soil interface

In recent years, the northwest region has seen an increase in high embankment sites, leading to widespread use of pile foundations to mitigate uneven settlement of building foundations. However, in loess embankment sites, single piles experience significant deformation in the surrounding soil after loading, complicating the settlement mechanism of such single piles. As pile head settlement calculation is crucial for pile foundation design, this paper establishes a calculation model for pile head settlement of single piles in high embankment loess sites. The proposed model considers the interaction between piles and soil at the pile-soil interface and the shear deformation of the soil in the shear zone outside the pile-soil interface, based on the traditional load transfer method and shear displacement method. It classifies single pile types into friction piles and end-bearing friction piles based on the pile end boundary and establishes differential equations for pile body displacement control in both the elastic and plastic phases of the surrounding soil. Solving these equations with boundary conditions yields pile body displacement, axial force, and lateral friction resistance. Additionally, the model calculates the shear deformation of the soil in the pile-soil interface zone using elastoplastic theory and determines the total settlement at the pile head using the superposition principle. The ratio of pile length to the plastic development depth of the surrounding soil is defined as the pile bearing capacity safety factor, denoted as K. Results from case studies and comparisons with field test data demonstrate that the pile head total settlement calculated using the model proposed in this paper aligns closely with the field test results. When the pile head load is relatively small and the surrounding soil is in the elastic phase, the influences of the pile end boundary on pile body axial force, displacement, and lateral friction resistance are minimal. However, as the surrounding soil enters the plastic slip phase, the effect of the pile end boundary becomes more significant, and considering the bearing capacity of the pile end soil greatly enhances the ultimate bearing capacity of the single pile. This paper establishes a comprehensive calculation model that combines the load transfer method and the shear displacement method. It not only accounts for the relative slip at the pile-soil interface but also calculates the shear deformation of the soil in the zone outside the pile-soil interface. This leads to a more accurate calculation of the pile head total settlement and provides valuable insights for the analysis and control of single pile settlements in similar sites.