Simplified analysis of adjacent single-pile response subjected to foundation pit excavation based on virtual image technique

Foundation pit excavation can produce additional deformation and internal forces on the adjacent piles of buildings, and it will reduce their bearing capacity. This will threaten the security of the upper structure if the deformation of piles is too large. To avoid the drawbacks of three-dimensional numerical analysis, such as complexity modeling and time consuming, and to take full use of foundation pit supporting displacements provided by the in-situ monitoring technique, a two-stage method based on virtual image technique is presented for determining the behavior of adjacent single-pile induced by foundation pit excavation. An improved calculation model, Kerr foundation model, is proposed, which makes up for the defects that Winkler foundation model cannot consider the continuity of soil. The virtual image technique is used to estimate the free-field soil displacements induced by excavation in the first stage. The foundation pit supporting displacements are employed to calculate the free-field soil displacements. In the second stage, the free-field soil displacements are applied to the piles, the displacement governing equations of piles are established based on Winkler and Kerr foundation models, respectively. The simplified formula for pile response induced by excavation is obtained, including horizontal displacements, bending moments, and shearing force. The results are compared with that from existing calculated results, measured data, and 3D FEM. Good agreements are obtained. The simplified solution based on the Kerr foundation model is more accurate than the solution of Winkler foundation model. It indicates that the simplified calculation method can provide a theoretical base to analyze the impacts of excavation on the adjacent piles effectively.