Theoretical method for additional horizontal stress of isolation piles due to adjacent loading

Isolation piles are widely used to increase the horizontal resistance of high‐speed railway under adjacent loading in soft soils. This study proposes a theoretical model for horizontal additional stress of pile‐reinforced area subjected to adjacent loading. The isolation piles and the soil between piles in the reinforcement area are equivalent to a uniform medium in the proposed model. The Heaviside function is introduced to avoid the partition solution problem of pile‐reinforced area and the foundation soils. A combined method with the inverse Fourier transform, Gauss integral, Lagrange quadratic interpolation, and Simpson quadrature formula is employed in the calculation process. The theoretical model is validated by the finite element method. According to the calculated results, the distribution of horizontal additional stress is obtained. The horizontal soil displacements at the location of the railway increases in the depth range of 0–2.5 m and then gradually decreases. The proposed model with engineering significance is available for preliminary design of isolation piles.