Deformation of Compressible Layers Below Pile Foundations of a High-Speed Railway

New installation methods and techniques using single-point settlement gauges to monitor the compression deformations of pile shafts and soil layers below the pile bottom were developed. A field study was conducted at a test site of the Beijing–Shanghai high-speed railway, and a 3D finite-element analysis was performed to analyze the deformation behavior of the pile foundation. The measured compression deformations of the pile shafts from the single-point settlement gauges agreed well with the values obtained from the strain gauges, which validated the effectiveness and feasibility of the developed methods and techniques. During the construction of the high-speed railway, the pile top settlement–time curve presented a ‘ladder’ shape and then increased with time before gradually stabilizing. The compression deformations of the subsoil layers within 20–30 m below the pile bottom were not significantly different, and the average unit compression deformation under 20 m below the pile bottom remained approximately constant after construction. The axial force and tip resistance of the pile shaft increased during the consolidation of the soils surrounding the pile shaft and might result in an increase of the compressions of the pile shaft and subsoil layers. The thicknesses of compressible layers (hc) of the tested pile foundations were determined using a deformation ratio method and were approximately 15.0 m. These results demonstrate that the developed methods and techniques are useful for studying the compression deformations of subsoils below the pile bottom (especially for super-long piles).