Stress Transfer and Settlement of a Rail-Guided Derrick Foundation on Layered Fill–Residual Soil: A Field Case Study

The stress transfer and settlement behaviour of rail-guided derrick foundations on layered fill–residual soil remain insufficiently characterised by field measurements. This study combines approximately 260 days of field monitoring at the Jiaoye 14# shale gas pad in Chongqing, China, with a Winkler–Flamant analytical model and a three-dimensional finite-element (FE) model. Thirty earth pressure cells were installed at shallow and deep levels. Synchronous stress increments were used to evaluate stress transfer between the two monitoring levels, while a separately defined deep-gauge stress difference was used for analytical load back-analysis. The analytical equivalent load ranges from 4.01 to 4.36 MN for the adopted subgrade reaction moduli and a 12 m loaded length. For a synchronous loading event on 15–17 December 2025, the FE-predicted and measured deep-to-shallow stress-increment ratios were 0.884 and 0.783, respectively, indicating reasonably comparable stress-transfer responses. At a common reference load of 4.2 MN, the analytical and FE soil compressions are 19.47 and 12.22 mm, respectively, with the residual soil contributing approximately 94–95% in both calculations. The measured cumulative settlement of 45.8 mm reflects a different loading history and observation location and therefore cannot directly validate these static estimates. The results demonstrate the value of combining field monitoring, analytical load back-analysis and three-dimensional FE modelling to interpret stress transfer and identify the principal compressible layer beneath rail-guided derrick foundations.