Shear Behavior and Failure Mechanism of a Nodular Pile–Cemented Soil Interface: A Numerical Study Considering the Evolution of Overall and Local Microstructures

With the continuous development of marine resources, the demand for foundation bearing capacity in marine and coastal engineering projects has been increasing, leading to the widespread application of composite piles in marine geotechnical engineering. In this study, a series of three-dimensional nodular pile–cemented soil interface shear tests based on static drill–rooted nodular (SDRN) piles were conducted, taking into account the nodular pile node angle and cemented soil strength. The test results demonstrate that a larger nodular pile node angle weakens the interlocking effect between nodular pile and cemented soil, while the cemented soil strength not only significantly increases the interface shear resistance but also improves the interface deformation capacity. To further investigate the load transfer mechanism of SDRN piles from a microscopic perspective, a numerical model was established using the discrete-element method–finite difference method (DEM-FDM) coupling method. After verifying the validity of the DEM-FDM model in terms of mechanics and failure modes, sensitivity analyses were conducted on the interface friction coefficient, interface bond strength, and loading velocity. Finally, the overall and local microstructural evolution of cemented soil during the shear process was investigated. These findings can provide valuable insights for an analysis of nodular pile–cemented soil interface mechanical behavior and the application in engineering projects of the SDRN pile.