A unified model embedding MCC-MLD constitutive laws in Biot’s framework for settlement of Weinan interbedded clay-sand loess foundations

Consolidation settlement prediction in interbedded clay–sand loess foundations is complicated by stratigraphic heterogeneity and hydromechanical coupling that homogeneous-soil models cannot capture. This study presents an integrated elastoplastic framework combining the Modified Cam-Clay model for loessial clay, the Wright–Duncan model for sand with particle breakage, and Biot’s consolidation theory in a unified implementation for the Weinan plain, China. Parameters for clay, sand, and transitional interlayers came from 20 borehole samples. Although each component is established, their integration with site-specific enhancements—a structure-dependent yield surface for shallow clay and a breakage-dependent hardening law for deep sand—constitutes a practical advancement. The numerical implementation via Python-Matlab, validated against borehole data from the same site using a reserved validation set (6 boreholes not used in calibration), reveals settlement in three stages—elastic rebound, primary consolidation (70–80% of total), and secondary creep—peaking at the 20–30 m clay–sand interface, where sand dilatancy transfers 12–18% of stress to clay, quantified by the proposed γ–μ interface parameter system. Spatially, settlement is shallow-dominated with deep-layer lag; temporally, sand accelerates clay pore-pressure dissipation by 35–40%. The model attains ± 5% accuracy versus ± 25% for homogenization and establishes a closed-loop monitoring–inversion–updating workflow. Assuming full saturation, it neglects matric-suction effects in the vadose zone, including water-table fluctuations and dry–wet cycles. At the Weinan site (water table 15–25 m), the model applies directly to deep saturated strata, contributing most (70–80%) of consolidation settlement; the shallow unsaturated zone requires caution and further characterization.