Factors Affecting the Torsional Response of Deep Foundations

摘要

Deep foundations supporting skewed bridges and flyovers may need to resist torsional loads induced by seismic loading. To facilitate the serviceability and ultimate limit state design of a geometrically-variable deep foundation subjected to torsion in multi-layered soils, a software package, TorPILE, is developed using a finite difference model (FDM) framework. Simplified, pressure- and state-dependent nonlinear torsional load transfer models relating the unit torsional resistance to the magnitude of relative displacement are developed using available interface shear tests and torsional load test data. The soil-structure interface behavior is simulated using hyperbolic displacement-hardening model for granular and plastic fine-grained soils that exhibit a contractive response and a displacement-softening model for granular soils with dilatant response. The FDM methodology, as well as the proposed torsional load transfer models, is validated by comparing the torsional responses of deep foundations predicted by TorPILE with the centrifuge test data reported in the literature. Parametric studies investigating the role of various design parameters, including the dimensions of deep foundations and soil properties, are conducted.