Smooth Nonlinear Hysteresis Model for Coupled Biaxial Soil-Pipe Interaction in Sandy Soils

AbstractPipelines as infrastructure components are very vulnerable to geohazard-induced ground deformation and failure. Soil–pipe interaction (SPI) thus is very important for the assessment and design of resilient pipeline systems. Previous work on SPI modeling has been based on crude assumptions, such as representation of the soil as uncoupled three-dimensional bilinear springs, and quasi-static loading conditions. This paper proposes a simplified macroelement designed to capture the effects of dynamic SPI in cohesionless soils subjected to arbitrary loading normal to the pipeline axis. First, we present the development of a uniaxial hysteresis model that can capture the smooth nonlinear reaction force-relative displacement curves (FDCs) of SPI problems. Using the unscented Kalman filter, we derived the model parameter κ that controls the smoothness of transition zone from linear to plastic using published empirical and experimental data. We extended this uniaxial model to biaxial loading effects, and showed that the macroelement can capture effects such as pinching and shear–dilation coupling. The model input parameters were calibrated using finite-element (FE) analyses validated by experiments. The FDCs of the biaxial model were verified by comparison with FE and smoothed-particle hydrodynamic (SPH) simulations for different loading patterns: cyclic uniaxial, 0-shaped, 8-shaped, and transient loading. Accounting for smooth nonlinearity, hysteresis, pinching, and coupling effects, the proposed biaxial macroelement showed good agreement with FE and SPH analyses, while maintaining the computational efficiency and simplicity of beam on nonlinear Winkler foundation models, as well as a small number of input parameters.