UCSD Soil Models

The UCSD soil models UCSDSAND3 and UCSDCLAY are three-dimensional (3D) elasto-plastic material models for the simulation of cohesionless and cohesive soils, respectively. These models have been evolving over the past two decades with extensive calibration through numerous sources including downhole-array records, laboratory tests, shake-table and centrifuge experiments. These soil models have been available in OpenSees since the early 2000s.

The UCSD soil models have now been implemented into a number of analysis packages including FLAC/FLAC3D and LS-DYNA as user defined materials. Please click the corresponding item in the menu above for detailed information regarding implementation in the various numerical codes. For illustration purposes, one-dimensional (1D) site response analysis examples utilizing these soil models are provided on this website. If you have any question, please contact Prof. Ahmed Elgamal (E-mail: elgamal AT ucsd DOT edu).

UCSDSAND3 - Pressure Dependent Model

UCSDSAND3 material is a 3D elasto-plastic material model for simulating the essential response characteristics of pressure sensitive soil materials under general loading conditions. Such characteristics include dilatancy (shear-induced volume contraction or dilation) and non-flow liquefaction (cyclic mobility), typically exhibited in sands or silts during monotonic or cyclic loading.

In this model, plasticity is formulated based on the multi-surface (nested surfaces) concept, with a non-associative flow rule to reproduce dilatancy effect. The yield surfaces are of the Drucker-Prager type. This sand model reproduces conventional liquefaction triggering logic (Khosravifar et al. 2018)*. Please click here for more information.

*Khosravifar, A., A. Elgamal, J. Lu, and J. Li. (2018). "A 3D model for earthquake-induced liquefaction triggering and post-liquefaction response." Soil Dynamics and Earthquake Engineering, 110, 43-52.

UCSDCLAY - Pressure Independent Model

UCSDCLAY material is a 3D elasto-plastic material model which reproduces nonlinear hysteric shear behavior and accumulation of permanent shear deformation. Plasticity is exhibited only in the deviatoric stress-strain response (Elgamal et al. 2008)**. The volumetric stress-strain response is linear-elastic and independent of the deviatoric response. Nonlinear response is formulated based on the multi-surface (nested surfaces) concept, with an associative flow rule. The yield surfaces are of the von Mises type.

This material is implemented to simulate monotonic or cyclic response of materials whose shear behavior is insensitive to the confinement change. Such materials include, for example, clay under fast (undrained) loading conditions.

**Elgamal, A., L. Yan, Z. Yang and J. P. Conte. (2008). "Three-dimensional seismic response of Humboldt Bay bridge foundation-ground System," Journal of Structural Engineering, ASCE, 134(7), 1165-1176.