UCSD1: 3D Nonlinear Hysteretic Soil Model

UCSD1 userdefined model (UDM) is an elasticplastic material in which plasticity exhibits only in the deviatoric stressstrain response (Elgamal et al. 2008)*. The volumetric stressstrain response is linearelastic and is independent of the deviatoric response. 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, organic soils or clay under fast (undrained) loading conditions.
For questions or remarks, please send email to Dr. Ahmed Elgamal (elgamal@ucsd.edu) and Dr. Jinchi Lu (jinlu@ucsd.edu).
*Elgamal, A., L. Yan, Z. Yang and J. P. Conte. (2008). "ThreeDimensional Seismic response of Bridge FoundationGround System," Journal of Structural Engineering, ASCE, Vol. 134, No. 7, 11651176.
UCSD1 Soil Model .DLL Files
There are 3 versions available (1D shearbeam, 2D and 3D versions). Please download a corresponding .dll file below and place it in the "exe32\plugins\models" folder under FLAC/FLAC3D installation directory (e.g., usually at "C:\Program Files (x86)\Itasca\FLAC700" for a 32bit version of FLAC 7).1) 1D Shearbeam Version:
This version allows for onedimensional (1D) site response analysis in FLAC. No limit for the number of yield surfaces.
File: ucsd1demo.dll Download for FLAC 7(Coming soon!) Download for FLAC 8(Coming soon!)
Command to load the model in FLAC 7/FLAC 8: model dll ucsd1demo
Example File (230 MB): UCSD1_Example.rrr
2) 2D Version:
This version allows for twodimensional (2D) analysis in FLAC. A dongle is necessary to operate the full version. Without a dongle, the number of yield surfaces is limited to 3.
File: ucsd1.dll Download for FLAC 7(Coming soon!) Download for FLAC 8(Coming soon!)
Command to load the model in FLAC 7/FLAC 8: model dll ucsd1
Click here for an example (Coming soon!)
3) 3D Version:
This version allows for threedimensional (3D) analysis in FLAC3D. A dongle is also necessary to operate the full version. Without a dongle, the number of yield surfaces is limited to 3.
File: ucsd1.dll Download for FLAC3D 5 (Coming soon!)
Command to load the model in FLAC3D: model ucsd1
Click here for an example (Coming soon!)
Model Parameters
In the UCSD1 soil model, the shear stressstrain backbone curve is represented by the hyperbolic relationship, if a modulus reduction curve is not provided.1) Hyperbolic Relationship for Stressstrain Backbone Curve
If a modulus reduction curve (G/Gmax) is not provided, the hyperbolic curve will be used. The syntax to use this soil model in FLAC/FLAC3D is as follows:
prop shearModul ... poissonRatio ... shearStrength ... peakShearStra ... &
noYieldSurf ...
in which:

shearModul  Lowstrain shear modulus (G).
poissonRatio  Poisson's ratio.
shearStrength  Shear strength (τ_{f}).
peakShearStra  The shear strain at which the shear strength shearStrength is reached (γ_{max}).
noYieldSurf  Number of yield surfaces (1 or larger).
Parameters  Soft Clay  Medium Clay  Stiff Clay 
shearModul  1.3e+07 Pa  6.0e+07 Pa  1.5e+08 Pa 
poissonRatio  0.4  0.4  0.4 
shearStrength  18,000 Pa  37,000 Pa  75,000 Pa 
peakShearStra  0.1  0.1  0.1 
2) Userdefined Backbone Curve
If a modulus reduction curve is provided:
prop shearModul ... poissonRatio ... grTab ...
in which:

grTab  Table # for userdefined modulus reduction curve (G/Gmax). A separate FLAC/FLAC3D command table is needed to define the modulus reduction curve. In this case, the number of the points specified will be used as the Number of yield surfaces (Note: Please plot your own shear stressstrain curve based on the modulus reduction curve specified and make sure the modulus reduction curve you're using is reasonable).
Click here for some sample modulus reduction curves.
Model Performance
Below are some sample shear stressstrain response output of the UCSD1 model in FLAC (vertical axis: shear stress in Pa; horizontal axis: shear strain; Number of yield surfaces = 20): 
