Background on PM4Sand

  • The sand plasticity model PM4Sand was developed for geotechnical earthquake engineering applications by Professors Ross W. Boulanger (homepage) and Katerina Ziotopoulou (homepage) at the University of California at Davis.
  • PM4Sand is a stress-ratio controlled, critical state-based, bounding surface plasticity model for sand (and other purely nonplastic granular soils) that has been implemented as a user-defined dynamic link library for use with the program FLAC and FLAC2D by Itasca (homepage). The model was developed and implemented to approximate stress-strain responses of specific importance to geotechnical earthquake engineering and liquefaction problems.
  • The companion model, PM4Silt (homepage), is available for modeling saturated, low-plasticity silts and clays that exhibit stress-history normalized behaviors.
  • The other tabs on this website provide access to the user manuals, dynamic link libraries, example files, and various reference sources.
  • We appreciate hearing from users, so please do send us an email (rwboulanger at or kziotopoulou at and let us know about your applications and experiences. 
Stress and strain graphs