Portable Rock-Analog Deformation Apparatus (PRADA)


The Portable Rock-Analog Deformation Apparatus (PRADA) is a simple device designed for making precise rheological measurements of relatively soft materials such as waxes or clays. Many of these materials exhibit non-linear rheologies, and are thus suitable analogs for rocks deforming at high pressure and temperature. A prototype of this apparatus was built in 2009, and has been incorporated successfully into Washington University’s undergraduate curriculum through structural geology and introductory geophysics classes.

An award from NSF (EAR-1352306) supported the design and construction of 12 of these apparatuses (Figure 1). These apparatuses were distributed free of charge to liberals arts colleges and other institutions to help build an infrastructure for teaching experimental rock mechanics at the undergraduate level.  If you are interested in using a PRADA for your class, please contact Phil Skemer (pskemer@wustl.edu) for more information.

The PRADA is an example of what is known as a “dead-weight creep apparatus,” which means that near-constant stresses are applied using calibrated weights. Differential stresses, which drive deformation, are calculated easily from the forces being applied and the dimensions of the test specimen.   Displacement (and thus strain) is calculated using a precise digital indicator. The apparatus is designed so that it can be constructed and maintained with minimal equipment.   All parts are obtainable from the supply catalog McMaster-Carr (www.mcmaster.com). All PRADAs come with a lifetime service contract.

Where are the PRADAS?  If you build your own let Phil know so that you can be added to our list!

  • Washington University in St Louis
  • Pomona College (Linda Reinen)
  • Lakehead University (Mary Louise Hill)
  • McGill University (Christie Rowe)
  • Salem State University (Sara Mana)
  • University of Oklahoma (Brett Carpenter)
  • Sonoma State University (Matty Mookerjee)
  • University of Louisiana, Lafayette (Raphael Gottardi)
  • UMass Amherst (Michele Cooke)
  • San Jose State University (Kim Blisniuk)
  • Oklahoma State University (Daniel Lao-Davila)
  • University of Toronto, Mississauga Campus (Sheila Ballantyne)
  • Rice University (Melodie French)

PRADA Diagram

PRADA Parts List

PRADA User Manual

Logging Program for PRADA apparatus

SGT PRADA lecture

SGT PRADA rheology tutorial