Strain Rate and Stress Relaxation Effects on Pressuremeter Testing in Clays
Abstract
This research was undertaken to answer issues related to cavity expansion and in-situ testing using the pressuremeter. Emphasis of the research was placed upon validating the fundamental concepts underlying the cylindrical cavity expansion theory. Test were performed in a cuboidal shear device (CSD) at strain rates of 0.01%, 0.05%, 0.10%, 0.50%, 1.00% and 5.00% per minute on artificially sedimented specimens of kaolin clay and a kaolin-ground silica mixture with a plasticity index in the range similar to most clays. It was found from the experiments that the normalized shear strength (with respect to 0.01%/min) increases linearly with the logarithm of strain rate. The increase in undrained shear strength in the pressuremeter stress path is about 14.3% per log cycle for kaolin clay and 15-3% for the kaolin-silica mixture. The undrained shear strength in the conventional triaxial test was found to increase about 8 to 10% for a tenfold increase in strain rate. Therefore, it can be concluded that the undrained shear strength increases about 40-50% more in pressuremeter stress path tests than in the triaxial stress path tests. A new state variable, indicative of the fabric of clays is introduced. Based on these concepts and a general failure criterion, a simple model to predict failure parameters of anisotropic clays for many commonly encountered stress paths was developed. The model capability to interpret in situ strength measured under a given stress path and transfer it to another stress path was illustrated. Finally, the ability to obtain failure parameters for any stress path using data from a single CIUC test was demonstrated.
Document Details
- Document Type
- Technical Report
- Publication Date
- Mar 01, 1992
- Accession Number
- ADA250335
Entities
People
- A. Skandarajah
- Dayakar Penumadu
- J. L. Chameau
Organizations
- Purdue University