Constant Rate of Strain (CRS)

The Constant Rate of Strain (CRS) test is used to estimate the consolidation parameters of fine-grained soils. The CRS-test differs from standard consolidation tests as it offers a continuous rate of strain and continuous recording of the consolidation pressure. Furthermore, it is possible to execute an un- and reloading stage and/or relaxation stage (with a constant height). Standard ‘Koppejan’ parameters are, however, not able to be determined using a CRS-device.

The following loading-scheme is suggested for a standard CRS-test:

1. Initial (low) vertical pressure around two kPa.

2. Loading up to four σ’vi.

3. Unloading down to two σ’vi.

4. Re-loading up to six σ’vi..

5. To determine the creep parameters a relaxation stage is necessary. This entails keeping the sample height constant whilst recording the change in vertical pressure. Normally the relaxation stage takes around 16 hours.

6. Loading up to  10 - 16 σ’vi. Samples with low initial pressures are loaded up to the highest value.

Geolab Wiertsema has six Constant Rate of Strain devices set up in a conditioned part of the  laboratory in Tolbert, The Netherlands.