Prediction of creep strain time history from time history of stress relaxation of sand based on triaxial compression tests

Most geotechnical engineering materials exhibit behaviours responded to the loading rate effect, which are due to their viscous property, e.g., creep (CP) by sustained loading, stress relaxation (SR) by keeping the strain constant, stress jump upon a stepwise change in the strain rate, etc. Precise prediction of creep strain is important for evaluation of the long-term performance of a soil structure under a constant working load. This research performed a series of special drained triaxial compression tests on a sand type. This sand was processed and treated in King Mongkut’s University of Technology Thonburi (KMUTT), and hence it was named KMUTT sand. Various loading histories were applied so as to evaluate viscosity type and investigate the CP and SR behaviours at various values of stress ratio. An analytical framework was developed from systematic relationships between the elapsed times necessary to reach the same irreversible strain rate in CP and SR tests and those between the irreversible strain increments necessary to reach the same irreversible strain rate in CP and SR tests. The followings are found. KMUTT sand exhibits the behaviours responded to the loading rate effect by which the viscosity type is TESRA (Temporary or Transient Effects of Strain Rate and Strain Acceleration) in the pre-peak regime translated to P&N (Positive & Negative) in the post-peak regime. Time history of CP can be precisely predicted by time history of SR performed for a much shorter time. And, time factor from the prediction increases with increasing stress ratio.