Rate-dependent behaviour of undisturbed gravelly soil

A series of drained triaxial compression tests was performed to evaluate the rate-dependent stress-strain behaviour of large- and medium-size undisturbed gravelly soil samples (UGSSs). A newly developed sampling method, using thick water-soluble polymer solutions, was employed for retrieving the samples from three tunnel excavation sites in Toyama Prefecture, Japan. To evaluate the rate-dependent stress-strain behaviour, the loading rate was changed stepwise many times and drained sustained loading was performed at prescribed stress states during otherwise monotonic loading at a constant vertical strain rate in the tests. The UGSSs from natural deposits at two of the sites exhibited Isotach-type viscous properties. For the UGSS retrieved from the site improved by chemical injection prior to the start of the excavation, the type of viscous property changed from Isotach to P&N with strain. A comparison between the values of the viscous parameters of reconstituted granular materials evaluated in previous studies and those of these UGSSs was discussed. Test results from drained unconfined compression tests were also presented to investigate the cementation of UGSSs.