Undrained Cyclic Behavior of Reconstituted Natural Pumiceous Sands

Abstract

Sands containing pumice particles are widely distributed over the Waikato Basin, North Island in New Zealand. These pumiceous sands, due to the vesicular nature and presence of internal voids in the particles, are highly crushable, compressible, and lightweight; factors which make them problematic from an engineering point of view. In this paper, in order to investigate the effect of particle shape and crushing on the undrained cyclic behavior of natural pumiceous sands, we report the results of undrained cyclic triaxial tests performed on natural pumiceous sand and Toyoura sand with different relative densities. The test results illustrate that natural pumiceous sands show significantly different cyclic behavior when compared with Toyoura sand. For instance, during the cyclic triaxial test, pumiceous sands start to deform from the start of the cyclic loading, and the axial strain gradually increases until 5% double amplitude axial strain is reached. In contrast, Toyoura sand undergoes a significant number of cycles with negligible deformation, followed by a sudden increase in deformation in a few cycles, to reach 5% double amplitude axial strain. In addition, pumiceous sands initially show a very contractive behavior under the application of cyclic loading, but after a few more cycles, this changes to a very strong dilative behavior. Due to the formation of a stable soil skeleton inside the pumiceous specimens, instability is not observed and the liquefaction resistance of pumiceous sands is considerably higher than that of Toyoura sand under the same relative density.