Geotechnical properties of a pumice sand

The pumice sand found in the North Island of New Zealand has properties which lie beyond those usually associated with cohesionless soils. The grains are very soft and the sand has a high void ratio, thus forming a compressible material. This paper presents the results of a series of drained triaxial and K-0 tests on dry pumice sand. The tests were conducted to evaluate the geotechnical properties, particularly the critical state parameters, of the sand and also to provide background information for interpretation of cone penetration tests in the material. The K-0 tests were used to evaluate the compression envelope under conditions of no lateral strain and to determine values of constrained modulus. Significant grain crushing was found to occur during testing even at low confining stress, in fact the stress-strain-strength behaviour of the material is dominated by particle crushing. Routine soil testing techniques were found to be inadequate for the evaluation of the specific gravity of pumice sand particles and a different technique was used for this purpose. The angle of friction of pumice sand was found to be larger than that of quartz sands, however pumice sand required very large shear strains to mobilise the peak and critical state shear strength and, for several tests, critical state conditions were not reached.