Micro-mechanical properties of crushable pumice sands

Pumice materials are problematic from engineering and construction viewpoints because of their lightweight, highly crushable and compressible nature. The mechanical properties of pumice sands at particle-size level were investigated to better understand their behaviour. X-ray computed tomography images showed internal and surface voids within the pumice particles. The surface characteristics of pumice were then compared with those of other hard-grained soils. Detailed investigation showed that pumice samples consist of different types of particles. Next, single-particle crushing tests were conducted and the results indicated that, under the same condition, the crushing strength of pumice increased with decreasing particle size, consistent with that observed in hard-grained soils; however, the crushing strength of pumice is one order of magnitude lower, highlighting its crushability. Finally, geotechnical laboratory tests such as cyclic undrained triaxial tests and bender element tests were performed on pumice sand specimens and the results were compared with those obtained from hard-grained silica sands. The results confirmed that the micro-level characteristics of the sand particles have a significant effect on their macro-level response.