Abstract:
From an engineering perspective, pumice particles are problematic because of their crushability and compressibility, which can be attributed to their vesicular nature. Currently, information on the geotechnical characteristics of pumice sands is limited. While extensive empirical and laboratory tests have been implemented to characterise their behaviour, these approaches are generally time-consuming and expensive. These drawbacks have motivated research on the effects of particle breakage on the response of pumice sand specimens through discrete element method (DEM)-based numerical models, as an attempt to provide insights into the microscale and macroscale behaviour of pumice sand as crushable granular materials. Hence, in this study, a series of single-particle crushing tests and DEM simulations were conducted on highly crushable pumice sand particles to evaluate their crushing behaviour. Herein, the DEM model was modified to consider the crushability of the simulated particles. For the particle crushing criteria, a linear elastic formulation was used, which considered the effect of the size and of the material properties (such as intrinsic strength, microstructure parameter, and compressive strength) of each particle. Note that the breakage criteria do not only apply to the highest particulate force; there is also a strong built-in dependency on the characteristics of particles in contact. Once the specified limit condition for particle crushing is reached (when intrinsic strength is greater than mobilised strength), a particle will split into smaller, inscribed tangent spheres.
Three-dimensional DEM models were developed using the open-source code YADE to simulate the behaviour of crushable pumice sand under both static and dynamic loading conditions, and the microscale crushing mechanisms of pumice were numerically investigated. Special focus was given to the particle-scale mechanisms that are dominant in conventional geotechnical laboratory-scale experiments, including 1D compression and drained, undrained and cyclic triaxial tests, on
crushable granular particles. The mechanism and effect of particle crushing during cyclic loading and the corresponding improvement in liquefaction resistance were also elucidated through the DEM models. The results showed that particle crushing was essential for realistically capturing the behaviour of pumice sand, and the inherent capabilities of DEM were used to gain insights into the effects of different conditions on the degree of crushing. Thus, this study provided a better understanding that can ensure proper material characterisation of highly crushable particles, which can be used to improve current approaches in assessing their mechanical behaviour.