Structure feature and compressive crushing behavior of lightweight clay aggregate particle: experiments and numerical simulations

Lightweight expanded clay aggregate (LECA) is a lightweight granular material, which can be used as an ideal backfilling geomaterial attributed to its porous particles. Through X-ray tomography images, it is found that LECA particle is a porous composite particle with a strong shell and a fragile core, originating from the sintering process of LECA production. Uniaxial compression experiments and discrete element method (DEM) simulations of uniaxial, biaxial and embedded multi-point (EMP) compressions were performed to study the crushing behavior of LECA particles. It is found that DEM simulation can well reproduce the structure and crushing behavior of LECA particles. Particularly, the EMP compression mimicked realistic working status of crushable particles in a stressed granular assembly, and the diverse changes of contact numbers, locations and force magnitudes were replicated in EMP compression. The experiment and simulation results exhibit large scattering in compressive crushing responses, and such variability has inter-particle and intra-particle sources. The size scaling law of crushing strength for the porous LECA particle does not obey the Weibull model prediction which was originally developed for solid particles. A significant variation of Weibull modulus with particle size was observed, attributed to the strong shell and fragile core structure features. The compressive strength would drop with increased lateral constraints, which is opposite to previous observations in the literature and is attributed to the unique stress distribution within LECA particle. Finally, a unified description of particle compressive strength following Weibull distribution is proposed and the experimentally available uniaxial compressive strength law becomes a special case. Particle size effects on uniaxial compressive strength and coordination number effects on Weibull modulus need to be carefully considered.