Mechanical Behavior of Sand–Fly Ash Mixtures for Weak Rock Modeling

Abstract

This study investigates the mechanical behavior of artificial materials designed to replicate weak surrounding rocks for geo-mechanical model testing. Unlike previous studies that emphasized the ratio of fine to coarse aggregates, this research explores mixtures of sand (as coarse aggregate) and fly ash (as fine aggregate) combined with gypsum–water paste as the binder, with iron powder selectively introduced to regulate density. Cylindrical specimens of varying sand–fly ash ratios were prepared and tested under uniaxial compression. Results indicate that increasing fly ash content enhances density and stiffness due to pore filling between sand grains, while the gypsum–water binder provides a brittle yet cementitious cohesion suitable for simulating weak rock mass behavior. Iron powder addition effectively increased bulk density without significantly altering frictional properties. Stress–strain behavior revealed a transition from low-strength brittle failure at lower fly ash content to more ductile and stable responses at higher fly ash proportions. Numerical simulations (discrete element method) captured micro-mechanical trends such as particle contact forces and crack propagation, which agreed with experimental observations. These findings demonstrate that sand–fly ash mixtures bounded with gypsum paste offer a practical method for simulating weak surrounding rocks in physical model studies, providing an alternative to traditional cement-based formulations.