Numerical simulation of breakage in geogrid-encased recycled aggregate columns with a coupled continuum-discrete method

Abstract

The breakage of recycled aggregates (RAs) significantly impacts the interaction and load transfer within the geogrid-encased RA column (GERAC). This study develops a continuum-discrete coupled model that accounts for the breakability, shapes, and size distribution of RAs to investigate their breakage behavior under unconfined compression. The breakage process, contact and fracture behavior, and relative breakage (Br) are analyzed, with orthogonal analysis and parametric studies conducted to explore the factors affecting the breakage behavior of GERAC. The numerical results show that RAs experience both singular and multiple shear and tension fractures along the column. After loading, the breakage distribution is radially uniform, but decreases with depth, with shear fractures occurring 71.68% more frequently than tension fractures. Stress concentration occurs at low strains due to the irregular shape of RAs. Bond contacts increase by 9.22% and Br increases by 3.92%. Bond strength (σ), column diameter (D), relative density (Dr), modulus of geogrid (Eg), and gradation significantly influence Br, while Dr and Eg significantly affect the unconfined compression strength (qu) according to the orthogonal results. σ is the most sensitive and significant factor, with a threshold value of 7e5 Pa for reducing Br. Larger RAs are more susceptible to breakage, and careful selection Dr and Eg of RAs improves both qu and unconfined compression modulus (Ec) of GERAC. Recommended parameter values are provided to guide design and practical applications. The study also discusses limitations and future research directions to further advance this technique.