Experimental study on the influence of fine particle content on the compression characteristics of filling granular materials

The compressional behaviour of backfill soils is critical for assessing the stability of reclaimed ground. This study investigates the influence of fine particle content on the compressibility of mixed granular fill materials. A series of tests were conducted using a self-developed lateral confinement device, systematically evaluating the compression characteristics of mixed fills with fine contents. The results indicate that the compressibility of the mixed fill increases with higher fine particle content. During compression, the compressive modulus of mixtures with varying fine contents exhibits a three-stage evolution – hardening, softening and re-hardening – directly mirroring the micro-scale process of force chain restructuring, collapse and reformation within the fill. Fines act as a ‘lubricant’, reducing the stability of the coarse skeleton, with the most pronounced impact occurring during the softening stage. At 35% fine content, the compressive modulus dropped by more than 70 MPa in this stage. Furthermore, the lateral pressure coefficient exhibits a nonlinear decay with increasing vertical stress. The lateral pressure coefficient increases with fines content, leading to differences of up to 0.1 under identical stress conditions across mixtures with different fines contents. These findings provide direct guidance for the design and stability evaluation of backfill structures.