Abstract: To investigate the macro- and meso-mechanical evolution of pebble-soil mixtures, we developed a Python-based random generation algorithm through ABAQUS secondary development, creating morphologically representative models of natural pebbles. Through triaxial compression numerical simulation tests, the influences of characteristic parameters such as pebble content, distribution inclination angle and roundness on the macroscopic and microscopic deformation and failure forms of pebble-soil mixtures were analyzed, and the variation laws of key mechanical parameters were revealed. By integrating 3D digital image correlation (3D-DIC) technology, we tracked real-time surface and internal deformation during laboratory testing, thereby validating the rationality of numerical simulation results. Fracture propagation exhibits pebble-content-dependent characteristics: low-content specimens predominantly show “unilateral flow around with rock penetration” and “envelopment with rock penetration”, whereas high-content specimens demonstrate “single rock rotation” and “strike-slip” mechanisms. Increasing pebble content drove shear zone evolution through three distinct phases: initial smooth planes progresses to X-shaped configurations, ultimately developing arc-network structures. Force chain networks transition from diffuse X-cross patterns to well-defined vertical orientations with increasing directional alignment. With the increase of pebble content and the improvement of roundness, the compressive strength, internal friction angle and cohesion of the specimens show an increasing trend; as the pebble inclination angle increases, the compressive strength, internal friction angle and cohesion show a decreasing trend. DIC-recorded uniaxial compression tests confirm congruence between experimental observations and numerical simulations across all pebble concentrations, particularly in surface crack initiation, propagation, and internal failure patterns. Our findings advance the mechanistic understanding of pebble-soil composites and establish a theoretical framework guiding future geotechnical applications involving these materials.

Key words: pebble-soil mixtures, random generation, ABAQUS secondary development, 3D-DIC technology, mechanical property