<p>This study presents a new approach for estimating the relative density (D_R) of sand using particle configuration parameters from soil images. Focus was on utilizing soil assembly images depicting particles in group configuration. Soil images at various D_R were prepared and adopted to analyze the assembly and shape configurations. The values of particle diameter (d), perimeter (p) and total perimeter (p_tot) obtained from soil assembly images at different D_R were evaluated and compared with those of individual bulk particles. As D_R increased, d and p decreased, while p_tot remained similar. The sphericity (S) and roundness (R) of soil assemblies in group configuration were evaluated. It was found that S was smaller than for bulk particles, whereas R was similar. The number of particles (NoP) from soil assembly images was newly introduced as an indicator to volume characteristics. Through the correlation analysis, a close relationship of D_R, p_tot and NoP was found, where p_tot increased linearly with NoP. Based on this finding, a unified correlation model utilizing combined parameters of p_tot and NoP was established for estimating D_R. Verification tests were additionally conducted using different types of sands, confirmed the validity and efficacy of the proposed image-based D_R estimation method.</p>