Experimental study on the permeability and mechanical properties of transparent sand at high relative density

This study address the limited understanding of the mechanical substitutability of transparent sand for natural sand under high-relative-density conditions. A transparent sand analogue was prepared using fused quartz sand (particle size: 1～3 mm) and a 60% calcium bromide solution as the pore fluid. At a relative density of 85%, a series of laboratory tests, including permeability, one-dimensional compression, direct shear and triaxial tests, were conducted to compare the mechanical behavior of transparent sand with that of saturated natural sand. The results indicate that the two materials exhibt comparable permeability coefficient, compression modulus, and shear strength parameters, falling within the same order of magnitude. The increase in pore fluid viscosity was found to slightly reduce permeability and strength, while exerting only a marginal influence on deformation characteristics and dilatancy behavior. A comprehensive evaluation demonstrates that the transparent sand system achieves a favorable balance between refractive index matching and mechanical similarity. Under the specified conditions, it can reliably replicate the mechanical behavior of saturated natural sand, thereby serving as a viable surrogate for visualization-based model tests of soil–structure interaction in geotechnical applications such as foundations and embankments.