This study investigates the behaviour of dense clayey and silty sands with kaolinite clay under static drained/undrained conditions at low confining stress. Conventional laboratory tests assessed the mixtures’ physical properties, but standard void ratio methods proved inadequate for silty sands with clay. Despite targeting 80% relative density, specimens exhibited loose sand behaviour in both drained and undrained tests. Analytical redefinition of minimum/maximum void ratios (based on sand-clay volumetric fractions) improved specimen reconstitution, yielding dense behaviour matching host sand performance. However, these methods are limited to non-expansive, low-plasticity clays. Void ratios in clayey silty sands depend on confining stress, drainage, saturation, clay content, and sand skeleton structure. Unlike pure sands, these mixtures experience variable void ratios due to clay phase changes under different saturation levels. A new evaluation method is needed, accounting for clay composition, saturation-dependent consistency, and initial sand skeleton configuration to accurately characterise these soils. The findings highlight the limitations of conventional approaches and stress the need for advanced frameworks to model complex soil behaviour in geotechnical applications.