Study on the permeability coefficient of weathered red sandstone soil based on laboratory constant-head permeability tests

Weathered red sandstone soil is widely distributed across Southwest China, and its permeability is significant to the stability of slope and subgrade engineering. This study conducts a series of constant-head permeability tests on weathered red sandstone soil to examine how the permeability coefficient ( k 20 ) is affected by void ratio ( e ), curvature coefficient ( C c ), uniformity coefficient ( C u ), and particle size. The experimental results indicate that the k 20 of the tested soil ranges from 1.03 × 10 −4 to 1.68 × 10 −2 cm/s and exhibits a strong linear positive correlation with ten to the power of the void ratio. Under conditions of consistent e and effective particle size ( d 10 ), k 20 increases linearly with increasing C c and C u . Among the influencing factors, particle size is identified as a key factor affecting k 20 , with a strong linear relationship between k 20 and \({d}_{10}^{2}\) . Based on the experimental data, a multifactor predictive model integrating e , C c , C u , and d 10 is developed. The results demonstrate that the ratio between the calculated values and the measured values generally falls within the range of 0.64 to 3.87, indicating a substantial improvement in predictive accuracy compared to traditional empirical formulas. These findings provide a theoretical basis for seepage stability analysis, drainage design, and geological disaster prevention of slopes in regions where weathered red sandstone soil is distributed.