Experimental Study on Permeability of Soil–Phyllite Mixture in Northwest Sichuan

The soil–phyllite mixtures are widely distributed in the northwest of Sichuan, and excavation of slopes in these areas under rainfall conditions can cause large-scale instability, posing threats to the safety of transportation engineering construction and operation. The permeability characteristics of soil–rock mixtures significantly affect the stability of excavated slopes, and the spatial orientation of flat phyllite is the key factor affecting the permeability of soil–phyllite mixtures. Based on the spatial orientation characteristics of phyllite, a self-developed large-scale permeameter was used to examine permeability characteristics of soil–phyllite mixtures under different conditions, including various rock content and particle sizes, and the influence of these factors on the permeability of such mixtures was studied. The results show that when the rock content increases from 0% to 35%, the permeability coefficient of the mixture decreases by 49.28%, while the critical and failure hydraulic gradients increase by 159.38% and 54.17%, respectively, making piping failure less likely to occur. When the rock size increases from 20–40 mm to 60–80 mm, the permeability coefficient increases by 34.62%, and the critical and failure hydraulic gradients decrease by 23.15% and 10.3%, respectively, making piping failure more likely to occur. These findings provide references for evaluating the hydraulic characteristics of soil–phyllite mixtures and assessing the excavated slope stability in northwest Sichuan.