Experimental study on seepage characteristics of soil–rock mixtures with different fractal dimensions of particle size in fault zone

This paper takes the Sanshan Island fault zone as the engineering background, conducts permeability tests, and combines fractal theory to study the permeability characteristics of soil–rock mixtures (S-RMs) with different rock-block proportions (20%, 30%, 40%, 50%, 60%, and 70%) in the fault zone and their corresponding relationship with fractal dimensions of particle size (FDPS). The main conclusions drawn are as follows: (1) The S-RM within the Sanshan Island fault zone exhibits fractal characteristics, with FDPS ranging from 2.05 to 2.59 for both soil and rock-block particles. (2) The linear fitting degree between the rock-block proportion of the S-RM and the fractal dimensions of particle size of the rock-block particles reaches 0.92, which can be used as a bridge to study the permeability characteristics of S-RM with different fractal dimensions of particle size. (3) As the seepage pressure increases, the permeability coefficient of the S-RM gradually increases, and the relationship between seepage pressure and permeability coefficient can be described by a power function. (4) As the FDPS increases, the permeability coefficient of S-RM shows a trend of first decreasing and then increasing. When the seepage pressure is 0.03 MPa, the FDPS increases from 2.227 to 2.647, and the permeability coefficient decreases from 5.47 × 10−6 to 3.14 × 10−6 cm/s. During the process of increasing the FDPS from 2.647 to 2.899, the permeability coefficient increased from 3.14 × 10−6 to 4.97 × 10−6 cm/s. (5) For S-RM with the same rock-block proportion, as the particle size and distribution range of the rock blocks increase, the fractal dimension of the particle size of the S-RM gradually increases, and the permeability coefficient gradually decreases.