The mechanical properties of soil-rock mixture (S-RM) can deform significantly under the influence of dry-wet cycles, affecting the safety of high-fill projects. A drying device was developed to perform direct shear tests on S-RM. Large-scale direct shear tests were carried out under the action of dry-wet cycling to study the effect of dry-wet cycling on the mechanical properties of S-RM. The open-source ImageJ software was used to identify the number and area of pores in the binary image, and the pore characteristics of S-RM under dry-wet cycles were analyzed. The results show that the section of post-peak in the shear stress-strain curve softens under the natural state (no dry-wet cycles), but it plasticizes under the application of the dry-wet cycles. The cohesion of S-RM particles is affected by the dry-wet cycling. It decreases significantly under the first dry-wet cycle and then decreases gradually for each successive cycle, after which it stabilizes during the fifth dry-wet cycle. The internal friction angle is not affected to a large degree. The effect of a dry-wet cycle on pores with different areas is significantly different. The pores with initial sizes of 0.5–10 mm2 decrease, while pores with other initial sizes are hardly affected by the dry-wet cycling. This paper quantitatively analyzed the relationship between the surface two-dimensional porosity and S-RM's cohesion and peak strain.

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