Shear characteristics and damage mechanism of carbonaceous mudstone soil-rock mixed fillers based on electrical resistivity

With carbonaceous mudstone increasingly employed as fill material for road embankments in areas of China such as Guangxi and Hunan, its long-term stability has become a significant engineering concern. This study adopted a test method combining direct shear and resistivity measurements. The dynamic coupling mechanism of the mechanical properties and resistivity response of carbonaceous mudstone soil-rock mixed fillers during the shear process was systematically investigated by controlling the influencing factors of rock content and normal stress. The study indicates that the filler's shear failure mode gradually shifts from strain softening to plastic flow as the rock content increases, with shear strength and strength parameters exhibiting an initial increase followed by a subsequent decrease. When the rock content exceeds 60%, particle breakage is markedly intensified, and an increase in normal stress further facilitates the breakdown of coarse particles. The resistivity of the specimen demonstrates a strong positive correlation with shear displacement. The initial resistivity exhibits a rising trend with increasing rock content, and variations in rock content notably impact the resistivity's extreme difference Δρ (Ω·m). 60% rock content is the key critical point of the shear strength, Br, and Δρ of the packing. At this point, the shear strength reaches the maximum value, the Br value undergoes a transition, and Δρ is the lowest. In this study, the variation of resistivity is utilized to characterize the evolution law of internal structural damage during the shear process, with the aim of providing a theoretical basis for the long-term stability analysis of carbonaceous mudstone soil-rock mixed fill embankments.