Granulometric fractal characteristics of argillaceous siltstone and their relationship with shear strength parameters

The correlation between the shear mechanical properties and fractal characteristics of argillaceous siltstone rockfill is critical for understanding dump slope stability.ObjectivesThis study aims to investigate the mechanical response characteristics of argillaceous siltstone rockfill under varying coarse grain contents and to analyze their correlation with fractal dimensions.MethodsLarge-scale direct shear tests were conducted on rockfill with different coarse grain contents. The relationship between shear strength parameters and fractal dimensions was examined， and the underlying mechanical response mechanisms were explored.ResultsThe results indicate that the shear strength of argillaceous siltstone rockfill is significantly influenced by coarse grain content. Under the same vertical pressure， shear strength increases with higher coarse grain content. For instance， at a vertical pressure of 2 000 kPa， increasing the coarse grain content from 20 % to 80 % led to a 19.66 % increase in shear strength. Shear strength parameters were closely related to coarse grain content： as coarse grain content increased， cohesion c decreased， whie the internal friction angle φ increased. The internal friction angle was more sensitive to changes in coarse grain content. The fractal dimension D decreased with increasing coarse grain content， reflecting particle gradation and heterogeneity. When D ranged from1.887 to 2.631， the rockfill exhibited well-graded characteristics. A co-rrelation was identified between fractal dimension D， coarse grain content， and shear strength parameters： D was positively correlated with cohesion c， but negatively correlated with coarse grain content P5 and internal friction angle φ.ConclusionsCoarse grain content significantly affects the mechanical properties of argillaceous siltstone rockfill. Additionally， the fractal dimension serves as a critical parameter for evaluating gradation and heterogeneity in rockfill materials.