## 6 Conclusions  
(1) The shear strength of argillaceous siltone rockfill materials is closely related to and significantly affected by the coarse grain content and the number of reciprocating shears. The shear strength increases with the coarse grain content and decreases with the number of reciprocating shears. In addition, the forward shear strength is greater than the reverse shear strength, and the two are approximately symmetrically distributed about the x-axis.  
(2) The hysteresis loop area and damping ratio of soil samples with the same coarse grain content tend to decrease with the number of reciprocating shears. With the same number of reciprocating shears, the hysteresis loop area of the soil samples increasesgradually with the coarse grain content, while the damping ratio is not correlated with the coarse grain content.  
(3) The shear strength parameter of argillaceous siltstone rockfill materials is significantly affected by the coarse grain content and the number of reciprocating shears. The internal friction angle and cohesion increase with the coarse grain content and gradually decrease with the number of reciprocating shears.  
(4) When the coarse grain content is \(P_{5}=27.56\%\), \(P_{5}=38.02\%\), \(P_{5}=61.34\%\), and \(P_{5}=75.43\%\), respectively, the shear stiffness of argillaceous siltstone rockfill increases linearly with the increase of the coarse grain content. The shear stiffness ratio has a logarithmic function relationship with the number of reciprocating shears. The shear stiffness of argillaceous siltstone rockfill is related to the coarse grain content and the number of reciprocating shears.  
(5) The variability of the mineral composition and fabric characteristics of rockfill materials is the principal cause of their strength deterioration, and reciprocating shear serves as the trigger and changes the original spatial soil grain distribution and contact pattern. As the grain fragmentation intensifies, the interlocking among the block grains weakens, and the soil shear strength shows a trend of gradual deterioration.  
Conceptualization, J.D. and Z.X.; methodology, D.L., X.S. and W.Z.; validation, D.L., C.L. and W.Z.; resources, J.D.; data curation, Z.X.; writing--original draft preparation, J.D., Z.X. and D.L.; writing--review and editing, X.S., C.L. and W.Z.; supervision, J.D.; project administration, J.D.; funding acquisition, J.D. All authors have read and agreed to the published version of the manuscript.  
This work is supported by the Special Basic Cooperative Research Programs of the Yunnan Provincial Undergraduate University's Association (202101 BA070001-137), the Basic Research Project of the Yunnan Province of China (202101 AT070144), and the Talent Introduction Program of Kunming University (XJ20220015).  
The original contributions presented in the study are included in the article, and further inquiries can be directed to the corresponding author.  
The authors particularly appreciate the valuable comments made by the editors and reviewers to make a substantial improvement to this manuscript.  
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflicts of interest.