Research on the Crushing and Permeability Characteristics of Rockfill Materials Based on Fractal Matrix Model

Grading and permeability coefficient are key parameters that affect the engineering characteristics of rockfill materials(RFMs). During the process of dam filling, the particle breakage leads to the continuous evolution of the gradation of the RFMs, which causes the permeability coefficient to constantly change. Traditional pit testing and single ring water injection method were unable to conduct multiple tests on the same measuring point under different rolling variables, making it difficult to conduct in-depth research on the evolution of gradation and permeability characteristics of RFMs. This paper conducted a study on the gradation evolution and permeability characteristics of RFMs under different durations of vibration and rolling loading conditions based on a fractal matrix model. Firstly, a fractal matrix model was constructed to describe the evolution of experimental gradation. Then, single particle strength tests were carried out on the RFMs of Yulong Kashgar Hydropower Station. The modulus m was calculated based on the Wei bull distribution of single particle strength in the same particle group, and the size effect parameters were got by fitting the characteristic values of particle crushing energy consumption in different particle groups. Then, by screening each particle group and fitting it, the fractal dimension of its fractal fragmentation could be obtained. The effectiveness of the model and parameter calculation were verified by calculating the gradation of the RFMs under different vibration and rolling durations and comparing it with experimental values. By introducing the crushing parameter into the new Kim permeability coefficient calculation formula, an improved formula was proposed, which was suitable for calculating the permeability coefficient of RFMs. The permeability coefficient calculated by the new formula shows good consistency with the experimental values.