The Scale Effect of Sand and Gravel Materials in Riverbed Cover Layers Based on Large-Scale Triaxial Tests

Abstract In response to the difficulty of conducting in-situ tests on the gravel materials of riverbed cover layers, this study investigates their mechanical properties using a scaled-down grading method. Three methods, namely the equivalent substitution method, the similar grading method, and the hybrid method, are employed based on the original grading of the gravel materials from riverbed cover layers. Through large-scale triaxial consolidation drainage shear tests, the study investigates the effects of the reduction factor 𝑀 of the maximum particle size and confining pressure on the stress-strain relationship, fractal dimension, particle breakage, and parameters of the Duncan-Chang E-B model. It reveals the influence pattern of scaling based on fractal dimension and particle breakage rate on the strength and deformation of gravel materials. The results indicate significant differences in the scaling effects among the three scaling methods. Among them, under the same confining pressure, the gravel material strength obtained by the similar grading method is the highest, with the smallest difference in fractal dimension before and after the test and the lowest particle breakage rate, followed by the hybrid method. Moreover, with the increase in 𝑀 value, the peak stress gradually increases, manifested by the increase in the parameters k and Kb of the E-B model, with the values increasing by 4.5 times and 3.3 times, respectively, when M = 15 compared to 𝑀 =0. The research findings can provide important experimental basis for the stability analysis and deformation analysis of dam bodies.