Experimental Study on the Influence Characteristics of Gravel Particle Size Variation on the Shear Strength Parameters of Rock Soil Mixture Based on PFC Numerical Simulation
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摘要: 为了探究碎石粒径变化和大碎石含量对土石混合体抗剪强度参数内摩擦角的影响特征，本文采用离散元PFC 3D，并基于西南某泥石流堆积体级配特征，对其粒径大小从10～60 mm和大粒径碎石含量从10%～90%等试样构建岩土体柔性三轴数值模型共计44个，开展数值试验分析。模拟结果表明：对比相同粒径的均匀圆形颗粒模型与不规则碎石模型，其内摩擦角随着粒径的增大呈现出增大趋势，且后者内摩擦角大于前者，最大内摩擦角分别达到39.05°和43.27°；当碎石粒径<30 mm时内摩擦角的增幅不明显；相同粒径条件下，碎石模型的内摩擦角大于均匀圆形颗粒模型，揭示了内摩擦角会受到碎石颗粒形状的影响；大碎石含量对岩土体内摩擦角起着一定的控制作用，对比混合粒径碎石模型和土石混合模型，其内摩擦角随大碎石含量的增大而增大，前者内摩擦角的增幅小于后者，当大碎石含量>50%时内摩擦角的增幅较为明显，两者内摩擦角的增幅分别为8.34°和14.08°；当粒径分布特征指标中的限制粒径d60在10～30 mm，其内摩擦角随d60的增大而增大，当d60>30 mm后，其内摩擦角随d60的增大而减小。Abstract: To investigate the impact of gravel size variations and the influence of large gravel content on the internal friction angle of shear strength parameters in soil-rock mixtures, this study constructed a total of 44 flexible boundary triaxial numerical models of geotechnical bodies using the discrete element method (PFC 3D) and referencing the grading characteristics of a debris flow accumulation body in the southwest. The simulation results indicate that, compared to uniform circular particle models of the same size, the internal friction angle of irregular gravel models exhibits an increasing trend with the increase in particle size, and the internal friction angle of the latter is larger than that of the former, reaching maximum values of 39.05° and 43.27°, respectively. When the gravel size is less than 30 mm, the increase in internal friction angle is not significant. Under the same particle size conditions, the internal friction angle of the gravel model is greater than that of the uniform circular particle model, revealing that the internal friction angle is influenced by the shape of the gravel particles. The content of large gravel plays a certain controlling role in the internal friction angle of the geotechnical body. When comparing mixed-size gravel models to soil-rock mixture specimens, the internal friction angle increases with the increase in large gravel content, with the increase amplitude of the former is less significant than that of the latter. When the large gravel content exceeds 50%, the increase in internal friction angle becomes more significant, with the increases of 8.34° and 14.08°, respectively. When the characteristic particle size d60 in the characteristic index of particle size distribution is 10 mm～30 mm, the internal friction angle increases with the increase of d60. When d60>30 mm, the internal friction angle decreases with the increase of d60.
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图 2 土石混合试样抗剪强度参数与含石量关系
Figure 2. The relationship between shear strength parameters and stone content of soil rock mixed samples
图 3 细观参数标定结果与室内三轴试验结果对比图
Figure 3. Comparison of micro-scale parameter calibration results with indoor triaxial test results
图 5 均匀颗粒模型和其对应碎石三轴模型
Figure 5. Uniform particle model and its corresponding crushed stone triaxial model
图 6 混合粒径碎石模型和土石混合级配模型
Figure 6. Model of mixed-size crushed stone and gradation model of soil-rock mixtures
图 8 30 mm粒径的均匀颗粒模型和碎石模型的偏应力-应变结果
Figure 8. Stress-strain results for uniform particle and crushed stone models with a 30 mm particle size
图 9 均匀模型和碎石模型内摩擦角随粒径变化的对比图
Figure 9. Comparison of internal friction angle varying with particle size between the uniform and gravel models
图 11 大粒径含量70 %的碎石模型和土石混合级配模型的偏应力-应变结果
Figure 11. Deviatoric stress-strain results for the crushed stone model with 70% large particle size and the soil-rock mixed gradation model
图 12 混合粒径碎石模型内摩擦角随60 mm大碎石含量的变化
Figure 12. The variation of internal friction angle of mixed particle size crushed stone model with 60 mm large crushed stone content
图 13 土石混合模型内摩擦角随60 mm大碎石含量的变化
Figure 13. The variation of internal friction angle of soil-rock mixed model with 60 mm large gravel content
图 14 土石混合模型内摩擦角随d60的变化规律
Figure 14. The variation law of internal friction angle with d60 in soil-rock mixed model
表 1 试样细观参数取值
Table 1. Meso-parameters values of the specimen
接触类型 密度/(kg·m−3) 有效模量/(N·m−2) 刚度比 摩擦系数 ball-facet — 2×108 1.5 0.5 pebble-facet — 2×108 1.5 0.5 pebble- pebble 2.5×103 1×108 1.5 0.5 ball-pebble — 1×108 1.5 0.5 ball-ball 2.0×103 1×108 1.5 0.5 
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