SIMULATION MODELING AND SAMPLE SIZE EFFECT ANALYSIS FOR GRAVEL SOIL TRIAXIAL TEST
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摘要: 借助离散单元理论与室内三轴试验, 分析碎石土物理实验中试样尺寸(直径和高度)变化对应力应变、体应变、粘聚力和内摩擦角等力学性能的尺寸效应影响。研究结果表明, 所提出的块体随机生成法则能较好地实现试样中不同形状碎石块的模拟。不同直径和高度的碎石土试样, 初始2%应变范围内的应力-应变曲线变化规律基本一致, 后部曲线变化较大。直径和高度越小, 围压越低, 应力软化现象越明显; 直径大于250 mm、高度大于350 mm后无应变软化, 残余应力恒定。峰值应力随试样直径增大以25%的增长率呈线性增长, 随高度的增大呈非线性增长, 高度小于200 mm时增长率为11.9%, 大于200 mm后为28.9%。体应变破坏峰值则表现为先增大后减小的趋势。同时粘聚力随直径的增大线性增长, 内摩擦角则减小, 而试件高度的变化对其影响规律则相反。Abstract: Based on the size effect in the gravel soil physics experiment, mechanical properties of the stress-strain, the strain, the cohesive force and inner friction angle of gravel soil was analyzed using discrete element theory and indoor triaxial test. The results showed that the proposed block generated law could realize the simulation of the crushed stone much more. The stress strain curves were almost unanimous (2% strain) at different diameter and height, but the rear part of the curve changes greatly, the smaller the diameter and height, the lower confining pressure stress, the more obvious softening phenomenon. The residual stress was constant after diameter 250 mm, height 350 mm. The peak stress increased with a linear growth rate of 25% with the sample diameter, but nonlinear growth along with the increase of height, when less than 200 mm, the high growth rate was 11.9%, and 28.9% after 200 mm. Damage body strain values were first increasing then decreasing, at the same time cohesive force increases of the linear growth with the diameter and in friction angle was reduced, but rule was just the opposite at different height.
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Key words:
- gravel soil /
- triaxial simulation /
- size effect
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表 1 模拟级配与试样级配对比
Table 1. Comparison of simulated grading and sample grading
三轴试验试样尺寸和级配 数值模拟模型尺寸和级配 试样尺寸/mm 粒径/mm 含量/% 模型尺寸/mm 粒径/mm 含量/% 101×200 20~10 21.72 101×200 20~10 21.72 10~5 20.19 10~5 20.19 5~2 18.09 5.0~2.5 18.09 ＜2 40 2.5 40 
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表 2 参数标定值
Table 2. The calibration parameters
参数含义 程序代码 参数取值 杨氏模量 md_Ec 4.5e6 平行粘结模量 pb_Ec 1e7 密度 md_dens 2600 土颗粒法向刚度 kn 7.2e4. 块体法向刚度 kn 4e5 法向刚度与切向刚度比 kn/ks 0.8 接触粘结法向力平均值 cb_sn_mean 1.35e5 接触粘结切向力平均值 cb_ss_mean 1.35e5 平行粘结法向力平均值 pb_sn_mean 7e4 平行粘结切向力平均值 pb_ss_mean 7e4
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表 3 模拟实验与三轴试验误差分析
Table 3. Error analysis in simulation experiment and triaxial test
实验类型 峰值偏应力/kPa 粘聚力c/kPa 内摩擦角φ/(°) 围压100 kPa 围压200 kPa 围压400 kPa 三轴试验 501.80 677.90 1119.20 79.89 30.67 模拟实验 466.91 708.41 1016.43 91.33 28.38 误差/% 6.95 4.50 9.18 14.30 7.45
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表 4 数值模拟工况组合
Table 4. Numerical simulation case combinations
编号 试样尺寸/mm 直径 高度 试样1 50 200 试样2 70 200 试样3 101 200 试样4 150 200 试样5 200 200 试样6 250 200 试样7 101 100 试样8 101 150 试样9 101 200 试样10 101 250 试样11 101 300 试样12 101 350
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表 5 不同试样直径下峰值体应变
Table 5. Peak body strain under different diameter
试样直径/
mm峰值体应变 100 kPa 200 kPa 400 kPa 50 0.0264 0.0481 0.0174 70 0.0326 0.0477 0.0452 101 0.0568 0.0587 0.0372 150 0.0286 0.02840 0.03640 200 0.0113 0.00983 0.00282 250 -0.0021 -0.01360 -0.03350
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表 6 不同试样高度下峰值体应变
Table 6. Peak body strain under different height
试样高度/
mm峰值体应变 100 kPa 200 kPa 400 kPa 100 0.0279 0.0121 0.0074 150 0.0379 0.0309 0.0151 200 0.0568 0.0587 0.0372 250 0.0557 0.0448 0.0912 300 0.0563 0.0462 0.0396 350 0.0133 0.0137 0.0888
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