Preliminary study on uniqueness of stress-strain envelope curves of sand
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摘要: 土体循环加卸载外包络线是否具有唯一性在认识土体固有属性上具有重要意义。基于土样全表面变形数字图像测量系统,选用硅微粉和福建标准砂为研究对象,开展了一系列三轴剪切试验和三轴循环加卸载试验,探索等应力幅值、阶梯应力幅值和随机应力幅值循环加卸载下应力-应变外包络线与相应的单调加载应力-应变曲线的一致性。试验结果表明土样在相同密度和围压条件下,单调加载的应力-应变曲线与经历不同循环应力历程的加卸载应力-应变外包络线近似一致,提出了砂土应力-应变外包络线的唯一性;讨论了循环应力历史和应力水平对曲线回归速度的影响以及应力-应变包络线唯一性在建立轴向应变累积模型中的应用。Abstract: The uniqueness of the stress-strain envelope curves of sand under cyclic unloading is of great importance in understanding the inherent properties of the sand. A series of monotonic triaxial compress tests and cyclic triaxial tests, considering constant amplitude, step stress amplitude as well as random stress amplitude, are conducted on the silica powder and Fujian standard sand to explore the consistency between the stress-strain envelope curves and monotonic curve by employing the full-surface digital image measurement system. The results show that the monotonic stress-strain curves of the soil samples with the same density and confining pressure are approximately consistent with the stress-strain envelope curves that undergo different cyclic stress processes, and the uniqueness of the stress-strain envelope curves of the sand is proposed. The influences of the cyclic stress history and stress level on the regression velocity of the curves and the application of the uniqueness of the stress-strain envelope curves in the establishment of the axial strain accumulation model are discussed.
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Keywords:
- stress-strain envelope curve /
- cyclic loading /
- sand /
- axial cumulative strain
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图 1 侧限加卸载和三轴加卸载下外包络线示意图
Figure 1. Sketch of envelope curves under oedometric compression and triaxial compression tests[25]
图 14 循环荷载下轴向应变累积投影方法示意[25]
Figure 14. Projection method for accumulation of axial strains during cyclic loading
表 1 试验材料的颗粒级配
Table 1 Particle gradations of test materials
试验材料 Gs 颗粒组成/% Cu 2~0.5
mm0.5~0.25
mm0.25~0.075
mm0.075~0.025
mm0.025~0.005
mm< 0.005 mm 硅微粉 2.68 0.00 0.90 15.34 43.38 31.45 8.93 2.62 福建标准砂 2.65 30.10 64.30 5.60 0.00 0.00 0.00 1.73 表 2 三轴单调剪切试验方案及强度
Table 2 Program and strengths of triaxial monotonic shear tests
试验编号 干密度/(g·cm-3) 围压/kPa 强度/kPa SP11 1.40 150 719 SP12 1.40 200 861 SP13 1.40 250 1068 SP14 1.40 300 1261 SP15 1.40 350 1470 SP16 1.40 400 1643 SP22 1.45 200 987 SP32 1.50 200 998 SP42 1.60 200 1112 FS42 1.60 200 502 表 3 三轴循环加卸载试验方案
Table 3 Programs of triaxial cyclic load tests
序号 试验编号 干密度/
(g·cm-3)围压/
kPa应力时间历程 循环次数/次 1 SP115 1.40 150 5 200 2 SP121 1.40 200 1 5 3 SP122 1.40 200 2 25 4 SP123 1.40 200 3 50 5 SP124 1.40 200 4 200 6 SP125 1.40 200 5 200 7 SP126 1.40 200 6 200 8 SP127 1.40 200 7 200 9 SP135 1.40 250 5 200 10 SP145 1.40 300 5 200 11 SP141 1.40 300 1 5 12 SP142 1.40 300 2 25 13 SP143 1.40 300 3 50 14 SP155 1.40 350 5 200 15 SP165 1.40 400 5 200 16 SP161 1.40 400 1 5 17 SP162 1.40 400 2 25 18 SP163 1.40 400 3 50 19 SP225 1.45 200 5 200 20 SP325 1.50 200 5 200 21 SP425 1.60 200 5 200 22 FS421 1.60 200 1 5 23 FS422 1.60 200 2 25 24 FS424 1.60 200 4 200 表 4 试验编号中数字含义
Table 4 Meanings of numbers in test number
数字位置 表示物理量 编号含义 1 2 3 4 5 6 7 第一位 干密度/(g·cm-3) 1.40 1.45 1.50 1.60 — — — 第二位 围压σ3/kPa 150 200 250 300 350 400 — 第三位 应力时间历程 1 2 3 4 5 6 7 -
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