Mechanical properties of salinized aeolian sand under freeze-thaw cycles
Article Text (Baidu Translation)
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摘要: 为研究季冻区沙漠边缘盐渍化风积沙力学特性，在冻融循环条件下对不同含盐量风积沙开展了三轴不固结不排水剪切试验，为研究冻融循环后不同含盐量风积沙应力-应变关系曲线与抗剪强度的劣化规律，提出了一种考虑围压与冻融循环次数条件下修正的邓肯-张模型，并引入抗剪强度劣化度描述风积沙强度衰减速度，提出了冻融循环次数与含盐量对风积沙抗剪强度的耦合作用计算公式。研究结果表明：不同冻融循环次数、含盐量与围压下风积沙应力-应变曲线均表现为应变软化型，冻融循环状态下的盐渍化风积沙受到温度与盐分的耦合作用，随着冻融循环次数与含盐量的增加，风积沙应变软化速率显著降低；修正的邓肯-张模型可以较好地描述风积沙应变软化特征，不同冻融循环次数下风积沙初始回弹模量随围压增大而增大，随冻融循环次数增加先减小后缓慢增加；在冻融条件下，无盐风积沙抗剪强度劣化速率较慢，而对于含盐风积沙，土中的盐分与水分相变加快了风积沙抗剪强度的劣化速率，使得风积沙抗剪强度迅速降低；对于不同围压下的风积沙，其强度变化规律相似，即在经历初次冻融循环后抗剪强度显著下降，并随着冻融循环次数的增加，强度劣化速率逐渐趋于稳定，风积沙抗剪强度劣化度随冻融循环次数增加呈双曲线递增，随含盐量的增大呈线性递增趋势。Abstract: In order to study the mechanical properties of salinized aeolian sand at the edge of the desert in the monsoon freezing zone, triaxial unconsolidated and undrained shear tests were carried out on the aeolian sands with different salt contents under freeze-thaw cycle conditions. To study the stress-strain relationship curves and deterioration laws of shear strengths of aeolian sands with different salt contents after freeze-thaw cycles, a modified Duncan-Zhang model considering the conditions of perimeter pressure and the number of freeze-thaw cycles was proposed. The shear strength deterioration degree was introduced to describe the rate of strength decay of aeolian sand, and the formula for calculating the coupling effect of the number of freeze-thaw cycles and salt content on the shear strength of aeolian sand was proposed. Research results show that the stress-strain curves of aeolian sands with different numbers of freeze-thaw cycles, salt contents, and perimeter pressures are all the strain-softening type. The salinized aeolian sand under freeze-thaw cycles is subjected to the coupling of temperature and salinity, and the strain softening rate of aeolian sand decreases significantly with the increases in the number of freeze-thaw cycles and salt content. The modified Duncan-Zhang model can better characterize the strain softening of aeolian sand. The initial resilience moduli of aeolian sand under different numbers of freeze-thaw cycles increase with the increase in the perimeter pressure, and decrease first and then increase slowly with the number of freeze-thaw cycles. Under the freeze-thaw conditions, the deterioration rate of shear strength of unsalted aeolian sand is slow. In the case of the salinized aeolian sand, the phase changes in the salt and moisture in the soil accelerate the deterioration rate of aeolian sand shear strength, leading to a rapid decrease in the shear strength of aeolian sand. For the aeolian sand under different perimeter pressures, the patterns of strength change are similar, and the shear strengths decrease significantly after the initial freeze-thaw cycle. As the number of freeze-thaw cycles increases, the deterioration rates of strength are gradually stable. The shear strength deterioration degree of aeolian sand increases hyperbolically with the number of freeze-thaw cycles and linearly with salt content.
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Key words:
- subgrade engineering /
- aeolian sand /
- triaxial test /
- freeze-thaw cycle /
- salt content /
- stress-strain /
- deterioration model
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图 1 颗粒粒径级配曲线与扫描电镜
Figure 1. Particle size grading curve and scanning electron microscopy
图 2 不同冻融循环次数风积沙应力-应变曲线
Figure 2. Stress-strain curves of aeolian sand with different numbers of freeze-thaw cycles
图 4 不同冻融循环次数下风积沙SEM
Figure 4. SEMs of aeolian sand under different numbers of freeze-thaw cycles
图 5 3%含盐风积沙应力-应变转换曲线
Figure 5. Stress-strain transition curves for 3% salinized aeolian sand
图 6 风积沙抗剪强度与冻融循环次数的关系
Figure 6. Relationship between shear strength and number of freeze-thaw cycles for aeolian sand
图 8 冻融循环次数与劣化度的关系
Figure 8. Relationship between number of freeze-thaw cycles and deterioration degree
表 1 风积沙基本物理性质
Table 1. Basic physical properties of aeolian sand
不均匀系数 曲率系数 最大干密度/ (g·cm-3) 最优含水率/ % 土粒比重 2.50 0.90 1.72 11.80 2.60 
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表 2 三轴剪切试验方案
Table 2. Program of triaxial shear test
冻结温度/℃ 围压/kPa 含盐量/% 冻融循环次数 -20 50、100、150 0 0、1、3、6、9 -20 50、100、150 3 0、1、3、6、9 -20 50、100、150 5 0、1、3、6、9
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表 3 3%含盐风积沙应力-应变拟合参数
Table 3. Stress-strain fitting parameters for 3% salinized aeolian sand
冻融循环次数 围压/kPa a/10-2 b c/10-2 E0/kPa R2 0 50 6.27 -19.35 -6.03 417.04 0.995 0 100 3.17 -24.58 -2.98 520.00 0.999 0 150 3.55 -20.17 -3.41 729.44 0.953 1 50 4.60 -23.80 -4.30 340.17 0.999 1 100 9.16 -25.08 -8.95 471.89 0.997 1 150 2.47 -19.38 -2.26 476.56 0.999 3 50 7.99 -24.91 -7.59 249.54 0.999 3 100 8.56 -40.83 -8.36 507.18 0.999 3 150 2.46 -19.91 -2.27 509.65 0.998 6 50 9.93 -28.88 -9.57 279.50 0.999 6 100 4.66 -24.30 -4.49 575.97 0.999 6 150 2.46 -18.14 -2.28 576.32 0.997 9 50 1.43 -33.22 -1.40 337.09 0.999 9 100 7.02 -31.01 -6.85 574.77 0.999 9 150 2.33 -17.77 -2.16 575.33 0.997
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