Influences of soluble salt content on mechanical properties of Ili undisturbed loess
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摘要: 为揭示非饱和伊犁原状黄土的湿、载屈服特性及水量变化特性,采用非饱和土三轴仪,开展不同易溶盐含量下的控制吸力的净平均应力增减试验、控制净平均应力的吸力增减试验和控制净围压和吸力的固结剪切试验,探究易溶盐含量对非饱和伊犁黄土变形、屈服和水量变化特性的影响规律。研究结果表明：含盐量对提高颗粒间的胶结作用存在临界值,在14～20 g/kg含盐量区间存在峰值屈服净平均应力、峰值屈服剪应力,且加载增湿屈服线和剪切屈服线最大；随含盐量增加,压缩性指标降低、固结排水量减小；含盐量对水量的影响主要在土水特征干燥曲线的过渡区,但对吸力增加屈服线影响不大；盐分过量和吸力降低均可使非饱和伊犁黄土产生屈服。Abstract: In order to reveal the loading collapse yield and moisture characteristics of the unsaturated Ili undisturbed loess, a series of net mean stress increase-decrease tests on control suction, suction increase-decrease tests on control net mean stress, consolidation shear tests on control net confining pressure and suction under different soluble salt contents are carried out by using the unsaturated soil triaxial apparatus. The effects of soluble salt content on the deformation, yield and moisture of the unsaturated Ili loess are studied. The results show that there is a critical value for salt content to improve the cementation between particles. There are the peak yield net mean stress and the peak yield shear stress between 14 and 20 g/kg of salt content, and the loading collapse yield curve and the shear yield curve are the maximum. The compressibility index and moisture change at the consolidation stage decrease with the increase of salt content. The influences of salt content on moisture are mainly in the transition region of soil water characteristic drying curve, but there are few effects on the suction increase yield curve. The unsaturated Ili loess can be yielded by being excessively salting and reducing suction.
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Keywords:
- unsaturated soil /
- Ili loess /
- soluble salt /
- yield characteristic /
- moisture characteristic
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图 2 净平均应力循环试验的压缩–回弹曲线
Figure 2. Compression-rebound curves of net mean stress cycle tests
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图 7 净平均应力循环试验的水量变化关系（θ=5 g/kg）
Figure 7. Moisture change under net mean stress cycle tests (θ=5 g/kg)
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图 8 水相体变指标
λw(s) 与含盐量θ的关系Figure 8. Curves of index of moisture volume change and salt content
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图 11 吸力循环试验中饱和度Sr与吸力s的曲线
Figure 11. Curves of degree of saturation and suction in suction cycle tests
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图 12 吸力循环试验的体应变、水相体变和归一化吸力的关系
Figure 12. Relationship among volume strain, moisture volume change and normalized suction in suction cycle tests
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图 13 不同净围压下剪切体应变与应力比的关系
Figure 13. Relationship between shear strain and stress ratio under different mean confining pressures
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图 15 剪切过程中试样的含水率和净平均应力的关系
Figure 15. Relationship between water content of specimens and net mean stress during shearing
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图 16 剪切完成后试样的含水率和θs/(σ3-ua)的关系
Figure 16. Relationship between water content of specimens and θs/(σ3-ua) after shearing
表 1 试验方案及加荷顺序（以一个含盐量为例）
Table 1 Test schemes and loading sequence (taking a salt content as an example)
试验类型 应力状态 加荷过程/kPa 净平均应力循环 初始吸力 5/ 50/ 100/ 150 净平均应力 5→100→20→300→100→400 吸力循环 初始吸力 5 净平均应力 100 吸力 5→100→25→150 固结剪切 吸力 5/ 50/ 100/ 150 净围压 100/ 200/ 300 注： 净平均应力循环试验中净平均应力小于100 kPa时,荷载变化20 kPa/级；净平均应力大于100 kPa时,荷载变化50 kPa/级；吸力循环试验中荷载变化25 kPa/级。
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表 2 试样排水量的量测值与校正值比较
Table 2 Comparison between measured and corrected values of amount of water discharge from specimens
试验类型 含盐量θ/(g·kg-1) 量测值/cm3 校正值/cm3 差值/cm3 相对误差/% 吸力循环试验(p=100 kPa) 5 33.53 32.5 1.03 3.18 14 36.57 35.64 0.93 2.61 26 33.79 32.17 1.62 5.04
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表 3 不同含盐量下的系数值
Table 3 Coefficients under different salt contents
系数 5 g/kg 8 g/kg 14 g/kg 20 g/kg 26 g/kg κ100均值 0.008 0.009 0.009 0.009 0.009 κ300均值 0.016 0.018 0.019 0.019 0.016 λs/(10-3) 1.3 0.8 0.4 0.7 0.8
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表 4 应力交点处的
εv 和εw Table 4 Values of
εv andεw at intersection of stress类别 εv /%εw /%s/kPa 0 50 100 150 0 50 100 150 p/kPa 100 100 100 100 100 100 100 100 ① 9.7 3.5 2.5 2.4 7.8 1.6 3.0 0.4 ② 12.0 17.1 23.5 26.4 0.2 9.4 28.4 34.9 ③ 13.9 6.0 4.4 5 10.9 0.6 0.2 0.1 注： ①、②、③分别表示净平均应力循环、吸力循环和固结剪切试验。
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