Gradation of Subgrade Soil and Its Salt-Resistance Effect in Salt Lake Area in Qinghai
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摘要: 青海盐湖地区的路基工程处于隐蔽性盐风化作用强烈的寒旱岩土环境. 分别采取青海茶卡盐湖地区工程建设层天然盐渍土土样和已建路基结构土层土样，研究青海盐渍土地区路基结构防护盐风化作用的效果. 通过易溶盐含量测定、颗粒分析实验和毛细管水上升实验，对青海茶卡盐渍土区路基结构土层中的毛细管水上升最大高度开展理论计算. 研究表明：青海茶卡地区盐渍土中毛细水上升高度大于一般土中毛细水上升高度，细粒组（0.250～0.075 mm）含量有利于水盐运移上升，粗粒组（> 0.250 mm）含量不利于水盐运移上升；在水盐运移和汽盐运移双重作用下，茶卡盐渍土地区路基结构土层均出现次生盐渍化现象，建议在茶卡盐渍土地区的路基工程中，设置卵砾石阻盐隔断层的粒组级配范围控制在2.0～5.0 mm之间，该粒组含量大于75%，厚度在300.0～1000.0 mm为宜；阻盐隔断层的设置位于路堤上部，高于一般路基规范中规定的高度，可以提高阻止水盐运移上升、增强汽盐淋滤作用的效果.Abstract: A subgrade project in Qinghai salt lake area, China was in a cold and dry geotechnical environment with strong concealed salt weathering. Taking the natural saline soil samples of the above subgrade construction project and soil samples of the built subgrade structure in Chaka Salt Lake area of Qinghai, comparative tests were conducted to study the effect of the subgrade structure protection against salt weathering in the saline soil area of Qinghai province. On the basis of soluble salt content measurements, particle analysis and capillary water rising experiment, the maximum height of capillary water rising in subgrade soil layer in Chaka saline soil area was calculated theoretically. The results indicate that the rising height of capillary water in the saline soil was higher than that in the general soil; the content of fine grains (0.250–0.075 mm) was conducive to the increase of water and salt migration, while the content of coarse grains (> 0.250 mm) would inhibit water and salt migration. Under the dual action of water and salt migration and vapor salt migration, secondary salinization occurred in the subgrade soil layer of Chaka saline soil area. It was suggested to set up the gravel salt-blocking layer in the subgrade project of the Chaka saline land area; the grading range of particles should be controlled between 2.0 and 5.0 mm, and the fraction of grains in this size range should be greater than 75%, while the thickness of the gravel salt-blocking layer should be between 300.0 and 1000.0 mm. Besides, the location of the blocking layer should be on the upper part of the embankment, higher than the height specified in the general subgrade code, which can improve the effect of preventing the movement of water-salt and enhancing the effect of vapor-salt leaching.
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图 4 茶卡盐湖盐区渍土水盐运移上升h-t关系
Figure 4. h-t curve for water and salt migration in saline soil of Chaqia Salt Lake
图 5 研究路基结构土层开挖及设计截面
Figure 5. Excavation and design sections of the subgrade structure soil layer (unit： m)
图 7 路基土层结构及颗粒特征分组
Figure 7. Structure of subgrade soil layers grouped by particle characteristics
图 8 路基粗粒土颗粒级配曲线
Figure 8. Particle gradation curves of coarse-grained subgrade soil at different depths
图 9 路基土层级配与毛细水上升高度相关性
Figure 9. Correlation between subgrade soil gradation and rise height of capillary water
表 1 研究区盐渍土易溶盐含量
Table 1. Soluble salt content in saline soil of chaqia lake
取样深
度/mCl−/
(mol•kg−1)SO42−/
(mol•kg−1)离子比 含盐
量/%盐渍
土类0 24 12.0 1.000 0.42 A 0.2 24 25.2 0.476 0.55 B 0.4 16 25.6 0.313 0.52 B 0.6 28 34.8 0.402 0.70 B 0.8 16 45.0 0.178 0.78 C 1.0 28 18.0 0.778 0.51 B 1.2 16 12.8 0.625 0.36 B 1.4 20 12.4 0.806 0.32 B 1.7 12 18.4 0.326 0.42 B 2.0 16 12.4 0.645 0.34 B 2.3 12 86.8 0.069 1.33 C 2.6 16 36.0 0.222 0.64 C 3.0 20 70.4 0.142 1.18 C 注：A为亚氯盐渍土；B为亚硫酸盐渍土；C为硫酸盐
渍土.
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表 2 研究区盐渍土的毛细管实验土样粒级配情况
Table 2. Grading of soil samples in capillary experiment of saline soil in the study area
试验编号 粒组的含量/% 装土质量/g 含水
率/%（2.000～
0.250] mm
（粗粒组）（0.250～
0.100] mm
（中粒组）（0.100～
0.075] mm
（细粒组）1# 75 25 1783 0.2 2# 75 25 1812 0.2 3# 25 75 1833 0.2 4# 75 25 1866 0.2 5# 50 25 25 1877 0.2 6# 25 50 25 1880 0.2
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表 3 路基结构层级配粒径及参数
Table 3. Characteristic particle sizesand parameters of subgrade soil layer at different depths
取样深
度/md60/mm d30/mm d10/mm Cu Cc 0.2 0.360 0.150 0.066 5.455 0.947 0.4 0.850 0.210 0.120 7.083 0.432 0.6 0.480 0.164 0.086 5.581 0.652 0.8 0.460 0.160 0.087 5.287 0.640 1.0 0.260 0.140 0.084 3.095 0.897 1.2 0.260 0.140 0.080 3.250 0.942 1.4 0.280 0.140 0.080 3.500 0.875 1.6 0.600 0.160 0.082 7.317 0.520 1.8 0.460 0.138 0.080 5.750 0.518 2.0 0.470 0.165 0.086 5.465 0.674 2.2 0.480 0.165 0.087 5.517 0.652 2.4 0.620 0.148 0.086 7.209 0.411 2.6 0.270 0.126 0.075 3.600 0.784
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表 4 路基结构土层级配及水盐运移上升高度计算结果
Table 4. Calculation results of soil gradation and rise height of water and salt migration in subgrade soil layers
路基结构层 取样深度/m d60/mm d30/mm d10/mm Cu h/mm ① 0.2 0.360 0.150 0.066 5.455 989.3 ② 0.4 0.850 0.210 0.120 7.083 1521.7 ③ 0.6 0.480 0.164 0.086 5.581 1047.3 0.8 0.460 0.160 0.087 5.287 957.1 ④ 1.0 0.260 0.140 0.084 3.095 92.2 ⑤ 1.2 0.260 0.140 0.080 3.250 136.7 1.4 0.280 0.140 0.080 3.500 258.5 1.6 0.600 0.160 0.082 7.317 1907.7 1.8 0.460 0.138 0.080 5.750 1377.8 ⑥ 2.0 0.470 0.165 0.086 5.465 979.4 2.2 0.480 0.165 0.087 5.517 1012.5 2.4 0.620 0.148 0.086 7.209 2022.1 2.6 0.270 0.126 0.075 3.600 427.2
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表 5 研究区开挖路基结构土层含盐量
Table 5. Salt content of subgrade soil in chaqia lake
路基
结构层取样深度/m Cl−/
（mol•kg−1）SO42−/
（mol•kg−1）离子比 含盐
量/%盐渍土类型 ① 0.2 2 1.13 0.89 0.55 A ② 0.4 1.6 0.55 1.44 0.52 A ③ 0.6 1.6 1.32 0.60 0.70 A 0.8 5.4 7.46 0.36 0.78 A ④ 1.0 6.2 10.37 0.30 0.71 A 1.2 145 50.08 1.45 1.57 A 1.4 39 34.77 0.56 0.74 B ⑤ 1.6 31.8 35.89 0.44 0.71 B 1.8 3.2 20.40 0.80 0.33 B ⑥ 2.0 62.1 43.67 0.71 1.00 B 2.2 89 48.28 0.92 1.19 B 2.4 17.4 14.11 0.62 0.32 B 2.6 83 48.29 0.86 1.17 B
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