Experimental research on desorption curves of soil samples under different mineral compositions
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摘要: 精确测定土样含水率的数值对于研究高吸力时非饱和土的土水特性尤为重要。目前国内外现有土工规范在测定土样含水率时均设定恒温箱温度为110℃,鲜少有文献对该温度设定的合理性进行研究。利用同步热分析仪对高庙子膨润土、高岭土、台州滨海软黏土等7种不同类型的黏土进行了微商热重法分析（DTG）和热重分析（T-G）,同时对这7种黏土,用X射线衍射仪（XRD）测试了其矿物成分。试验结果显示随着土样中含蒙脱石矿物质量百分数的增加,其失去吸附水的温度越高；而当土样中不含蒙脱石矿物成分,土样的失去吸附水的温度比较低。认为对于蒙脱石含量较高的土样,测定含水率时,应将烘箱的温度由110℃提高150℃。Abstract: The accurate determination of water content for soils is particularly important for studying the soil-water characteristics of unsaturated soils with high suction range. At present, the oven temperature is set at 110℃ in the standards of soil testing method at home and abroad. Few literatures have studied the rationality of the temperature setting. Here, seven different types of clays, Na and Ca- Gaomiaozi bentonites, Shanghai soft clay, kaolin and Taizhou coastal soft clay, are analyzed by derivative thermogravimetry (DTG) and thermogravimetric analysis (T-G) with synchronous thermal analyzer. At the same time, their mineral compositions are tested by the X-ray diffraction (XRD). The test results show that the higher the mass percentage of montmorillonite minerals in soil samples, the higher the temperature of losing adsorbed water. When there is no montmorillonite mineral composition in soil samples, the temperature of losing adsorbed water is lower. It is considered that the oven temperature should be raised from 110 to 150 ℃ for measuring the water content of soil samples with high montmorillonite content.
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Keywords:
- soil-water retention behaviour /
- water content /
- hydration
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图 1 7种烘干土样去除背底的XRD
Figure 1. X-ray diffraction profiles of background subtracted for 7 samples drying at 105℃
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图 2 7种土样热重和微商热重法分析
Figure 2. Results of thermogravimetry and derivative thermo-gravimetry tests on seven clays
表 1 7种土样矿物成分和物理参数
Table 1 Physical properties and mineral compositions of seven samples
物化属性 台州滨海软土 上海软土 福建高岭土 广西红黏土 南阳膨胀土 GMZ07-Na[16] GMZ-Ca 液限/% 61.0 44.5[13] 48.1 77.8[14] 38.8[15] 276 99[18] 塑限/% 36.3 22.4[13] 30.7 42.1[14] 17.2[15] 37 41[18] 塑性指数 24.7 22.1[13] 17.4 35.7[14] 21.6[15] 239 58[18] 蒙脱石含量/% 1.0 — — 4.1 6.7 62 73~82[17] 伊利石含量/% 8.9 — — 3.2 3.6 — 1.0[17] 高岭石含量/% — — 92.2 56.8 4.4 — — 角闪石含量/% 1.1 0.9 — — 1.6 — — 绿泥石含量/% 13.0 17.6 — — — — — 石英含量/% 46.7 47.8 3.0 23.8 66.9 25 14~20[17] 长石含量/% 23.4 19.8 2.8 4.7 16.8 6 1~6[17] 云母含量/% — 11.2 2.0 — — — — 赤铁矿含量/% — — 7.4 — — — 方解石含量/% 2.6 1.3 — — — — — 白云石含量/% 3.3 — — — — — — 
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表 2 7种土样含水率对比
Table 2 Comparison of water content for seven samples
(%) 土样 w1 w2 w3 w2 -w1 w3 -w1 上海软土 2.06 2.32 2.52 0.26 0.46 福建高岭土 1.29 1.43 1.57 0.14 0.28 台州滨海软土 2.16 2.35 2.52 0.19 0.36 广西红黏土 2.72 3.42 3.93 0.70 1.21 南阳膨胀土 4.35 4.89 5.14 0.55 0.79 GMZ07-Na 3.81 4.42 4.59 0.61 0.78 GMZ-Ca 3.85 4.96 5.42 1.10 1.39 注： w1 ,w2 ,w3 分别为105℃,150℃,200℃计算得到的含水率。
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