Experimental study on soil-water characteristic curves of sandy loess
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摘要: 针对取自浩吉铁路阳城隧道的砂质黄土土样,采用张力计法、滤纸法和露点水势仪(WP4C)法,得到了宽广吸力范围内不同干密度砂质黄土的土-水特征曲线(SWCC)。采用van Genuchten模型对SWCC试验结果进行拟合,确定其进气值。基于扫描电镜试验,对不同干密度和含水率砂质黄土的微观孔隙结构进行了观测,从宏微观角度分析了不同干密度土样SWCC的初始饱和含水率、失水速率以及进气值的变化规律。试验结果表明:砂质黄土的体积含水率随基质吸力的增加逐渐减小;随着干密度增加,土体内部的孔隙结构由较多的架空孔隙转化为较均匀的中等孔隙,初始饱和含水率和失水速率逐渐降低,进气值逐渐增大。Abstract: A series of laboratory tests are conducted on sandy loess taken from Yangcheng Tunnel of Haoji Railway under different dry densities by the combination of tensiometer method, filter paper method, and dew point hydro potential meter (WP4C) method. The soil-water characteristic curve (SWCC) of sandy loess in a wide suction range is obtained, and the effect of the initial dry density is emphatically studied. The van Genuchten model is used to fit the SWCC test results under different dry densities and the air entry value of the SWCC is determined. The microscopic pore structure of sandy loess with different dry densities and water contents is studied by scanning electron microscope tests. The change rules of the initial saturated water content, water loss rate and air entry value of SWCC under different dry densities are observated from a macro-micro perspective. The test results show that the volumetric water content of sandy loess decreases with the increase of matric suction, and the pore structure of soil changes from more overhead pores to more uniform medium pores with the increase of dry density. The initial saturated water content and water loss rate gradually decrease, and the air entry value gradually increases.
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Keywords:
- unsaturated soil /
- wide suction range /
- sandy loess /
- soil-water characteristic curve /
- dry density
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表 1 砂质黄土的基本物理参数
Table 1 Basic physical parameters of sandy loess
颗粒相对密度Gs 液限wL/% 塑限wP/% 塑性指数IP 最优含水率wop/% 最大干密度 γd,max/ (g·cm-3)2.70 24.0 12.8 11.2 12.0 1.81 表 2 SWCC模型拟合参数
Table 2 Fitting parameters for SWCC models
SWCC模型 参数1 参数2 参数3 R2 Gardner模型 9.409 0.791 — 0.984 van Genuchten模型 0.852 2.655 0.148 0.985 Fredlund-Xing模型 2.986 1.256 1.236 0.997 表 3 van Genuchten模型拟合参数
Table 3 Fitting parameters for van Genuchten model
干密度/(g·cm-3) 参数1 参数2 参数3 R2 1.40 0.852 2.655 0.148 0.9846 1.55 0.602 2.040 0.176 0.9930 1.65 0.118 1.229 0.410 0.9897 -
[1] 陈正汉, 谢定义, 王永胜. 非饱和土的水气运动规律及其工程性质研究[J]. 岩土工程学报, 1993, 15(3): 9-20. https://www.cnki.com.cn/Article/CJFDTOTAL-YTGC199303001.htm CHEN Zheng-han, XIE Ding-yi, WANG Yong-sheng. Experimental studies of laws of fluid motion, suction and pore pressures in unsaturated soil[J]. Chinese Journal of Geotechnical Engineering, 1993, 15(3): 9-20. (in Chinese) https://www.cnki.com.cn/Article/CJFDTOTAL-YTGC199303001.htm
[2] 蔡国庆, 赵成刚, 刘艳, 等. 非饱和土土-水特征曲线的温度效应[J]. 岩土力学, 2010, 31(4): 1055-1060. doi: 10.3969/j.issn.1000-7598.2010.04.008 CAI Guo-qing, ZHAO Cheng-gang, LIU Yan, et al. Temperature effects on soil-water characteristic curve of unsaturated soils[J]. Rock and Soil Mechanics, 2010, 31(4): 1055-1060. (in Chinese) doi: 10.3969/j.issn.1000-7598.2010.04.008
[3] 蔡国庆, 张策, 李舰, 等. 考虑初始干密度影响的SWCC预测方法研究[J]. 岩土工程学报, 2018, 40(增刊2): 27-31. https://www.cnki.com.cn/Article/CJFDTOTAL-YTGC2018S2008.htm CAI Guo-qing, ZHANG Ce, LI Jian, et al. Prediction method for SWCC considering initial dry density[J]. Chinese Journal of Geotechnical Engineering, 2018, 40(S2): 27-31. (in Chinese) https://www.cnki.com.cn/Article/CJFDTOTAL-YTGC2018S2008.htm
[4] 蔡国庆, 盛岱超, 周安楠. 考虑初始孔隙比影响的非饱和土相对渗透系数方程[J]. 岩土工程学报, 2013, 36(5): 827-835. https://www.cnki.com.cn/Article/CJFDTOTAL-YTGC201405006.htm CAI Guo-qing, SHENG Dai-chao, ZHOU An-nan. Approach for predicting the relative coefficient of permeability of unsaturated soils with different initial void ratios[J]. Chinese Journal of Geotechnical Engineering, 2013, 36(5): 827-835. (in Chinese) https://www.cnki.com.cn/Article/CJFDTOTAL-YTGC201405006.htm
[5] 张雪东, 赵成刚, 蔡国庆, 等. 土体密实状态对土-水特征曲线影响规律研究[J]. 岩土力学, 2010, 31(5): 123-128. https://www.cnki.com.cn/Article/CJFDTOTAL-YTLX201005025.htm ZHANG Xue-dong, ZHAO Cheng-gang, CAI Guo-qing, et al. Research on influence of soil density on soil-water characteristic curve[J]. Rock and Soil Mechanics, 2010, 31(5): 123-128. (in Chinese) https://www.cnki.com.cn/Article/CJFDTOTAL-YTLX201005025.htm
[6] 马田田, 韦昌富, 陈盼, 等. NaCl溶液对土体持水特性影响的试验研究[J]. 岩土力学, 2015, 36(10): 2831-2836. https://www.cnki.com.cn/Article/CJFDTOTAL-YTLX201510013.htm MA Tian-tian, WEI Chang-fu, CHEN Pan, et al. An experimental study of effect of NaCl solution on soil water characteristics[J]. Rock and Soil Mechanics, 2015, 36(10): 2831-2836. (in Chinese) https://www.cnki.com.cn/Article/CJFDTOTAL-YTLX201510013.htm
[7] 高游, 孙德安, 张俊然, 等. 考虑孔隙比和水力路径影响的非饱和土土水特性研究[J]. 岩土工程学报, 2019, 41(12): 2191-2196. https://www.cnki.com.cn/Article/CJFDTOTAL-YTGC201912006.htm GAO You, SUN De-an, ZHANG Jun-ran, et al. Soil-water characteristics of unsaturated soils considering initial void ratio and hydraulic path[J]. Chinese Journal of Rock Mechanics and Engineering, 2019, 41(12): 2191-2196. (in Chinese) https://www.cnki.com.cn/Article/CJFDTOTAL-YTGC201912006.htm
[8] 赵天宇, 王锦芳. 考虑密度与干湿循环影响的黄土土水特征曲线[J]. 中南大学学报(自然科学版), 2012, 43(6): 2445-2453. https://www.cnki.com.cn/Article/CJFDTOTAL-ZNGD201206062.htm ZHAO Tian-yu, WANG Jin-fang. Soil-water characteristic curve for unsaturated loess soil considering density and wetting-drying cycle effects[J]. Journal of Central South University (Science and Technology), 2012, 43(6): 2445-2453. (in Chinese) https://www.cnki.com.cn/Article/CJFDTOTAL-ZNGD201206062.htm
[9] TOMBOLATO S, TARANTINO A. Coupling of hydraulic and mechanical behaviour in unsaturated compacted clay[J]. Géotechnique, 2005, 55(4): 307-317.
[10] YANG H, RAHARDJO H, LEONG E C, et al. Factors affecting drying and wetting soil-water characteristic curves of sandy soils[J]. Canadian Geotechnical Journal, 2004, 41(5): 908-920.
[11] GALLAGE C P K, UCHIMURA T. Effects of dry density and grain size distribution on soil-water characteristic curves of sandy soils[J]. Soils and Foundations, 2010, 50(1): 161-172.
[12] 杨雨. 水-力耦合作用下非饱和土渗流特性演化规律的试验研究[D]. 北京: 北京交通大学, 2019. YANG Yu. Experimental Investigation on Water Permeability of Unsaturated Soils under Hydrro-Me Coupled Conditions[D]. Beijing: Beijing Jiaotong University, 2019. (in Chinese)
[13] GARDNER W R. Some steady state solutions of the unsaturated moisture flow equation with application to evaporation from a water table[J]. Soil Science, 1958, 85: 228-232.
[14] VAN GENUCHTEN M T. A closed-form equation for predicting the hydraulic conductivity of unsaturated soils[J]. Soil Science Society of America Journal, 1980, 44(5): 892-898.
[15] FREDLUND D G, XING A. Equations for the soil-water characteristic curve[J]. Canadian Geotechnical Journal, 1994, 31(4): 521-532.
[16] GENUCHTEN M T V, NIELSEN D R. On describing and predicting the hydraulic properties of unsaturated soil[J]. Annales Geophysicae, 1985, 3(5): 615-628.
[17] 熊承仁, 刘宝琛, 张家生. 重塑黏性土的基质吸力与土水分及密度状态的关系[J]. 岩石力学与工程学报, 2005, 24(2): 321-327. https://www.cnki.com.cn/Article/CJFDTOTAL-YSLX20050200R.htm XIONG Cheng-ren, LIU Bao-chen, ZHANG Jia-sheng. Relation of matric suction with moisture state and density state of remolded cohesive soil[J]. Chinese Journal of Rock Mechanics and Engineering, 2005, 24(2): 321-327. (in Chinese) https://www.cnki.com.cn/Article/CJFDTOTAL-YSLX20050200R.htm