Citation: | LIU Jiating, FU Yukai, LI Tonglu, ZHAO Chenxi, LI Ping, HOU Xiaokun, HU Xiangyang. Types of water film on the surface of loess and related mineral particles and their quantitative characterization[J]. Hydrogeology & Engineering Geology, 2022, 49(6): 105-113. doi: 10.16030/j.cnki.issn.1000-3665.202203049 |
The surface water film of fine particles in cohesive soil is an internal factor that affects the physical and mechanical properties of the soil. In the classical soil mechanics, the water film on the surface of soil particles is generally divided into two layers: strong bound water and weak bound water, i. e., the so-called electric double layer model. The existence of weak bound water is the reason for the plasticity of soil, thus, the plastic limit is the boundary moisture content of strong bound water and weak bound water. The model perfectly explains the consistency change and related physical and mechanical behavior of cohesive soil. However, through the isothermal adsorption test, it is found that there is an adsorbed water film on the surface of the soil particles, which has an important impact on the physical and mechanical properties of the unsaturated soil in the high suction section. Therefore, this paper divides the water film on the surface of soil into five types: monolayer adsorbed water, multi-layer adsorbed water, strong bound water, weak bound water and free water. The L2 loess specimen was taken from the topmost layer of Q2 in Zhengning of Gansu Province and are used to conduct isothermal adsorption test, liquid limit test and plastic limit test, respectively, to achieve the internal minerals that make up the loess and quantitative characterization of the types of water film on the particle surface.The soil-water characteristic curves (SWCC) of the loess specimen are tested. Combined with the above test results, the relationship between these boundary moisture contents and the matrix suction is defined on the SWCC. When the water vapor pressure is very low, the suction on the surface of the soil particles comes from the electrostatic attraction between the dipole molecules of water and the ions on the surface of the particles, forming a single layer of the adsorbed water, and the thickness of the water film is one water molecule diameter. In the place beyond the water molecular diameter from the particle surface, the suction comes from the van der Waals force, and the dipoles of water are oriented toward each other, forming multi-layer adsorbed water. When the moisture around the soil particles increases, the unbalanced molecular attraction on the surface of the particles can attract more polarized water molecules, the bound water is formed around the adsorbed water, which is divided into strong bound water and weak bound water. The water outside the adsorbed water and the bound water film is free water.
[1] | 李强,李同录,乔志甜,等. 非饱和土粒间毛细作用的微观不连续变形分析[J]. 工程地质学报,2021,29(3):834 − 842. [LI Qiang,LI Tonglu,QIAO Zhitian,et al. Microscopic discontinuity deformation analysis of capillary in unsaturated soil[J]. Journal of Engineering Geology,2021,29(3):834 − 842. (in Chinese with English abstract) doi: 10.13544/j.cnki.jeg.2020-140 |
[2] | 赵明华,刘小平,彭文祥. 水膜理论在非饱和土中吸力的应用研究[J]. 岩土力学,2007,28(7):1323 − 1327. [ZHAO Minghua,LIU Xiaoping,PENG Wenxiang. Application of aqueous film theory to study of unsaturated soil’s suction[J]. Rock and Soil Mechanics,2007,28(7):1323 − 1327. (in Chinese with English abstract) doi: 10.3969/j.issn.1000-7598.2007.07.007 |
[3] | 李广信. 高等土力学[M]. 北京: 清华大学出版社, 2004 LI Guangxin. Advanced Soil Mechanics[M]. Beijing: Tsinghua University Press, 2004. (in Chinese) |
[4] | LU N,ZHANG C. Soil sorptive potential:concept,theory,and verification[J]. Journal of Geotechnical and Geoenvironmental Engineering,2019,145(4):04019006. doi: 10.1061/(ASCE)GT.1943-5606.0002025 |
[5] | 曾立峰, 邵龙潭, 牛庚, 等. 考虑孔隙水微观赋存形态的非饱和粉土有效应力方程及其验证[J/OL]. 水文地质工程地质, (2022-03-09)[2022-03-21]. https://kns.cnki.net/kns8/DefaultResult/Index?dbcode ZENG Lifeng, SHAO Longtan, NIU Geng, et al. Effective Force Equation of Unsaturated Silt Soil Considering Microscopic Deposit Form of Pore Water and Its Verification[J/OL]. Hydrogeology and Engineering Geology, (2022-03-09)[2022-03-21]. (in Chinese with English abstract) |
[6] | 田慧会,韦昌富. 基于核磁共振技术的土体吸附水含量测试与分析[J]. 中国科学:技术科学,2014,44(3):295 − 305. [TIAN Huihui,WEI Changfu. A NMR-based testing and analysis of adsorbed water content[J]. Scientia Sinica (Technologica),2014,44(3):295 − 305. (in Chinese with English abstract) |
[7] | 何攀,许强,刘佳良,等. 基于核磁共振与氮吸附技术的黄土含盐量对结合水膜厚度的影响研究[J]. 水文地质工程地质,2020,47(5):142 − 149. [HE Pan,XU Qiang,LIU Jialiang,et al. An experimental study of the influence of loess salinity on combined water film thickness based on NMR and nitrogen adsorption technique[J]. Hydrogeology & Engineering Geology,2020,47(5):142 − 149. (in Chinese with English abstract) doi: 10.16030/j.cnki.issn.1000-3665.201910002 |
[8] | BAKER R,FRYDMAN S. Unsaturated soil mechanics:critical review of physical foundations[J]. Engineering Geology,2009,106(1/2):26 − 39. |
[9] | 王铁行,李彦龙,苏立君. 黄土表面吸附结合水的类型和界限划分[J]. 岩土工程学报,2014,36(5):942 − 948. [WANG Tiehang,LI Yanlong,SU Lijun. Types and boundaries of bound water on loess particle surface[J]. Chinese Journal of Geotechnical Engineering,2014,36(5):942 − 948. (in Chinese with English abstract) doi: 10.11779/CJGE201405019 |
[10] | 袁建滨. 粘土中结合水特性及其测试方法研究[D]. 广州: 华南理工大学, 2012 YUAN Jianbin. The study for properties of bound water on clayey soils and their quantitative methods[D]. Guangzhou: South China University of Technology, 2012. (in Chinese with English abstract) |
[11] | 张一敏. 球团理论与工艺[M]. 北京: 冶金工业出版社, 2002 ZHANG Yimin. Pellet theory and technology[M]. Beijing: Metallurgical Industry Press, 2002. (in Chinese) |
[12] | HABIBAGAHI K. Temperature effect and the concept of effective void ratio[J]. Indian Geotechnical Journal,1977,7(1):14 − 34. |
[13] | SKEMPTION A W,NORTHEY R D. The sensitivity of clays[J]. Géotechnique,1952,3(1):30 − 53. |
[14] | 李亚斌. 黄土及相关黏土矿物吸附结合水的定量研究[D]. 西安: 长安大学, 2018 LI Yabin. Quantitative study on the adsorption bound water of loess and related clay minerals[D]. Xi’an: Changan University, 2018. (in Chinese with English abstract) |
[15] | 张乃娴. 粘土矿物研究方法[M]. 北京: 科学出版社, 1990 ZHANG Naixian. Research methods of clay minerals[M]. Beijing: Science Press, 1990. (in Chinese) |
[16] | 中华人民共和国水利部. 土工试验规程: SL 237—1999[S]. 北京: 中国水利水电出版社, 1999 Ministry of Water Resources of the People’s Republic of China. Specification of soil test: SL 237—1999[S]. Beijing: China Water Power Press, 1999. (in Chinese) |
[17] | 李彦龙. 非饱和黄土结合水特性及水分迁移问题研究[D]. 西安: 西安建筑科技大学, 2015 LI Yanlong. Bound water properties and moisture migration in unsaturated loess[D]. Xi’an: Xi’an University of Architecture and Technology, 2015. (in Chinese with English abstract) |
[18] | ZHOU B C,LU N. Correlation between atterberg limits and soil adsorptive water[J]. Journal of Geotechnical and Geoenvironmental Engineering,2021,147(2):04020162. doi: 10.1061/(ASCE)GT.1943-5606.0002463 |
[19] | LANGMUIR I. The adsorption of gases on plane surfaces of glass,mica and platinum[J]. Journal of the American Chemical Society,1918,40(9):1361 − 1403. doi: 10.1021/ja02242a004 |
[20] | BRUNAUER S,EMMETT P H,TELLER E. Adsorption of gases in multimolecular layers[J]. Journal of the American Chemical Society,1938,60(2):309 − 319. doi: 10.1021/ja01269a023 |
[21] | LIKOS W J,LU N. Water vapor sorption behaviour of smectite-kaolinite mixtures[J]. Clays and Clay Minerals,2002,50(5):553 − 561. doi: 10.1346/000986002320679297 |
[22] | RIDLEY A M,DINEEN K,BURLAND J B,et al. Soil matrix suction:some examples of its measurement and application in geotechnical engineering[J]. Géotechnique,2003,53(2):241 − 253. |
[23] | 王竹溪. 热力学[M]. 北京: 高等教育出版社, 1955 WANG Zhuxi. Thermodynamics [M]. Beijing: Higher Education Press, 1955. (in Chinese) |
Types of water film around a soil particle (after Zhang Yimin[11])
X-ray diffraction pattern of the loess specimen
Particle size distribution curve of loess and its minerals
Isothermal adsorption curve of loess soil
Isothermal adsorption curve of non-clay minerals
Isothermal adsorption curve of clay minerals
Comparison of adsorption capacities of different minerals
Comparison of the measured adsorption moisture content of loess soil with the conversion results
Linear fit of the BET model
Boundary moisture content of various types of water film on SWCC of the loess sample