Black cotton soil in East Africa is not a stable engineering material for highway and railroad projects. Its strong swelling potential when it absorbs water causes distresses in subgrade of highway and railroad, and t...Black cotton soil in East Africa is not a stable engineering material for highway and railroad projects. Its strong swelling potential when it absorbs water causes distresses in subgrade of highway and railroad, and thus leads to failures of the projects. This paper presents study on the swelling characteristics of black cotton soil in East Africa. Lab tests were conducted to obtain its basic engineering properties, and the results show that black cotton soil contains high amount of montmorillonite and exchangeable cations and is strong expansive soil. Molecular modelling was exploited to further investigate water absorption ability of montmorillonite. Three different molecular models of montmorillonite were constructed and used for simulations, among which Types I and II montmorillonite represent the expansive soil montmorillonite in China, and Types II and III montmorillonite represent black cotton soil montmorillonite in East Africa. The results showed that the interlayer cations of Type III montmorillonite possessed the strongest water absorption ability based on analysis of radial distribution function(RDF) of cations. Interlayer compensatory cations of Na+ enhance the hydration ability of the other major cations, thus resulting in the strong swelling potential of East-Africa black cotton soil.展开更多
This paper presents a study research in the laboratory of three clayey soils from the depression of the Lama, a tropical climate area where disorders appear on construction and roads. Samples were tested to establish ...This paper presents a study research in the laboratory of three clayey soils from the depression of the Lama, a tropical climate area where disorders appear on construction and roads. Samples were tested to establish the relationship between their mineralogy and their geotechnical properties. On the three clayey soils, analyses were performed to characterize the macroscopic behavior (physical tests, free swelling test and compressibility tests) and the microstructural, chemical and mineralogical characterizations by thermal analysis, chemical analysis, X-Ray diffraction, Scanning Electron Microscopy observations complementary X-ray EDS analyses. At first glance, the results of physical and compressibility tests appear not to be consistent with the free swelling test results. Indeed, these results highlighted differences in the behaviors of the samples because the swelling potential revealed by the results of physical and compressibility test does not follow the same trend as the one given by the free swelling test result. The main clay minerals in the studied clayey soils varied from fibrous clays (palygorskite) to best-known clays such as smectite and kaolinite. Microstructural, chemical and mineralogical analyses allowed to understand and explain the different trends obtained by the different types of geotechnical characterization tests of studied clayey soils.展开更多
基金Project(51878164) supported by the National Natural Science Foundation of ChinaProjects(BK20180149, BK20161421) supported by the Natural Science Foundation of Jiangsu Province, ChinaProject(KFJ170106) supported by Changsha University of Science & Technology via Open Fund of National Engineering Laboratory of Highway Maintenance Technology, China。
文摘Black cotton soil in East Africa is not a stable engineering material for highway and railroad projects. Its strong swelling potential when it absorbs water causes distresses in subgrade of highway and railroad, and thus leads to failures of the projects. This paper presents study on the swelling characteristics of black cotton soil in East Africa. Lab tests were conducted to obtain its basic engineering properties, and the results show that black cotton soil contains high amount of montmorillonite and exchangeable cations and is strong expansive soil. Molecular modelling was exploited to further investigate water absorption ability of montmorillonite. Three different molecular models of montmorillonite were constructed and used for simulations, among which Types I and II montmorillonite represent the expansive soil montmorillonite in China, and Types II and III montmorillonite represent black cotton soil montmorillonite in East Africa. The results showed that the interlayer cations of Type III montmorillonite possessed the strongest water absorption ability based on analysis of radial distribution function(RDF) of cations. Interlayer compensatory cations of Na+ enhance the hydration ability of the other major cations, thus resulting in the strong swelling potential of East-Africa black cotton soil.
文摘This paper presents a study research in the laboratory of three clayey soils from the depression of the Lama, a tropical climate area where disorders appear on construction and roads. Samples were tested to establish the relationship between their mineralogy and their geotechnical properties. On the three clayey soils, analyses were performed to characterize the macroscopic behavior (physical tests, free swelling test and compressibility tests) and the microstructural, chemical and mineralogical characterizations by thermal analysis, chemical analysis, X-Ray diffraction, Scanning Electron Microscopy observations complementary X-ray EDS analyses. At first glance, the results of physical and compressibility tests appear not to be consistent with the free swelling test results. Indeed, these results highlighted differences in the behaviors of the samples because the swelling potential revealed by the results of physical and compressibility test does not follow the same trend as the one given by the free swelling test result. The main clay minerals in the studied clayey soils varied from fibrous clays (palygorskite) to best-known clays such as smectite and kaolinite. Microstructural, chemical and mineralogical analyses allowed to understand and explain the different trends obtained by the different types of geotechnical characterization tests of studied clayey soils.
