Study On Highway Engineering Characteristic Of Expansive Soils And Its Calamity Prevention And Cure Technology

With the research object of expansive soil in both supported projects(Guangxi Nanyou Highway, Bailuo Highway, Nanning high-speed cycling track, Hubei Dangyijing Highway)and representative expansive soils regions, focused on the highway engineering property, the technology of the highway investigation and design have been researched, the classification system on highway expensive soils has been given, and the technology of Cohesive Non swelling soil coverage(CNS) has also been studied by a series of In-situ investigation, laboratory test, numerical simulation, theoretical analysis and engineering examples. It has a great significance to the development of the highway in expensive soil regions. The research achievements are as follow:1. Comprehensive, extensive laboratory testing experiments and in-situ tests have been put on both mechanic and chemistry properties of expensive soils. including X ray scattering method which definite the mineral composing and the space of the montmorillonite layers, the mercury intrusion porosimetry method which definite the relatively large pore size distributing, the granule analysis method which definite the distributing of the expensive soil granules. On such basis, the fractal rule of expensive soils and characteristic rules between soil– water characteristic curve of soil and pore size distributing have been studied. By conducting the In-situ competitive experiment, an estimate methods of bearing capacity of expansive soils ground have been given.2. Discussed the practice and theory of Atterberg's limits identification on the expensive soil, especially studied the Standard moisture absorption water content (SMA). It had been discovered that there are linear relations between the content of montmorillonite, specific surface area (SSA) and CEC. A new classification standard use SMA as classification index has been put forward.3. The cracking behavior due to surface evaporation flux and the methods of quantitative analysis of crack depth are systemically been studied. By using the three dimension expansive device developed by the research team, three dimension expansive tests are conducted. The result shows that: the swelling pressures of expensive soil in three dimensions are different. Most of the samples shows that the vertical pressures are bigger than horizontal pressures, the ratio of the two were between 0.69～4.3. Volume shrinkage index of expensive soils had a good relative relation with their taxonomic organization. Volume shrinkage index of high expansive clays is larger than 0.025 roughly, the mid-expansive soil is between 0.021~0.025 and the weak expansive soils is approximately less than 0.021. Three ideal methods are used to determine the value of volume changes of expansive soils exist. These are described as heave predictions based on oedometer tests, soils suction tests, and shrinkage tests.4. An integrity engineering classification system of highway expansive soils is developed. These include subgrade filling, ground, slope and field classification standards, which have significant meaning for choice of highway field and treated method of expansive soils.5. Put some experimental research on Cohesive Non Swelling Soil coverage technology, confirmed the influence of protection layer on expensive soil. Put forward the design and construction method for expensive soil slope and foundation protection.