The Swelling And Shrinking Mechanism And Modification Of Montmorillonite

The mineral of expansive soil is mostly.composed of montmorillonite, illite, kaolinite or mixxing layer of montmorillonite-illite compound. The hydrophilicity of illite and kaolinite is only as about 1/10 and 1/60 as that of montmorillonite. So the content of montmorillonite mainly affects the capability of swelling and shrinking of expansive soil. Montmorillonite is made up of two layers of silicon oxygen tetrahedron, and one inserted layer of aluminium (magnesium) oxygen octahedral, forming a 2:1 type layered silicate mineral. Insertion of cations between the layers of montmorillonite results in several times of expanding rate after the absorption of water in c axis direction.In this paper, Ca(OH)₂ and CaCl₂ are choosed as the modifier to change the montmorillonite's swelling capability after summarizing the former researches. The influences of compound and amount of Ca²⁺ on the swelling and cation exchangeable capacity of montmorillonite were discussed by comparing the properties,microstructures of montmorillonite and granularity analysis before and after modification. The stability of montmorillonite was investigated by the analysis of the swelling highness, swelling capacity and exchangeable calcium capacity after modification by dry circulation, wet circulation and wet-drying circulation.Results show that both raw montmorillonite and Na-montmorillonite have lower swelling capacity after modified by Ca²⁺, but the reducing extent of modified raw montmorillonite is larger than that of modified Na- montmorillonite. The montmorillonite shows smaller swelling capacity, lower exchangeable calcium and compact microstructure when it was modified by 8% CaCl₂. After experienced by dry circulation, wet circulation and wet-drying circulation, the swelling highness, swelling capacity and exchangeable calcium capacity of modified montmorillonite changed. The stability of modified montmorillonite after the climatic change, has the order of wet-drying circulation＞wet circulation＞dry circulation.Based on the project of the west transportation construction, the samples of expansive soil of the Nan-You Highway's 133.78 kilometer in Guangxi province were selected along the different depth for characterizing the capability of swelling and shrinking. By the analysis of chemical compositions, particle size and DSC, the geological engineering characteristics of the expansive soil were discussed, which is important for the modification and stabilization of montmorillonite.