Influencing Factors Of Cohesive Clay On Dispersivityand Modification Of Dispersive Clay

Dispersive clay is a kind of promblematic soil being concered in the field of geotechnicalengineering. The cohensive force of dispersive clay decreases or even loses in the condition ofpurified water or water without much soluble salts, thus the soil particles which are oncetogether get into dispersive particles. It is serious that the dispersive clay threats the safety ofengineering. Though there has been a great process in the aspect of dispersive mechanism andtest methods, it is still not enough to be the guidance of the engineering in the field ofdispersive clay.The analysis of the influence of physical, chemical and mineral factors on dispersive claywere made based on the gray correlation analysis of gray system theory. Further study on theinfluence of Na+,pH and montmorillonite on dispersivity were did using the pinhole test andcrumb test. From what were obtained above, the effct of modification materials likeAlCl₃·6H₂O, MgCl₂·6H₂O, CaCl₂and CaO were studied. Finally, the conclusion of the paperwere certified by a engineering case.The main conclusions are as follows:（1） The sequence based on the association extent of all chemical, physical and mineralfactors affectting the dispersivity of clay was listed as follows: chemical indicators>mineralogical indicators and the physical indicators. The degree of association of pH andsodium content among all chemical indicators were relatively high.Further study with graysystem theory showed that there were two essential factors causing dispersivity of clay, that isthe high content of sodium ion and pH value.（2） The properties of montmorillonite with different ionic groups were greatly different.The expansion of Na-montmorillonite was obvious and Na-montmorillonite got the ability ofexpediting the dispersivity of clay, but the Ca-montmorillonite was opposite, it could preventdispersivity. The direct shear test showed that the soil cohesion of clayed soil would increaseand the friction angle would reduce with the increase content of montmorillonite.（3） The rules of chemical modification was proposed based on the dispersive mechanism.Dispersive clay could be modified with higher valence soluble salts. The reason was thatthickness of the diffusion layer would be reduced and the pH would go down since thesodium cations around soil particle surface could be replaced by cations with higher valencestate. （4）Those tests showed that the materials, such as AlCl₃·6H₂O, MgCl₂·6H₂O, CaCl₂andCaO could improve the ability of clay against erosion and change the the dispersive clay intonon-dispersive clay. The reasons were that the exist of Al_<sup>3+, Ca²⁺and Mg²⁺would take theplace of Na+around soil particals and pH would decrease so that the thickness of the diffusionlayer would decrease and the dispersivity of dispersive clay would be inhibited.