Abstract: To study the influence of water-soil chemical interaction on cohesive force under different conditions, montmorillonite- quartz remolded soil is prepared and soaked in ultrapure water (normal water), pH=3 HNO3 (acid rain) and pH=13.5 NaOH (alkaline waste liquid). The results show that, under the condition of ultrapure water, the cohesive force rises firstly and then declines and then rises again; under the acid condition, the cohesive force declines firstly and then rises and then declines again; under the alkaline condition, the cohesive force declines firstly and then rises and then declines again, at last rebounds. Temperature promotes the chemical reactions at different degrees. The X-ray diffraction analysis results show that acid causes corrosion to montmorillonite mineral. None of new material generated in montmorillonite sample during the soaking process leads to a decline in cohesive force. The reason for cohesive force rise in the middle stage of acid soaking is not clear. Under the alkaline condition, calcium silicate hydrate (CSH) is generated. Under the condition of ultrapure water, both CSH and CaCO3 are generated. The bond strength, connecting the unit cells through chemical bonds for the new ionic cements, is far greater than the strength of binding force connecting two adjacent montmorillonite layers. The presence of new cements cause rise of cohesive force under ultrapure water and alkaline conditions. Chemolysis and ion exchange are the main reasons for descent of cohesive force. Furthermore, combined with the vertical pressure of soil landslide and the internal friction angle, the shear strength variation of soil under the influence of water-soil chemical interaction is analyzed. Under the ultrapure water condition, the shear strength changes slightly in general; under the acid condition, the shear strength changes in accordance with the cohesive force; and under the alkaline condition, the shear strength increases in general.

Key words: montmorillonite, water-soil chemical interaction, cohesive force, calcium silicate hydrate