Abstract: Surfactants can entry into soil and ground water environment through a number of ways, such as industrial, agricultural and daily activities, and thus lead to environment pollution and the change of soil behaviour. Silty soils are separately modified with anionic surfactant sodium dodecyl benzene sulfonate (SDBS) and cationic surfactant cetrimonium bromide(CTAB), then the strengths of modified silty soils are investigated. The internal friction angle become small when modify by surfactants, and the internal friction angle turn to be more and much smaller as increasing the concentration of surfactants. When the concentration of surfactants reached 2%, the internal friction angle of silty soil decreased approximately by 23.9%. The cohesion decreased by 91.8% when adding 2% SDBS to silty soil, namely, the cohesion of SDBS modified silty soil decrease quite a bit, while that of CTAB modified silty soil increase, and the maximum growth rate is 41.8%. The solution pH have a very slight effect on the internal friction of modified silty soil, while the cohesion of surfactants modified silty soil tend to decline as increasing pH. The change of pH can lead to the change of electric charge on soil surface, resulting in changes of electrostatic interaction between soil particles, and influencing the cohesion of silty soils.

Key words: surfactant, modified silty soil, shear strength, cohesion, internal friction angle