Abstract: To mitigate the effect of frost heave, a countermeasure of fiberglass reinforced plastics (FRP) covering was put forward and applied to the foundation engineering of Qinghai-Tibetan transmission line. There is limited information involved in the mechanical properties of the interface between soil and FRP. A series of laboratory direct shear tests of the interface between silt and FRP plate are performed. The results show that the yield shear displacement is very small; and the interface shows short or no significant strain hardening stage. For frozen samples, the strength of the interface is drastically lost when the load reaches its critical strength. For unfrozen samples, the shear stress-displacement behavior of the interface is ductile failure and there is no obvious peak. The shear strength of the interface slowly decreases with the increase in water content for unfrozen samples. The strength of frozen sample increases with the increasing of negative absolute temperature and water content. Moreover, the temperature effect on the shear strength of the interface is more significant if soil water content is higher. When the soil water content is greater than 19%, the shear strength stabilized. The impact of temperature on the shear strength is mainly reflected in the change of cohesion. With the increasing of water content, temperature effects enhanced. The internal friction angle of the interface decreases with the increase in the absolute value of negative temperature and decreases with the increase of water content.

Key words: interface, direct shear test, shear strength, fiberglass reinforced plastics, Qinghai-Tibetan silt