STUDY ON THE WATER SENSITIVITY CHARACTERISTICS OF THE SHEAR STRENGTH OF UNDISTURBED Q2 LOESS IN LANZHOU

Loess was seen as a kind of unique problematic soil around the world. Structural loess always embodies some very high water sensitivities which correlate closely with common engineering problems exiting in loess area. In this paper, a series of direct shear tests were utilized to study the relationships between peak strength, residual strength, ultimate strength, structural strength and water content and normal pressure for undisturbed Q2 loess with different moistures quantitatively. It could be concluded that peak strength of loess has the higher water sensitivity than its' residual and ultimate strength, and exponential function and linear function could be used to depict the relations between peak strength and water content and the relations between residual/ultimate strength and water content, respectively. The relationships between peak strength and water content can be normalized with respect to the maximal peak strength under various normal pressures, and exponential function is suited to describe the normalized relationships. In addition, there is an exponential correlation existing between structural strength and water content. For undisturbed Q2 loess, the shear strains under different normal pressures at failure are in the area of 1%~2% due to its' strong structural strength. Research findings obtained in the paper will be useful in the further comprehension and cognizance on the functioning mechanism and design criteria of shear strength of unsaturated structural loess.