Abstract: The instability of the cut slopes is a common geological hazard of the expressway under operation. Back pressure at the toe of the slope can quickly restrain the deformation of the potential landslide and ultimately improve the stability of the cut slope. However, the phenomenon that the horizontal deformation of the slope near the back pressure area does not converge in a short period of time often occurs, and reason that causing the sustained deformation is still unclear. Therefore, this paper presents the case history of a cut slope instability of an expressway at Station K46. The s of the slope instability and slope deformation induced by emergency remediations are evaluated. The results of the field survey and the theoretical analysis show that plugging of the seep holes leads to a poor drainage of groundwater, which is an important contribution factor to the slope instability. The traffic load on the top of the slope increases the driving force of the landslide, which leads to creep deformation of this cut slope.

Key words: Operation Period, Instability of Cut Slope, Back Pressure, Deformation Mechanism