The Suoertou landslide

a giant old landslide with a volume of 72.85×106 m3 in Zhouqu county

Gansu province of China

has been reactivated with a small rate since 1970’s. The slow-moving character indicates the typical rheological behavior of the landslide. It is well known that mechanical characteristic of slip zone plays an important role in landslide activities. In order to clarify the creep behavior of slip zone and the relationship between long-term strength and residual strength

a series of directed creep shear tests under residual state is employed. It is found that the creep behavior of residual slip zone is strongly dependent on normal and shear stress

with two critical shear stresses and two critical initial strain rates. Moreover

it can be found that the critical shear stress and strain rate

when the creep develops into accelerated stage

have a linear relationship with normal stress separately. Based on the linear relationship between critical shear stress and normal stress

it can be speculated that the shear stress condition of the Suoertou landslide has been in accelerated creep state already. Meanwhile

the relationship between long-term strength and residual strength is analyzed and compared. It is found that long-term strength of the landslide’s slip zone is slightly greater than its residual strength

and the magnitude of their difference is negatively correlated with normal stress.