Creep deformation until failure under constant water content in sandy model slope

The measurement of displacement on slopes under excavation or rainfall revealed that the displacement increased not only during excavation or rainfall but also afterward. The increase in displacement after stress loading can be identified as creep displacement under constant stress. However, the conditions for the generation of creep displacements are still unknown. To this end, inclined direct shear tests were conducted under constant stress and rainfall infiltration, and the measured data were analyzed to examine the conditions for creep displacement generation under rainfall infiltration. In some cases, shear displacement grew under constant volumetric water content (VWC) just prior to failure, but not in other cases. In the latter cases, shear displacement grew with increasing VWC. An accelerating increase in shear displacement just prior to failure—referred to as tertiary creep—could be observed in all cases in which shear displacement increased under constant VWC; meanwhile, a decelerating increase in shear displacement just after the start of the constant VWC duration—referred to as primary creep—could not be observed in some cases. The creep displacement normalized by all shear displacements until failure was larger when the increase in VWC corresponding to the shear displacement during soil absorption was greater. Thus, a larger increase in VWC corresponding to shear displacement during the absorption process is a condition for the generation of creep displacement under constant VWC. Primary creep displacement developed under the condition of no normal displacement, indicating a steady state in the shear zone. The primary creep displacement was greater for cases with a higher initial velocity at the start of the constant VWC duration. Thus, the absence of an increase in normal displacement under constant VWC may be a condition for the generation of primary creep, and a larger primary creep might be generated with a larger initial displacement velocity at the start of the constant VWC duration. The relationships between velocity and acceleration derived from the measured shear displacement during both the primary and tertiary creep stages are identical and linear on a logarithmic scale for each case. A future study will establish methods for predicting creep shear displacement based on the simple relationships between the velocity and acceleration derived from the measured displacement.