The viscous creep component in shallow clayey soil and the influence of tree load on creep rates

Creep tests carried out on silty‐clay samples of a ‘terres noires colluvium’ show that even in shallow soils (1 m in depth) stress conditions can be high enough to initiate measurable creep displacements by the mechanism of continuous (viscous) creep. It is therefore not necessary to think exclusively of a shrink‐swell mechanism (seasonal creep) in order to explain these slow movements in the soil. The creep tests also show a negative correlation between effective normal stress and the viscosity of the soil material. Therefore in shallow soils removal of an external load (forest clearing) might increase the creep rate at lower slope angles and therefore decrease the stability of the slopes. At higher slope angles removal of external load decreases the creep rate.