Collapse behaviours due to soaking under constant stress direct shearing for an unsaturated statically compacted soil are investigated with water content and matric suction measurement. Especially, the effect of the stress and soaking history on the compressible and shear behaviour under constant vertical stress are investigated by using a new developed direct box shear apparatus with water content and matric suction measurement. An electrical sensors for water content measurement is located near the shear plane, getting closely relationship between shear stress, normal stress and water content at shear zone under soaking condition. Experimental data obtained are compared with the results predicted by a semi-empirical relationship as a function of changes in water contents and vertical stresses under soaking, in which the ability of the model is confirmed through the comparison with the experimental results. Copyright ASCE 2006.