The paper presents the description of behaviour of sandy soils subjected to relatively high hydraulic gradients based on experimental results. The influences of all major process, such as piping, suction elimination or preferential ways creations were tested. It describes the requirements on the new constitutive equation necessary for the description of the soils behaviour under certain conditions. The conclusions challenge some of the traditional points of view on the problems of soil degradation. All specimens have been obtained from the area of lately destructed buildings (due to problems with subsoil) or very close to it.