The main purpose of this paper is the study of the pre-failure behaviour of loose vertical sand slopes stabilized by nailing system. In this research a series of centrifuge tests have been done and the behaviour of nailed vertical sand slopes has been traced in flight either by instrumentation or by image processing techniques.

By analyzing the behaviour curves of the nailed trenches, it can be inferred that some progressive failure surfaces are formed as the height of stabilized trench increases. During the formation of failure surfaces a kind of hardening is observed in the system, i.e. displacements remain constant or they increase with a lower rate after a sudden increment.