The check of the stability of banks towards the slidings always crosses by the adoption of empirical global safety factors result, generally, of the study of the break along the deep surface of sliding. The mechanical model suited to this mode of break is subject to controversy. In this article we propose a mechanical model of calculation for the break along the deep surface of sliding based on the kinematic method of the stiff solids (limit analysis). A comparison of this model proposed with the conventional model was led according to the statico-probability concept of security. The reliability of the system is expressed by means of the indication of reliability β.