A new approach to rock slope stability – a probability classification (SSPC) R. Hack Æ D. Price Æ N. Rengers Abstract The newly developed system presented in this paper is based on a three-step approach and on the probabilistic assessment of independently dif- ferent failure mechanisms in a slope. First, the scheme classifies rock mass parameters in one or more exposures and allowance is made for weath- ering and excavation disturbance. This gives values for the parameters of importance to the mechanical behaviour of a slope in an imaginary, unweathered and undisturbed ‘reference’ rock mass. The third step is the assessment of the stability of the existing slope or any new slope in the reference rock mass, taking into account both method of excavation and future weathering. From the large quantity of data obtained in the field, the Slope Stability Probability Classification (SSPC) system has been proposed, based on the probabilities of different failure mechanisms occurring. Developed during 4 years of research in Falset, Tarragona province, Spain, it has been used with good results in Austria, South Africa, New Zealand and the Dutch Antilles. Re ´sume ´ Le nouveau syste `me de classification pre ´- sente ´ dans ce papier est base ´ sur une approche en trois e ´tapes et sur une e ´valuation probabiliste de diffe ´rents me ´canismes de rupture de pentes. D’abord, les parame `tres du massif rocheux sont mesure ´s sur un ou plusieurs affleurements, tout en conside ´rant les effets de l’alte ´ration et des pertur- bations du massif re ´sultant de l’excavation. Cette de ´marche permet ensuite d’obtenir les valeurs des parame `tres jouant un ro ˆle important dans le com- portement me ´canique d’une pente pour un massif rocheux non alte ´re ´ et non perturbe ´ par le processus d’excavation. La troisie `me e ´tape est l’e ´valuation de la stabilite ´ des pentes dans le massif rocheux de re ´fe ´- rence, prenant en compte a ` la fois la me ´thode d’excavation et l’alte ´ration future. A partir du nombre important de donne ´es obtenues sur le ter- rain, le syste `me de classification probabiliste de stabilite ´ des pentes (SSPC) a e ´te ´ propose ´, base ´ sur les probabilite ´s d’occurrence de diffe ´rents types de me ´canismes de rupture. De ´veloppe ´ pendant quatre ans a ` Falset, dans la province de Tarragone (Es- pagne), il a e ´te ´ utilise ´ avec de bons re ´sultats en Autriche, Afrique du Sud, Nouvelle Ze ´lande et aux Antilles ne ´erlandaises. Keywords Slope stability Æ Probability classification Æ SSPC Mots cle ´s Stabilite ´ des pentes Æ Me ´canismes de rupture de pente Æ Analyse probabiliste Æ SSPC Introduction In the last decades, knowledge of the behaviour of dis- continuous rock masses has developed tremendously. For constructions such as slopes, foundations and shallow tunnels, it has been recognized that discontinuities have a major influence on the mechanical properties of a rock mass. This perception has had consequences for the as- sessment of the engineering behaviour of a rock mass. Calculations for engineering structures in or on a rock mass must include discontinuity properties. Variations in properties can be considerable along the same disconti- nuity plane, however. As there may be hundreds of dis- continuities in a rock mass, each with its own variable properties, these, taken together with inhomogeneities in the rock material, require that in order to describe or D. Price is deceased. Received: 24 March 2001 / Accepted: 22 December 2001 Published online: 14 June 2002 ª Springer-Verlag 2002 R. Hack (&) Æ N. Rengers Section Engineering Geology, Centre for Technical Geosciences, International Institute for Aerospace Survey and Earth Sciences (ITC), Delft, The Netherlands e-mail: hack@itc.nl Tel.: +31-15-2748847 Fax: +31-15-2623961 D. Price Formerly at the Technical University, Delft, The Netherlands DOI 10.1007/s10064-002-0155-4 Bull Eng Geol Env (2003) 62:167–184 167