Rock slope failures occur in marble quarries existing in the Anticline of Estremoz (Alentejo, Southeastern of Portugal). The main geological and geo-mechanical features of the discontinuities and of the marble rock material are presented. The description of some accidents which occured in three quarries (Cerca de Santo António; Estremoz; Encostinha II, Borba; Encostinha, Borba) was used to explain the mechanisms of failure involved in the rock slope failures of the marble walls.


Dans les carrières de marble qui existent dans I'anticlinal de Estremoz (Alentejo, Sud-Ouest du Portugal) il y a des glissements de masses rocheuses. Les caracteristiques geologiques et geomecaniques plus importantes des discontinuites et du rocher sont ici presentees. La description des accidents qui ont eu lieu dans trois carrières (Cerca de Santo António, Estremoz; Encostinha II, Borba; Encostinha, Borba) a permit d'expliquer les mecanismes de rupture concernes avec les glissements des parois de marbre.


Das Abrutschen von Felsmassen kommt in Marmorbruechen in dem Antiklinale von Estremoz (Alentejo, Suedöstliches Portugal)vor. Es werden die wichtigsten geologischen und geomechanischen Merkmale der Diskontinuitat und des Marmorfelsmaterials dargestellt. Anhand der Beschreibung einiger Unfalle, die sich in 3 Steinbruechen ereigneten (Cerca deSanto António, Estremoz; Encostinha II, Borba; Encostinha, Borba) werden die Spaltmechanismen erklart, die das Abrutschen der Marmorwande verursachten.


Rock slope failures may occur in civil engineering works in mining and even in natural slopes. The most frequent are circular slidings, involving crushed and highly weathered rock, toppling, planar and wedge failures. To predict and to prevent these accidents it is required a convenient understanding of the mechanisms which are involved during the failure. Hence, it is appropriate to clearly define the geotechnical features of the rock mass (physical, geometrical, mechanical and hydraulical characteristics of the rock material and the discontinuities); and the characteristics of the accident (volume involved in the failure, the speed of the movement and the energy dissipated during sliding) and the factors which may explain it (weight and other loads, shear strength of the mobilized discontinuities, porewater pressure). Due to the mining conditions, several minor rock slope failures occur every year in the marble quarries which exist in the Anticline of Estremoz, Alentejo, the Southeastern region of Portugal (Fig. 1), and provide suitable information to study rock slidings. In this paper some of the major accidents are commented focusing the relevance of the features of the discontinuities which were involved and the mechanisms of failure which were observed.


Several high quality varieties of marble are quarried, near the towns of Estremoz, Borba and Vila Viçosa. Most of the extracted material is used in the internal market, but a very high percentage of the production is exported as blocks, plates, or tiles for buildings and other civil engineering works abroad. The marble formation is part of the anticline of Estremoz, which is a rather heterogeneous geological structure extending for about 40 km and striking NWSE. Besides marble layers, it is mainly composed by dolomite (90 % of the existing outcrops), and by schists, calcoschists and metavulcanites. The quarries with such features - small area and big depth - exist due to several factors: the swallow topography does not create conditions for a hillside quarry like in Carrara, Italy; the geological structure of the anticline enables an exploration technique by using subvertical walls which follow the discontinuities set and preferably the bedding planes ("corrume"); at the surface most of the outcropping rock mass is weathered, fractured, and carsified, with a thick earth topsoil and the good quality rock material only tends to appear at certain depth.

This content is only available via PDF.
You can access this article if you purchase or spend a download.