The construction of a new access motorway to the city of Almeria, has involved the excavation of large cuttings half way up the mountain slope. The natural occurrence of rock block downfall (sizes ranging from 50 cm, to 6 m, approximately) has meant that certain block stabilization measures have had to be taken. This paper describes the methodology of the studies and the solutions developed.
Der Bau einer Autobahn fuer die Zufahrt in die Stadt von Almeria machte es notwendig, lange Einschni tte auf halber Höhe der Bergabhange vorzunehmen. Der natuerliche Steinschlag durch Ablösung von Felsblöcken und Geröll (von ca. 50 cm. bis 6 m Gröβe), hat es notwendig gemacht, Maβnahmen zur Stabilisierung von diesen Felsblöck en zu ergreifen. Diese Studie beschreibt die Methodik und die Lösungen, die hierzu entwickelt worden sind.
La construction d'un nouveau route d'access a la ville de Almeria, a origine des grandes excavations dans les montaignes proches. Les fenomènes d'inestabilite des bloques rocheuses (50 cm-6 m de diametre) a fait necessaire d'adopter des mesures extraordinaires pour assurer l'estabilisation de ces bloques. Ce communitation decrit la metodologie adopte pour obtenir la solution finale.
Owing to the proximity of the city of Almeria to the mountains, it has been necessary to excavate tunnels and deep cuttings as well as constructing large embankments, for the new access motorway to the city. The presence of buildings on the Aguadulce Slopes, whose axis runs parallel to the coast 'has served to restrict the available space. As a result, the road design has been split in two: one of the carriage ways runs through a tunnel excavated in the heart of the mountain, and the other has been constructed half way up the mountain slopes, by means of average-sized cuttings. Also, is necessary to reduce the risk of the inherently unstable blocks from falling down the slopes. Had the cuttings been any larger, such a risk would have been accentuated. Before the work started, it was already known that some of the blocks (up to 4 m, long), has broken loose from the upper part of the slope in recent years.
From a geological perspective, the Aguadulce slope is made up of Permotriassic materials from the Lujar or Gador mantle (forming part of the Alpujarride complex, a common formation in Granada and Almeria, in South-East Spain), and to be more specific, it consists of the upper dolomite-limestone layer of this mantle dating from the Mid or Upper Triassic. Two outcrops of this formation exist in the zone: a) A lower formation of calcium shales, originating from the Anisiense with occasional interlayering limestones and dolomites. b) A formation of dolomites overlying the former, and dating from the Ladiniense, with sporadic limestone interlayers. A diagram, indicating the geological units to be found there, can be seen in Fig. 1. This plan shows the potentially unstable rocky blocks, and these generally lie on the upper dolomitic cliff edge.
Initially, the zone has to be geologically and geotechnically mapped. The following methodology was devised: - Phase A) Use of aerial photography to define the slope topography. - Phase B) Geological mapping of the zone, based on topography, geological maps and some mechanical boring. - Phase C) A detailed definition of the rock blocks in the zone, on the basis of detailed photography with telephoto lenses. - Phase D) Schematization of block conditions for all those with sizes over 1 m3. Approximate size, potential undermining, existing fissures and joints, etc. - Phase E) Classification of the block typology into certain standard diagrams, on the basis of the kind of problem and solution: this classification is governed by the nature of the geology and the rocky dolomite structure that constitute the slope of the cliff edge. The classification established in Phase E), takes into account the fact that the blocks are often ledged or in columns connected to the cliff surface, owing to joint families running parallel to this surface.