Scholarly record

APPLICATION OF ROCK MASS RATING AND SLOPE MASS RATING IN SLOPES OF CENTRAL PORTUGAL

Pedro Santarém Andrade

Abstract

This paper presents a study on the stability of nineteen excavation slopes in metamorphic and carbonate rock masses along roads and urban areas in Central Portugal. The slopes studied are formed by phyllites intercalated by metagreywackes belonging to the Xisto-Grauvaquico Complex; quartzites and limestones of the Bussaco Ordovician-Silurian synclinal; schists of the Crystallophyllic Complex; and limestones and dolomites of Jurassic age. Road safety and urban areas are threatened by stability problems. In the assessment of the slopes behaviour the presence of groundwater is an important parameter. The occurrence of rock slopes movements is usually linked to periods of intense rainfall. A geologic survey and characterization of discontinuity parameters such as orientation, spacing, persistence, aperture, roughness, filling and weathering were carried out, focussing specifically on the development of stress cracks, and the slope movements. The Slope Mass Rating system is implemented to identify the possible instability situations and their severity, and to indicate possible support measures. Landslides occurring in 56 sections of nineteen slopes were identified. The most frequent instability situations were rock blocks falls, wedge, toppling and translational failures. Slopes were studied using the original Slope Mass Rating system with modifications related to the wedges failures identified. The results of the modified Slope Mass Rating approach lead to a more accurate evaluation of potential instability of the slope sections where the wedges failures occurred.

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