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Cut slopes failures on the Triassic beds in Coimbra, Portugal

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Abstract

An analysis is presented of several cut slope failures which occurred in the Triassic “Grés de Silves”, in the area of Areeiro in Coimbra, Portugal. They developed along thin mudstone layers dipping at some 16° towards the face of the excavation. The failures mainly occurred after periods of intense rainfall, sometimes immediately after the excavation of the slope, and in some cases have continued for the 7 years since, even where the slope height was only a few metres. The conditions leading to the failures were investigated in the field and in the laboratory. It was concluded that the main factors inducing the slope failure are a conjugation of the geological structure and the reduction in the shear strength of the mudstones when they dilate following excavation. This dilation allows the ingress of water further reducing the shear strength of the mudstones.

Résumé

Une analyse de plusieurs ruptures de talus de déblais, dans les «Grès de Silves» triasiques, dans le quartier d’Areeiro à Coimbra au Portugal, est présentée. Les ruptures se sont développées le long de couches argileuses de faible épaisseur plongeant à environ 16° vers le talus. Les ruptures sont survenues principalement après des périodes de pluies intenses, parfois immédiatement après l’excavation du déblai. Dans certains cas elles se sont poursuivies durant les sept années suivantes, même lorsque la hauteur du talus n’était que de quelques mètres. Les conditions à l’origine de ces ruptures de talus ont été étudiées sur le terrain et en laboratoire. Il a été conclu que les principaux facteurs responsables de ces ruptures de talus se trouvaient dans la structure géologique et la diminution de la résistance au cisaillement des argiles quand elles se dilatent après excavation, des fissures s’ouvrant alors et favorisant les infiltrations d’eau.

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Acknowledgments

This work was funded by the Portuguese Government through FCT – Fundação para a Ciência e a Tecnologia under the project PEst-OE/CTE/UI0073/2011 of the Geosciences Center.

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Authors and Affiliations

  1. Department of Earth Sciences, Geosciences Center, Largo Marquês de Pombal, University of Coimbra, 3000-272, Coimbra, Portugal

    Mário Quinta-Ferreira, Pedro Santarém Andrade & António Saraiva

  2. Department of Civil Engineering, Civil Engineering Center, Polo II, University of Coimbra, Rua Luis Reis dos Santos, 3030-788, Coimbra, Portugal

    Luís Lemos

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  1. Mário Quinta-Ferreira
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  2. Pedro Santarém Andrade
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  3. Luís Lemos
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  4. António Saraiva
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Correspondence to Mário Quinta-Ferreira.

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Quinta-Ferreira, M., Andrade, P.S., Lemos, L. et al. Cut slopes failures on the Triassic beds in Coimbra, Portugal. Bull Eng Geol Environ 72, 383–396 (2013). https://doi.org/10.1007/s10064-013-0483-6

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  • DOI: https://doi.org/10.1007/s10064-013-0483-6

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