DOI: 10.5593/sgem2017/12/S02.061


S. Alija, M. Quinta-Ferreira, F.J. Torrijo, R. Arroyo
Sunday 10 September 2017 by Libadmin2017

References: 17th International Multidisciplinary Scientific GeoConference SGEM 2017, www.sgem.org, SGEM2017 Conference Proceedings, ISBN 978-619-7105-99-5 / ISSN 1314-2704, 29 June - 5 July, 2017, Vol. 17, Issue 12, 477-484 pp, DOI: 10.5593/sgem2017/12/S02.061


A case study concerning a drystone retaining wall that failed during construction, is presented. The site geology, the materials and their geotechnical characteristics are documented and discussed. The detailed site investigation performed allowed to define three geotechnical units: 1 - anthropogenic deposits; 2 - quaternary alluvial and colluvial deposits; 3 - Neogene alluvial fan. The third geotechnical unit, the Neogene alluvial fan, is mainly composed by dense and very dense sands, showed the best geotechnical properties and was used as foundation, as well as fill material. The results of the study allow to understand and emphasize the importance of the properties of the foundation ground and of the backfill of the drystone retaining wall to obtain stability for the structure. The main errors, solutions, conclusions and recommendations are presented, in order to prevent problems in similar construction works. The retrospective analysis concluded that several linked mistakes during construction caused the collapse of the drystone retaining wall namely the lack of adequate drainage, loose compactness of the fill, unsuitable backfill material and bad construction technique of the drystone retaining wall using of only one row of blocks and a wrong layout of the stone blocks aligned in columns and lines. With heavy rain conditions, an increase in the weight of the backfill and a decrease of its geotechnical parameters occurred, reducing the wall’s stability. The lack of adequate drainage facilitated the formation of gullies in the fill. These construction errors reduced significantly the safety factor and caused the failure. When substantial changes are to be incorporated compared to the established standards it is always necessary to previously validate those changes using well known design methods.

Keywords: Drystone Retaining Wall, Slope Stability, Backfill, Wall Failure