Cutting D15: Stabilization of a large landslide in Marrakesh

Abstract

The D15 cutting is located on the Marrakesh-Agadir motorway, on the stretch between Imintanout and Argana, between kilometres 32 + 460 and 34 + 540 of the project. Measuring approximately 2,080mlong and with a maximumheight of almost 125 m, the D15 cutting was designed with 5-m wide berms every 10 m in height and a slope between berms of 1 H:2 V. The excavation of this cutting required moving more than 1.3Mm3 of earth, making it one of the biggest in the world. In late 2009, during the excavation of cuttingD15, superficial landslides were detected in the berms built so far. These phenomena of surface instability alerted the owners, represented by Autoroutes du Maroc (ADM), who hired the services of Eurogeotecnica-Euroconsult to study the problem. The preliminary study concludes that there was pathology in the cutting of greater significance than that referring to the surface landslide observed. The report highlighted the fact that it would not be possible to correct the latent effects simply with the surface treatments scheduled at that point by the contractor. These treatments consisted of a containment systembased on anchoring systems measuring less than 10 m in length, consolidated by means of a mesh of steel cables. In mid-march 2010 Eurogeotecnica-Euroconsult was contracted by ADM to begin exploration, monitoring and evaluating of the movements than had started, and to supervise the works carried out by the contractor. Following heavy rains, large fissures began to appear in the cutting in the excavation phase, in the berms themserves (following the stratification surfaces) ans behind the crown of the cutting. Subsequently, on 21 and 22 March 2010, a break of some depth ocurred in the southern end of the cutting in the excavation phase when two of the upper berms gave way and the colluviumthat covered that part of the slope shifted, with an approximate volume of 50,000m3.With regard to the notrhern part of the cutting, following the previous break, on the insistence of Eurogeotecnica- Euroconsult, elements were immediately installed that made it possible tomonitor the landslidemovements in the part of the rockmass,which were shown by the large fissures that appeared and that meant a more global movement than that initially supposed, thereby involving a volume of more than a million cubic metres. This landslide, while showing no evidence signs of acceleration, required immediate decisions to be taken in order to stabilize it. In light of the preliminary reports deriving from the supervision of the works in the cutting and the monitoring and evolution of the movements of the cutting in the northern part, ADM asked Eurogeotecnica-Euroconsult to study the problem, draw un the project and carry out general supervision of the cutting. This intervention was also carried out with technical advice on treating and managing the risks generated by landslides on the slope. © Springer-Verlag Berlin Heidelberg 2013.