Analysis of a large-scale, stepped planar failure in the Central Andes uplands, Chile, using roughness profiles from terrestrial laser scanning

SEPÚLVEDA S.A; FUENTES J.P.; OPPIKOFER T.; HERMANNS R.L. ; MOREIRAS S.M.

Landslides and Engineered Slopes: Protecting Society through Improved Understanding

Taylor & Francis Group

Año: 2012; p. 1243 - 1247

Large volume rock slides and rock avalanches are common in the highlands of the Andesof central Chile and Argentina. Most of them have failed with a massive failure mode. An exception is a 0.7 km2 rock slide with a clear plane failure mode on two major steps found in the headers of the Maipo river drainage basin at the latitude of Santiago (33ºS). The failure surfaces were scanned with a terrestrial laser scanner, from which 35 high-resolution dip-slope topographic profiles were obtained. This information allowed computation of joint roughness of the shear surfaces, which along with Schmidt hammer field measurements allowed estimation of the joint shear strength and performing of limit equilibrium back-analyses. Deterministic and probabilistic analyses confirm that the block would be safe under static conditions, suggesting a seismic trigger. Pseudo-static analyses show that horizontal seismic coefficients between 0.4 and 0.7 would be necessary to induce the failure, depending on the amount of vertical acceleration. These results are in agreement with the presence of faults and shallow seismicity in the area and a nearby historic shallow crustal earthquake with peak acceleration estimates around 1 g. The results along with observations that subduction earthquakes do not produce such large accelerations in the areareinforce the hypothesis of crustal seismicity as a key factor for large landslide generation in the Andes highlands.