DOI: 10.5593/SGEM2016/B13/S05.067


Tuesday 6 September 2016 by Libadmin2016

References: 16th International Multidisciplinary Scientific GeoConference SGEM 2016, www.sgem.org, SGEM2016 Conference Proceedings, ISBN 978-619-7105-57-5 / ISSN 1314-2704, June 28 - July 6, 2016, Book1 Vol. 3, 529-536 pp

The paper describes a large landslide case produced in Breaza, Prahova District, which was investigated by geotechnical and geophysical methods in order to provide an appropriate solution for stabilization. Due to the fact that the area of the instability was inside of a golf club, the access of large drillings machines was prohibited and geoelectrical investigations proved to be a good mean of characterization of the main aspects of the slide (depth of shear surface, wet volumes). Over 60 soundings in Schlumberger configuration or profiling in Wenner configuration has been executed with a depth of investigation between 20m and 45m. This geophysical works provided vertical (transversal and longitudinal) pseudo-sections and several maps of apparent resistivity at different depths. The calibration of soundings was based on six geotechnical boreholes at maximum 10m depth, completed with geotechnical laboratory tests. Among them, the most useful have been few series of direct shear tests executed on soils with different moisture content, which allow estimating the decrease of shear parameters with an increase of moisture. The investigations revealed that the sliding mass consists in uncontrolled fills (without any engineering works of compaction or drainage) consisting of soft cohesive soils, disposed over the natural thin deluvium of the slope. The geological basement beneath these sliding deposits consists in a monocline structure which permanently supplies underground water transfer at the interface of the layers. Moreover, the geomorphological analyses of the terrain reveal that the area of the landslide represents in the meantime, the reception basin of the surface rain waters flows. Instability has been produced after two weeks of hard rain with over average quantities of precipitation and the next day after an earthquake with 6 magnitudes (on Richter scale). Considering the large scale of the landslide (over 1km length, 300m width and 12-15m depth of the shear surface) and the main cause of instability (the standing presence of excessive water content in sliding mass) the only feasible remedial measure was the construction of a superficial impermeable drain network, which proved to be over years an efficient tool for stabilization of the whole area.

Keywords: sliding mass, shear surface, sounding, direct shear.