Spatiotemporal evolution of the El Biar landslide (Algiers): new field observation data constrained by ground-penetrating radar investigations

A better understanding of the spatiotemporal evolution of landslides in urban zones is a key factor in assessing the risk of future slides within these areas. The El Biar landslide, located around the center of Algiers city, is one of the most important landslides in the region. It occurs mostly within a high strategic zone between schools, embassies and security buildings, thus causing a real risk for the population since it covers an area of 40 ha. The detection of various landslide-breaking surfaces leads to a better understanding of the mechanism of the spatiotemporal evolution of ground movement. In this work, we have combined two methods in order to provide strong evidence of its spatiotemporal evolution. The first method is based on field investigations to map old scarps related to the activity of the landslide. To better constrain our field investigations, most recent field observations were complemented by a second geophysical method using ground-penetrating radar with two different antennae which propagate under the two frequencies of 30 MHz and 100 MHz. As a result, we have reviewed this sliding area in detail and presented a new map of the whole affected zone. We have also delimited the affected zone by drawing a new map of the landslide. Combining field observations and the geophysical survey, we have highlighted the main discontinuity surfaces that lead us to suggest plausible realistic scenarios concerning the landslide’s evolution.