Multidisciplinair Study of a Slow Creeping Landslide in South Spain

A multidisciplinary geophysical survey was carried out in Almargen (South Spain) in order to study a slow-creeping landslide affecting a major railway line. During the past fifty years several studies based on classical geotechnical methods have tried to understand and correct the creeping processes that pose an important hazard to the railway line. Part of these previous investigations included opening trenches, borehole drilling, installation of inclinometers and vibrating wire piezometers. As a result of these investigations a stabilization campaign based on the construction of a drainage system and cement injections was accomplished in 1999. The effects of the stabilization campaign were satisfactory until the spring of 2007 when several consecutive weeks of heavy rain occurred in the area. As a consequence, an increase in the rate of displacement was detected in several inclinometers located in the vicinity of the railway. The Spanish Railway Infrastructure Administration (ADIF) decided then to map in detail the subsurface of the affected areas with a detailed geophysical survey. The geophysical survey was concentrated along four lines (two above and below the railway) where P-wave seismic tomography, S-wave passive seismic (refraction microtremor) and electrical resistivity tomography (ERT) data were acquired.