iEMSs 2008: International Congress on Environmental Modelling and Software Integrating Sciences and Information Technology for Environmental Assessment and Decision Making 4 th Biennial Meeting of iEMSs, http://www.iemss.org/iemss2008/index.php?n=Main.Proceedings M. Sànchez-Marrè, J. Béjar, J. Comas, A. Rizzoli and G. Guariso (Eds.) International Environmental Modelling and Software Society (iEMSs), 2008 Early warning of fast landslides triggering based on instrumented slope data analysis Emilia Damiano a , Roberto Greco a,b , Andrea Guida a and Lucio Olivares a,b a Dipartimento di Ingegneria Civile, Seconda Università di Napoli, via Roma 29 – 81031 Aversa (CE), Italy (roberto.greco@unina2.it) b CIRIAM – Centro Interdipartimentale di Ricerca in Ingegneria Ambientale, Seconda Università di Napoli, via Roma 29 – 81031 Aversa (CE), Italy Abstract: The results of laboratory infiltration experiments on instrumented small scale model slopes are presented. Loose granular pyroclastic soils from the mountainous area north-eastern of Napoli have been examined. The experiments aimed to reproduce the simple case of a homogeneous indefinite slope, for a better understanding of the hydraulic processes leading to slope failure. With this respect, useful information was provided by the results of coupled measurements of soil suction and volumetric water content, respectively carried out by minitensiometers and Time Domain Reflectometry. The obtained results indeed showed how soil wetting during rainfall infiltration took place under matric suction values around 5kPa smaller than what could be predicted by equilibrium water retention curves estimated in laboratory. Since steep slopes equilibrium is often guaranteed by cohesion increment due to suction under unsaturated conditions, the obtained result indicates that effective early warning of fast landslides should rely on direct monitoring of soil suction and water content in the field. Keywords: Flowslides; Pyroclastic granular soils; Physical modelling; TDR; Early warning. 1. INTRODUCTION Occurrence of fast landslides has become more and more dangerous during the last decades, due to the increased density of settlements, industrial plants and infrastructures. Such problem is particularly worrying in Campania (Southern Italy), where the fast population growth led a diffuse building activity without planning: indeed, recent flowslides caused hundreds of victims and heavy damages to buildings, roads and other infrastructures. Large mountainous areas in Campania are mantled by loose pyroclastic granular soils up to a depth of a few meters from top soil surface. These soils have usually a grain size that falls in the domain of silty sands, including pumice interbeds (gravelly sands), with saturated hydraulic conductivities up to the order of 10 -1 cm/min. Such deposits often cover steep slopes, which stability is guaranteed by the apparent cohesion due to suction under unsaturated conditions, that are the most common conditions for these slopes [Olivares and Picarelli, 2003]. Whereas rainfall infiltration causes soil to approach saturation, suction vanishes and slope failure may occur. Besides soil physical properties, landslide triggering is influenced by several factors, such as rainfall intensity, soil initial moisture and suction, slope inclination, boundary conditions. Whereas slope failure occurs with soil close to being saturated, landslide may develop in form of fast and destructive flowslide. Calibration of reliable mathematical models of such a complex phenomenon requires availability of experimental observations of the major variables of interest, such as soil 1461