Rainfall thresholds for landslide early warning system in Nakhon Si Thammarat
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ORIGINAL PAPER
Rainfall thresholds for landslide early warning system in Nakhon Si Thammarat Chollada Kanjanakul 1 & Tanan Chub-uppakarn 1 & Tanit Chalermyanont 1
Received: 26 April 2016 / Accepted: 25 July 2016 # Saudi Society for Geosciences 2016
Abstract Transient seepage in unsaturated soil slope is one of the significant triggering factors in rainfallinduced landslides. Rainfall infiltration leads to the decrease in stabilizing effect because of increased positive pore-water pressures. SEEP/W and SLOPE/W used in this study have been widely employed to describe frameworks for understanding transient seepage in soil slope, and to perform slope stability analyses, respectively. The study area is in Sichon District in Nakhon Si Thammarat Province, southern Thailand. A landslide there was investigated by modeling the process of rainfall infiltration under positive and negative pore-water pressures and their effects on slope stability. GIS (Geographic Information System) and geotechnical laboratory results were used as input parameters. The van Genuchten’s soil water characteristic curve and unsaturated permeability function were used to estimate surface infiltration rates. An average rainfall was derived from 30-year monthly rainfall data between 1981 and 2011 in this area reported by the Thailand Royal Irrigation Department. For transient condition, finite element analysis in SEEP/W was employed to model fluctuations in pore-water pressure during a rainfall, using the computed water infiltration rates as surface boundary conditions. SLOPE/W employing Bishop simplified method was then carried out to compute their factors of safety, and antecedent precipitation indices (API) calculated. Heterogeneous slope at the site became unstable at an average critical API (APIcr) of 380 mm, agreeing well with the actual value of 388 mm. * Chollada Kanjanakul [email protected]
1
Prince of Songkla University, Hat Yai, Songkhla, Thailand
Keywords Antecedent precipitation index (API) . Landslides . Slope stability analysis . Unsaturated soil
Introduction Landslide poses a natural hazard and disaster. Many factors contribute to landslide probability such as erosional history, geology, tectonic history, slope gradients, drainage network, and land-use (Casagli et al. 2006; Bathrellos et al. 2012). Engineers have constantly tried to find better methods of warning systems to mitigate the problem. Rozos et al. (2011), for example, compared rock engineering system and an analytic hierarchy process that were adopted in a GIS environment for compilation of corresponding landslide susceptibility maps; these maps were reported to have given useful information of the causal parameters and the landslide manifestation in the Eastern Achaia County of Peloponnesus, while Lee et al. (2016) used GIS database, landslide-related items to calculate probability of landslide in Inje, Korea— assuming that the landslide was triggered by a very high daily rainfall or a 3-day cumulative rainfall—and predicted that heavy rainfalls were expected t
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