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Geotechnical characterization of soils prone to rainfall-induced landslides in Rize (Northern Turkey)

Üyetürk, Celal Emre
Landslides are common type of natural hazards around the world. Every year, hundreds of landslides are induced by rainfall in Rize. These landslides are shallow failures, generally having a maximum depth of 5 m. Although many of these landslides are observed every year, there is limited data on characteristics of these soils in the literature. Characterizing these soils is of paramount importance for numerical modeling of the landslide mechanisms, for landslide susceptibility mapping and for establishing rainfall intensity-duration thresholds. This study aims to investigate the characteristics of soils in rainfall-induced landslides in Rize. Disturbed and undisturbed samples are taken from a total of 12 landslide sites to evaluate the physical and mechanical properties and the mineralogy. Experiments including grain size distribution, Atterberg limits, organic content by mass and pH determination, mineralogy studies via X-Ray diffraction and Scanning Electron Microscopy, direct shear tests, unconfined compression tests, soil-water retention studies, hydraulic conductivity tests are conducted. Also, in-situ unit weights are determined on undisturbed samples, and portable hand vane tests are conducted to evaluate the in-situ undrained shear strength. Results indicate that these materials are relatively loose, medium-stiff, mostly fine-grained soils (low and high plasticity silts and high plasticity organic soils), and have relatively low pH. Direct shear tests on intact samples indicated that the average internal friction angle is in the range of 31.1-38.0 degrees in saturated condition; on reconstituted samples revealed the degree of saturation effects the shear strength and the volumetric response significantly.