A geotechnical study on the landslides in the Trabzon Province, NE, Turkey

In the Trabzon province at the Eastern Black Sea region in Turkey, there are small and large landslides, especially following heavy rainfall periods in every year. These landslides regularly result in the loss of lives and properties. In this study, an assessment on the geotechnical characteristics of the areas where the landslides occur and the immediate vicinity were compared with the characteristics of non-landslides areas. A total of 50 landslides occurring in different locations were studied. As a result of the geotechnical investigations, the average of liquid limit values were between 49% and 69%, and the average plasticity index of the units ranged from 9% to 19% in the overlying materials in the landslide areas. Heavy rainfall exceeding boundary saturation of soils plays a critical role in causing landslides. According to the Unified Soil Classification System, the soils were “silts of high plasticity and silts, silty or clayey fine sands of low plasticity”. 80% of the total landslides occurred within very high and completely weathered units of basalt, andesite, or pyroclastics, and intercalations of sandstone, clayey limestone and siltstone. This study shows that the shear strength parameters decreased with increasing moisture content and that the number of landslides increased in relation to the particle size distribution of the clay.