Geotechnical investigation of landslides occurred on the highways in the Siirt region

Landslides cause serious economic losses and create security risks, especially on highways constructed on sloping terrains. This thesis is intended to study the landslides along the highways in the Siirt region (eastern Turkey) from a geotechnical point of view and to effectively analyse the problems caused by them. Within the scope of the study, the landslide that occurred during the highway construction on the route between Km: 13+600 – 14+600 in Aktaş village of Kurtalan district of Siirt province was discussed. High cut and fill sections were encountered in the study area, therefore this section is evaluated as having critical importance. Characteristic features of the landslide area were determined through field observations, drilling data, geotechnical studies and slope analysis. Effects of topography, ground properties, groundwater level, net supply rainfall as well as the engineering design on the occurrence of the landslide were taken into consideration during the study. In the mentioned route, an extensive experimental study was carried out on the clayey silty unit and gypsum levels of the Germik formation under saturated and unsaturated soil conditions. The experimental data obtained is evaluated to be significant in terms of validating the analyses made prior. Direct shear tests were carried out at 49% and 100% saturation degrees, and the stability analysis configuration was determined with the residual effect obtained and the saturation degree-safety structural connection. Subsequently, slope stability analyses of the ground under the influence of rainfall infiltration were carried out. In the analyses the effects of changes in various values of water absorption, different groundwater levels and rainfall amounts on slope stability were examined. Numerical analyses were made to determine the collapse surfaces on the model reflecting the current situation using the softwares Plaxis 2D V24, which is based on the finite element method, and Slide-2, which is based on the limit equilibrium method, and therefore calculations for safety factor analysis in relation to collapse surfaces were made.