Geology of the Gönen region (Balıkesir) and the effect of ground water on slope stability in the region

This study is carried out to investigate the geotechnical movements and the geological characteristics of the region in the landslide of the Gönen-Yenice road km: 13+000 Kumköy location in the Gönen District of Balıkesir City. Late Oligocene-early Miocene Hallaçlar volcanite is the first unit stratigraphically located at the bottom of the study area and widely observed in the region and unconformably overlies the basement rocks. The Pliocene-aged Bayramiç Formation and the Quaternary-aged Alluvium unconformably cover all the rock units in the region. In this study, it was determined that the landslides in the region were formed on the Pliocene aged Bayramiç formation and the Quaternary aged Alluvium units. Within the scope of studies on landslide formation triaxial compression tests (UU), the cohesion (c) value for sample UD-1 obtained from borehole SK-2 was determined to be sturdy at 46 kPa, and the internal friction angle was determined to be loose (φ) at 12° and for sample UD-1 obtained from borehole SK-3, the cohesion value was determined to be sturdy at 65 kPa, and the internal friction angle was determined to be loose at 7°. According to the direct shear tests (CD), for sample UD-1 obtained from borehole SK-1, the peak cohesion value was determined to be soft at 36 kPa, and the internal friction angle was determined to be loose at 38°, the residual cohesion value was determined to be soft at 32 kPa, and the residual friction angle was determined to be loose at 33°; for sample UD-2 obtained from borehole SK-3, the peak cohesion value was determined to be soft at 10 kPa, and the internal friction angle was determined to be very loose at 21°, the residual cohesion value was determined to be soft at 8 kPa, and the residual friction angle was determined to be very loose at 19°, and for sample UD-1 obtained from borehole SK-2, the peak cohesion value was determined to be soft at 22 kPa, and the internal friction angle was determined to be 35°. Based on the point load tests conducted on samples taken from the rock specimens, for the sample obtained from the unit referred to as claystone-1, the cohesion value was determined to be very weak rock at 36 kPa, and the internal friction angle was determined to be moderate rock at 28°; for the sample obtained from the unit referred to as claystone-2, the cohesion value was determined to be very weak rock at 70 kPa, and the internal friction angle was determined to be moderate rock at 26°; for the sample obtained from the unit referred to as intercalation-1, the cohesion value was determined to be very weak rock at 72 kPa, and the internal friction angle was determined to be good rock at 37.5°; for the sample taken from the unit referred to as intercalation-2, the cohesion value was determined to be very weak rock at 92 kPa, and the internal friction angle was determined to be good rock at 37.5°, and for the sample taken from the unit referred to as intercalation-3, the cohesion value was determined to be weak rock at 118 kPa, and the internal friction angle was determined to be good rock at 37.5°. It has been determined that the soil movements detected in the study area take place within the silt units observed up to a depth of approximately 10 m, these movements still continue, albeit slightly, in some areas, and the changes in precipitation and groundwater levels affect the safety coefficient for the region.