The weathering product clays of the graphitic shales and their effects on the sliding case study: Narlıdere landslide area - İzmir

Bornova Melange (flysch) composed of sandstone-shale intercalations is commonly outcrops in the Izmir area. Shales are rather widespread in Balçova and Narlıdere, south of the Izmir Bay. Presence of the three different lithological levels in the soil profiles obtained from the borehole data, 1/1000 scaled engineering geological maps and geological cross-sections has been drawn attention; 1. Artificial fills (stripping materials) 2. Autochthonous rocks belonging to the Bornova Melange which is composed of sandstone and shale intercalations. 3. Grey colored, highly and/or completely weathered bitumnious shales with carbon content (<7%). The shales in the melange are placed in as lences. Potential landslide areas appeared due to the high angle slopes of Izmir fault and also extreme rains affected these areas. In this study, engineering geology, geotechnical investigations and slope stability analysis, petrographical and XRD analysis carried out to determine engineering properties of the materials in Narbel (Narlıdere) and Kabaoğlu (Balçova) landslide areas. Determination of sliding mechanisms of the landslides, the positions of possible sliding surfaces and soil types and slope stability problems which may occur at today and/or under the dynamic conditions are tried in this study. Borings with cores were drilled in the field and boring locations were determined with the help of field works. Attenberg limits, uniaxial compressive strength, point load and direct shear tests were conducted to determine geotechnical parameters of the samples taken from drillings. Laboratory tests were conducted in soil-rock mechanics laboratory of the Dokuz Eylul University, Geological Engineering Department. ix Standard Penetration Tests (SPT) were performed in soil levels of the soil profiles during the drillings and gathered data used to determine the locations of the sliding circles in the landslide areas. Also, SPT-values were used to calculate bearing capacity of soils and draw the soil profile in the plain areas with flat topography. Plaxis software was used in slope stability analysis in the landslides. The method of nonlinear definite elements was used during these analysis. Slope stability analysis conducted using the Plaxis Software were directly taken from DEVAK (2005a). ın this study, the results of slope stability analyses were evaluated with respect of the engineering geology. Depth of the sliding circles of the landslides are 32 m. and 23 m. in the T80 location and Hasan Icyer Primery School garden area respectively. Bitumnious shales in the locations above mentioned are under the water saturation conditions. Bitümnious shales (percantage of carbon content < 7%) in these locations are graded as weak rock to hard soil with respect to their strength. It is determined that the shales in under the water saturation conditions are weathered to the soil material when they are affected in the weathering process, have been controlled to the slides. They store water from precipitations and the areas become continiously wet by the seepages occurring from the fills. By the time, the water content of completely weathered bituminous shales increase and there will be a considerable reduction in shear strength parameters of this material. As a result, the lower parts of the slopes become landslide prone areas loaded also by stripping material. During the field studies, it was observed that wide areas were affected by slope movements which resulted in artificial loading and saturation of the slopes by seepage water in along time. In this study, two mass movements occurred at the slopes which are loaded by stripping materials overburden removal of the Narbel housing and Kabaoğlu landslides areas have been evaluated. Key words: Narbel (Narlıdere-Izmir), Kabaoğlu (Balçova-İzmir), landslide, graphitic shale.