Investigation of the engineering properties of quaternary sediments at Afsin-Elbistan basin Collolar region

Afşin Elbistan basin, which is located in the Southeastern of Turkey, has an area of approximately 900 km2 and an average altitude of 1200 m above mean sea level. At the base, karstic limestones form the main rock. The karstic limestones are covered by a clay layer with a thickness about 100 m. A series of lignite deposits, which have the thickness of 20-50 m, overlie the clay layer. Above lignite layer, gytja was deposited. This entire sequence is covered by the Quaternary sediments. The lignite series, which are highly profitable, had been excavated in the Kışlaköy and Çöllolar Region by using open pit mining method at the basin formed in the lake environment. Two landslides, of which the first one occured on the southwestern slope on February 6, 2011, and the second one occured on the northeastern slope on February 10, 2011 in Çöllolar open pit mining. The second and the largest landslide of them resulted from the failure of the northeastern slope and the landslide material covered an area about 2 km2. In the first landslide 1 person and in the second landslide 10 people lost their lives. In previous studies, there was not a common opinion about the reasons of mass movements and what parameters triggered these movements in the Kahramanmaraş Province, the Afşin-Elbistan District, the Çöllolar Region. It is desired to clarify this issue by the work to be done in the region. Totally 6 boreholes were opened at different locations to determine the engineering properties of the Quaternary sediments at the Çöllolar Region. 64 undisturbed (UD) samples which are 10 cm in diameter and 75 cm in length were taken from the drilled holes. The UD samples were scanned in full section by the tomography device. After the scanning process, the physical conditions of the samples in the tubes were examined to observe whether samples were damaged or not. The samples suitable for the experimental study were separated from other samples. 5 UD samples selected from these samples were used in this thesis study. The selected samples were removed from the tubes by a mechanical tool ,and natural water content test was conducted in order to determine the in-situ water content of the samples. Results obtained from this experiment are important in terms of contribution for further experiments. As a result of the experiment, the natural water content of the samples varies between 28% and 33%. According to the results of analyses, it was observed that UD-59 samples had homogeneous distribution, yet the UD-28, UD-44, UD-46, UD-60 samples had heterogeneous distribution, and characterized by fine-grained delta sediments and lake environment. The wet and dry sieve analyses and hydrometer analysis were used to determine grain size distribution. The grains having size from 8 mm to 0,063 mm were tested by using wet and dry sieve analysis, and the other grains having size less than 0,063 mm were tested by using hydrometer analysis. According to the Atterberg limits, liquid limit values were found between 39% and 86%. The plastic limit results were measured between 29% and 36%. With the results obtained from these two experiments, the plasticity index was measured between 11% and 50% values. The groups in which the soil sample was included were found by putting those samples into the Cassagrande plasticity chart modified by Raman (1973). By using the data of grain size distributions and Atterberg limits obtained from various experiments, soil class of the samples was determined according to the USCS (Unified Soil Classification System). UD-28 sample taken from the 35,90-36,65 m range from the HY-3 borehole was determined as CH (fat clay). UD-44 sample taken from the 28,47-28,47 m range and UD-46 sample taken from the 29,22-29,97 m range from the HY-4 borehole were resulted in ML (sandy silt), respectively. UD-59 sample taken from the depth of 28,25-29,00 m range and UD-60 sample taken from the depth of 3,50-34,25 m range from HY-5 borehole were defined as CH (fat clay). Plasticity index-clay percentage graph of samples from Atterberg consistency limits was prepared, and activity graph was prepared with help of Van der Merwe (1964) activity subdivision. According to the graph, UD-44 and UD-46 have low activity, UD-28 has moderate activity, UD-59 has high activity and UD-60 very high activity. By comparing the degrees of sensitivity and activity values, soil samples with low activity have been found to have low sensitivity whereas soil samples with relatively very high activity have been found to have less sensitivity. The Enslin-Neff test was conducted to measure the water uptake capacity of soil samples. The amount of water that 1 g test sample can be taken was measured. In the experiment, the first increasing water content value indicates the capillarity, where the the top value refers to the degree of swelling of the soil. According to Enslin-Neff test results, the water uptake capacity varies between 58% and 83%. As a result of the oedometer test, the initial wet densities of the samples were 1,7-1,9 g/cm3, where final wet densities were 2,0 g/cm3. The initial dry densities were 1,2-1,5 g/cm3, where final dry densities were determined as 1,4-1,6 g/cm3. One of the tests which is applied to determine the shear strength of the soil is vane test. It enables to calculate the degrees of sensitivity of soils directly. The undisturbed samples were not able to be used for vane test. Hence, laboratory vane experiment was carried out with only reshaped samples obtained from undisturbed samples. Therefore, the only value obtained from vane test is shear strength of soil samples. They had densities ranging between 1,7-1,8 g/cm3. When these densities are found, the densities obtained from the oedometer experiments are taken into account. Shear strength was determined from the vane test by using spring-1 abutment. The shear strength values corresponding to the angle on abutment face were determined. According to the laboratory vane test results, average value is 15 kN/m2 for remoulded shear strength of UD-28, average value is 15 kN/m2 for UD-44, average value is 10 kN/m2 for UD-46, average value is 25 kN/m2 for UD-59 and average value is 22 kN/m2 for UD-60 sample. Direct shear test was applied in order to determine the shear parameters. For the calculation of degree of sensitivity of UD-44 and UD-60 samples, firstly the shear parameters of undisturbed samples were calculated and then the shear parameters of remoulded samples were determined. The ratio between the shear strength of undisturbed and remoulded samples refers to the degree of sensitivity. According to the direct shear test calculations, applied on sample 44 and 60, the peak values of internal shear angles vary between 12 and 26 degrees, and the residual values are ranged from 6 to 13 degrees. The cohesion values were found between 32-139 kN/m2. Based on experiments carried out, sensitivity for sample UD-44 were found as 1,2 for 200 kN, 1,5 for 400 kN and 1,7 for 800 kN. The sensitivity were determined as 1,9 for 200 kN, 1,9 for 400 kN and 1,4 for 800 kN for sample UD-60. These values fall into the class of less sensitive soil according to Skempton and Northey (1952) the classification of the sensitivity of soil. Engineering properties of soil such as internal friction angle, cohesion and index properties of soils show harmony between the Çöllolar field and the Norwegian sediments. UD-44 and UD-60 were chosen between 5 UD samples. Since these two samples were completely different from each other according to the grain size analysis and atterberg limit. According to the direct shear test, the 200 kN load did not cause any changes in the seating of material. The UD-60 clay sample had previously been subjected to a load more than 200 kN and the 200 kN load showed no effect on the vertical behaviour of the material. On the other hand, 400 kN had caused a change in vertical position. Sensitive clay deposits mostly consist of clays seen in the glacial environment as in Canada and Norway. However, Afşin-Elbistan basin is one of the distinctive basins in the world which includes sensitive clay even it was not formed in the glacial environment.