Buyukcekmece-Gurpinar residential area relation between soil classification and slope stability

The purpose of this thesis study is to present recommendations for the design of slope regulations suitable for the probably urbanization that is to be done in this area in the future, which has remained relatively untouched and which sits on the edge of a lake on the European side of Istanbul, by identifying the relationship between the ground classification and slope stability in the settlement area with the E-80 Europe Motorway in the north, the Marmara Sea in the south, the border of Büyükçekmece Lake and Büyükçekmece Cove in the west, and the Europe Motorway- Hadımköy Connection in the east, that later extends from the length of the Yavuz Sultan Selim Boulevard and Ziya Gökalp Avenue line to the Marmara Coast. Bureau, field survey, and laboratory studies were conducted, respectively, for the purpose of obtaining the targeted outputs; and findings and opinions were revealed by compiling the acquired data. General geological findings were provided based on the field survey and literature studies conducted in the field of investigation. It was determined that sedimentary deposits from the Oligocene and Miocene epochs surfaced; that - from old to young - the Gürpınar formation, the Çukurçeşme formation, the Güngören formation, and the Bakırköy formation created stratigraphic distribution; and that the Miocene deposits came with angular unconformity over the Oligocene deposits. It was observed that while the layer slopes generally have a horizontal or very low slope, they increased at the points at which mass movements were seen. Samples were taken from 16 points in the field survey, and sieve analysis and Atterberg consistency limits tests were conducted in the ITU - Geological Engineering Department Index Properties Laboratory for the identification of the soil classification along with physical feature tests (pycnometer, porosity, and water content), which were conducted to identify the engineering and design parameters. The results obtained from the laboratory tests were combined, and soil identifications were made using the soil classification - USCS system. When the soil identifications for the 16 samples were examined, it was seen that the examination area was formed from mostly coarse sand and that graveled levels were common. Fine-grained units of soil, however, presented a spread in a limited area in the northern section throughout the Büyükçekmece coast. Within the scope of the thesis study, the relationships between soil classification and slope stability were identified with the acquired data in the research area, which has been relatively untouched, which is on the edge of a lake, and in which it is known with previously conducted research that it is a risky region in terms of slope stability and mass movements on the European side of Istanbul. For the fine-grain soils, preliminary designs were presented for the slope regulations suitable for the probably urbanization to be done in future processes, and what the points are at which precautionary measures need to be taken should tension cracks in the slopes to be regulated form or should groundwater rise were presented. For the coarse-grain soils, however, the equations that will provide the necessary depth for groundwater were revealed so that the safety number required under the designed conditions may be provided, and the relationships that these equations presented based on the soil properties were later examined. Slope stability calculations were made using the c=0 method for coarse-grain soils and the empirical method for fine-grain soils. In the calculations for the fine-grain samples, the limit equilibrium analysis method was used by taking Gs=1, and the slope stability analyses were conducted with the infinite slope approach. The slope stability analyses were calculated based on the slow and fast loading scenario criteria with situations where the soil is completely dry and completely saturated, from the surface of the topography until a depth of 10 m. Seismic load is also taken into consideration for the final slope dimensioning in the calculations made in the fine-coarse soils. In the TS 8853/1991 standard, the safety number was specified as Gs=1.5 for the slope and fissured clays in the slope. Because the proximity of the research area to the North Anatolian Fault line is found within the 1st and 2nd degree seismic belt, it was specified as Gs=1.6 in the stage of the seismic analysis, and the slope analysis was completed. For situations of the rise of groundwater, which is a factor that will cause slope instability with time in the slopes for which preliminary designs are presented for the fine-grain soils, and of the formation of tension cracks in the immobile section of the slope; the slope stability was inspected with the reverse analysis method, and the critical static water levels (Hsu) and the lengths (L) and densities (D) of the mass that will offset the slope in relation to the tension crack. Only the index-physical properties for the samples were used in the calculations of these preliminary designs that were made for the probable slopes to be made in this area in which fine-grain soils dispersed. It was first specified that the most suitable slope rate was 1.5:1 (horizontal-vertical, α=33.69°) for all slopes in the calculations made, without considering the seismic load. Seismic load was later added into these accounts, and the calculations were continued in this direction. Because it is known that the terrain is within the 1st and 2nd degree seismic zones near the North Anatolian Fault line and that it is a risky region in terms of mass movement, an attempt was made to remain on the safe side throughout all the calculations and the safety number (Gs) of 1.6 and a seismic coefficient (ky) of 0.25 were chosen. Thus, the objective is for the slope structures for which we have provided preliminary designs to survive a possible Istanbul earthquake with the least amount of damage. Should the groundwater be in the ground or on the surface, the serious differences between the vertical distances that were offered for the slopes, without considering seismic load, demonstrate how much drainage measures need to be paid attention to for the structure for any kind of urbanization. Should the groundwater level be decreased in a water-saturated slope for the fine-grain soil sections of the Gürpınar formation of the relationships between the critical slope heights that were specified for Gs=1, an equation has been suggested regarding what the slope height in the dry environment needs to be. While the initial slope angle was 10° in the calculations made for the coarse soil, analysis was maintained for the analysis Gs=1 starting from the condition of the groundwater being 10 m. (YAS=10 m.) beneath the surface of the topography until the condition of its rising by approaching the surface of the topography of the groundwater level, throughout a possible sliding plane at a depth of 1 m., 2 m., and 3 m. from the surface of the topography. The analysis results identified what the groundwater level (YAS) will be for the situations in which the safety number (Gs) varies between 1-3 for a slope angle of 10° at each sample point for the course-grain soils, and general equations were recommended for course-grain levels of the Gürpınar formation. The Slope Angle-YAS relationship was examined in the slopes in which the slope angle varied between 20°-30° in the progressing section of the conducted analysis, and while Gs=1, general equations were recommended for the situations in which the sliding plane varied between 1-3 m. The relationships that the samples showed were later examined in both conditions. The Gs-YAS and Slope Angle-YAS relationships that the coarse-grain soil samples presented under the designed conditions were revealed with the equations. The obtained equations were generalized based on the soil classification, on there being sand or gravel, and lastly on there being coarse-grain soil all together, by making groupings and by using the geometric mean method. The equations generalized based on soil classification presented relationships close to each other. After the equations for each coarse-grain soil sample were grouped based on the soil classification, whether there was sand or gravel, and lastly on there being coarse-grain soil all together; a few low differences were seen on average when compared with the suggested equations. Equations were put forth that would be able to calculate the depth at which the groundwater level needed to be in a fast and reliable manner, if it is only known that the soil is coarse-grain, in order to be able to provide the safety number (Gs) values between 1-3 with the equations presented in the Gs-YAS condition and to provide the values between 10-30° for the slope angle with the equations presented in the Slope Angle-YAS condition. All of these evaluations that were conducted were based on field survey observations, information obtained from the literature, and calculations made with test results. This study put forward recommendations for slope designs for urbanization by using index and physical features, identified critical points for agents that may lead to slope instability, and researched the relationship between these with soil classes. While it is known that the investigation area is a region that poses a risk in terms of mass movements, it is highly probably that its structuring will proceed in this direction and that with time, many structures will be constructed here. The scope of this study is in the presentation of suggestions of preliminary designs for slopes with the use of the points currently taken as examples and the data acquired from the decided laboratory tests, in the identification of the relationship between soil class-slope stability, with the help of the information in the literature. With the results of the tests conducted in laboratory conditions, it is obvious that the possibility that there may be differences between the natural conditions on the terrain will be unable to be evaluated with only 16 samples with all of a 56 km2 area, when considering that geological features can vary even in short distances. It is necessary to conduct more detailed geological and geotechnical studies in the construction of comprehensive engineering structures. The equations and values that were revealed within the scope of this thesis may be used as a preliminary etude approach while conducting studies relating to the soil class that we described in the Gürpınar formation in the investigation area. It will be necessary to identify the sliding resistance values (internal friction angle and cohesion) for the undisturbed samples to be taken from the area over which an investigation is being considered. Considering the potential of an Istanbul earthquake in the future, settlement suitability evaluations that are supported with detailed geological and geotechnical research should be conducted in the untouched terrain to the east of Büyükçekmece Lake, which sits especially between the D-100 highway and the E-80 Europe Motorway; and geological soil etude reports need to be carried out based on the detailed zoning prior to the construction of the engineering structures.