Assessment of landslide susceptibility for a landslide-prone area (north of Yenice, NW Turkey) by fuzzy approach

. Regional landslide susceptibility assessments pose complex problems. To solve these problems, numerous approaches, such as statistical analysis, geotechnical engineering approach, geomorphologic approach and fuzzy logic, have been employed. However, all the available methods for regional landslide susceptibility assessments have some uncertainties due to a lack of knowledge and variability. Minimizing these uncertainties provides realistic approaches. Use of the fuzzy logic approach to produce a landslide susceptibility map of a landslide-prone area in NW Turkey is the main purpose of the present study. For this purpose, the study includes five main stages, these being the preparation of a landslide inventory of the study area, the application of factor analysis, the extraction of fuzzy if-then rules, the use of a geographical information system, and the control of the reliability of the resulting landslide susceptibility map. Slope angle, slope aspect, land use, weathering depth, water conditions and topographical elevation were considered as landslide conditioning factors for the study area. A total of 23 if-then rules was extracted from the field data. Employing these rules, fuzzified index maps representing each parameter were obtained. Finally, combining these maps, the landslide susceptibility map of the area was prepared. When compared with the landslide susceptibility map, the landslides identified in the area were found to be located in the very high- and high-susceptibility zones. As far as the performance of the fuzzy approach for processing is concerned, the images appear to be quite satisfactory, the zones determined on the map being zones of relative susceptibility.     

Application of logistic regression and fuzzy operators to landslide susceptibility assessment in Azdavay (Kastamonu,Turkey)

Landslides and their assessments are of great importance since they damage properties, infrastructures, environment, lives and so on. Particularly, landslide inventory, susceptibility, and hazard or risk mapping have become important issues in the last few decades. Such maps provide useful information and can be produced by qualitative or quantitative methods. The work presented in this paper aimed to assess landslide susceptibility in a selected area, covering 570.625 km² in the Western Black Sea region of Turkey, by two quantitative methods. For this purpose, in the first stage, a detailed landslide inventory map was prepared by extensive field studies. A total of 96 landslides were mapped during these studies. To perform landslide susceptibility analyses, six input parameters such as topographical elevation, lithology, land use, slope, aspect and distance to streams were considered. Two quantitative methods, logistic regression and fuzzy approach, were used to assess landslide susceptibility in the selected area. For the fuzzy approach, the fuzzy and, or, algebraic product, algebraic sum and gamma operators were considered. At the final stage, 18 landslide susceptibility maps were produced by the logistic regression and fuzzy operators in a GIS (Geographic Information System) environment. Two performance indicators such as ROC (relative operating characteristics) and cosine amplitude method (r _ij ) were used to validate the final susceptibility maps. Based on the analyses, the landslide susceptibility map produced by the fuzzy gamma operator with a level of 0.975 showed the best performance. In addition, the maps produced by the logistic regression, fuzzy algebraic product and the higher levels of gamma operators showed more satisfactory results, while the fuzzy and, or, algebraic sum maps were not sufficient to provide reliable outputs.     

Assessment of excavatability,abrasivity and slope stability in a sandstone quarry in Istanbul,Turkey

The Cebeci region is characterized by outcrops of Carboniferous sandstone, including diabase dykes. This region is very important area for aggregate production in Istanbul, Turkey. The aim of this study is to determine the engineering geological properties of sandstones to assess the excavatability, abrasivity and stability of cut slopes in a quarry site. Firstly, the sandstone samples were used to determine their petrographical and mineralogical characteristics. Then, physico-mechanical tests were performed on these samples. In order to determine rock mass properties, scan-line surveys were performed, and the major orientations of discontinuities were analyzed through the stereographic projection technique. Kinematical analyses were also made to determine the potential failures at the quarry site. According to the results obtained, excavatability is changed from easy ripping to hard ripping on sandstones; the carbonated sandstone is less abrasive than other sandstones. Based on the field studies and stability analyses of the cut slopes, optimum slope geometry and necessary support measures, such as wire mesh and rock fall barriers, are suggested.     

九台地区岩质边坡稳定性及运动过程评价方法探讨

文章对九台地区岩质边坡的稳定性及运动过程进行了评价方法的探讨,通过岩质边坡的发育特征,分析了边坡失稳的原因,通过赤平投影图与离散元数值模拟对边坡的稳定性进行了分析,并对边坡崩塌的范围进行了预测,为边坡的稳定性计算提供借鉴参考.     

Soil liquefaction susceptibility and hazard mapping in the residential area of Kütahya (Turkey)

This study presents the results of both field and laboratory tests that have been undertaken to assess liquefaction susceptibilities of the soils in Kütahya city, located in the well-known seismically active fault zone. Liquefaction potentials of the sub-surface materials at Kütahya city were estimated by using the geological aspect and geotechnical methods such as SPT method of field testing. And, the data obtained have been mapped according to susceptibility and hazard. The susceptibility map indicated “liquefable” and “marginally liquefable” areas in alluvium, and “non-liquefable” areas in Neogene unit for the magnitude of earthquake of M=6.5; whereas, liquefaction hazard map produced by using of liquefaction potential index showed the severity categories from “very low” to “high.” However, a large area in the study area is prone to liquefy according to liquefaction susceptibility map; the large parts of the liquefable horizon are mapped as “low” class of severity by the use of the liquefaction potential index. It can be said that hazard mapping of liquefaction for a given site is crucial than producing liquefaction susceptibility map for estimating the severity. Both the susceptibility and hazard maps should be produced and correlated with each other for planning in an engineering point of view.     

The importance of hydrogeological and hydrological investigations in the residential area: a case study in Burdur,Turkey

Water resources in residential areas are negatively affected by floods. In addition, many aquifers are contaminated as a result of urbanization. Great damage caused during earthquakes are partly attributed to the residential pattern which ignores the potential effect of groundwater. Hydrogeological and hydrological surveys must be carried out in the residential areas to determine the interaction between water and residential development of all types.Recent hydrogeological and hydrological investigations regarding the impact of urbanization were made for the city of Burdur (Turkey). To evaluate the effect of earthquakes on groundwater, groundwater isohypse and groundwater isopach maps were prepared showing most of the buildings within the Burdur city boundaries, which are in the areas where groundwater depth is less than 10 m. This is considered a critical depth for liquefaction during an earthquake. Lowering of the groundwater table has to be considered as one of the alternatives in reducing earthquake hazards. The chemical makeup of groundwater was also determined to consider its relationship to contamination and possible effects upon the foundations. Streams flowing across the Burdur residential area formed a flooding risk. Results of the peak flow analysis can be used to design improvements for the city. Maps of the best residential development areas have been prepared by using hydrological and hydrogeological results.     

Evaluation of rock excavatability and slope stability along a segment of motorway,Pozanti, Turkey

The Çiftehan-Pozant segment of the Ankara-Pozant motorway is problematic due to the existence of lithological units with variable character. Seven cut slopes are planned along Km 358+000– Km 364+350 of the proposed motorway. The purpose of this study is to determine engineering geological properties of the rocks exposed along the motorway and to assess the excavatability and stability of the cut slopes. Both field and laboratory studies were carried out during this study. Field studies involved geological mapping, detailed discontinuity surveying and sampling. Laboratory tests were carried out to determine unit weight, point load strength index and shear strength parameters of the discontinuities. In the study area, recrystallized limestone, microgabbro, conglomerate and Quaternary deposits are exposed. However, the cut slopes are located within microgabbro and conglomerate. Hard to very hard ripping with local blasting for the fresh inner part of the rocks is recommended for the excavatability. In two cut slopes wedge failure is expected, whereas in another two slopes both wedge and toppling failures are likely to occur. Based on the field observations and stability analyses of the cut slopes, slope flattening with various angles, wire mesh, and drainage ditches are proposed.     

The landslides threatening Tasova town (Central Anatolia, Turkey) and their environmental impacts

There exist a number of landslides along the north Anatolian fault zone (NAFZ) between Tasova and Alparslan in Amasya province in Turkey. These landslides extending over an area of 2.5 × 6.0 km are triggered by steepening of slopes due to undercutting by the Yesilirmak River and groundwater fluctuations. The landslides have affected 30 buildings in the western part of Tasova. In this study, in order to investigate the engineering geological characteristics of the landslides and their environmental impacts, representative samples from geological units were collected and a total of six boreholes were drilled. Plastic pipes were installed into the boreholes to measure the groundwater fluctuations and to determine the position of the sliding surface. For a two-year monitoring period, using a GPS linked to a fixed station system, the magnitude of the movements ranged between 11.7 and 17.6 cm at the toe of landslide. The landslides that occurred in the study area were in the form of retrogressive circular and multiple circular failures. The factor of safety along a number of cross-sections calculated by the limit-equilibrium method of analysis is 0.96 in static condition. After further analyses, construction of a toe buttress with surface drainage may be suggested as a remedial measure to minimize the effects of these landslides.     

The Manyas fault zone (southern Marmara region,NW Turkey): active tectonics and paleoseismology

The Manyas fault zone (MFZ) is a splay fault of the Yenice Gönen Fault, which is located on the southern branch of the North Anatolian Fault System. The MFZ is a 38 km long, WNW–ESE-trending and normal fault zone comprised of three en-echelon segments. On 6 October 1964, an earthquake (Ms = 6.9) occurred on the Salur segment. In this study, paleoseismic trench studies were performed along the Salur segment. Based on these paleoseismic trench studies, at least three earthquakes resulting in a surface rupture within the last 4000 years, including the 1964 earthquake have been identified and dated. The penultimate event can be correlated with the AD 1323 earthquake. There is no archaeological and/or historical record that can be associated with the oldest earthquake dated between BP 3800 ± 600 and BP 2300 ± 200 years. Additionally, the trench study performed to the north of the Salur segment demonstrates paleoliquefaction structures crossing each other. The surface deformation that occurred during the 1964 earthquake is determined primarily to be the consequence of liquefaction. According to the fault plane slip data, the MFZ is a purely normal fault demonstrating a listric geometry with a dip of 64°–74° to the NNE.     

Determination of joint roughness coefficient (JRC) for slope stability analysis: a case study from the Gold Coast area, Australia

Surface roughness of rock discontinuities is an important factor that determines the strength characteristics of rock mass. Joint roughness coefficient (JRC), which is typically measured by means of Barton’s combs in the field, is widely used to describe the joint roughness. However, this traditional method of measurement can be rather subjective, labor-intensive and time consuming. In contrast, photogrammetry can provide an alternative method to obtain relatively simple and fast measurements of JRC based on high resolution 3D models. However, the reliability of such measurements still remains an issue as the results from photogrammetry can be affected by the quality of images. This study seeks to clarify whether photogrammetry can produce accurate measurements of JRC that can be used to assess the stability of slopes. A rock slope with a recent wedge failure in the Gold Coast area, Australia was selected for this purpose, and three different methods such as manual measurements, photogrammetry, and tilt tests were employed to determine the JRC. The obtained results showed some discrepancy in the values of JRC obtained from these three different measurements. In particular, the JRC obtained using the Barton’s comb had slightly higher values compared to those determined through the photogrammetry method while the tilt test results tended to yield overestimated values of JRC. Computer analysis using Universal Distinct Element Code was also performed to study the effect of JRC variation on the slope stability. It was found that an increase in the JRC led to an increase in the safety factor of the slope.     

Using tree-ring signals and numerical model to identify the snow avalanche tracks in Kastamonu,Turkey

Many parts of our planet are exposed to natural disasters such as snow avalanches, floods and earthquakes. Detailed knowledge on these natural disasters is crucial for human safety. On December 25–26, 1992, two avalanches occurred at Kayaarkası-Kastamonu in northern Turkey. The first avalanche took place at night of 25–26 December and caused no damage. The second avalanche took place at morning of 26 December, killed four people and did damage to properties. The purpose of the present study is to determine the effects of the snow avalanches on tree rings and to investigate the boundaries and velocities of the avalanches using a numerical simulation model and the tree-ring data. Increment cores from 71 trees in the avalanche-impacted area and the control site were sampled to obtain individual standard chronologies. In the analyses, trees were grouped as (1) heavily damaged by the avalanche, showing a decrease in tree-ring widths since the event, (2) trees heavily damaged by the avalanche, showing an increase in tree-ring widths a couple of years later the event and (3) trees that were not damaged by the avalanche. In this study, one of the most important results is the precise determination of the temporal and spatial patterns of the undocumented avalanche (the first avalanche) event. Avalanches were numerically simulated using dynamical avalanche simulation software ELBA+. Comparison of the simulation model with tree-ring analysis revealed valuable results about the boundaries of the zone of influence of the avalanches.     

Description of dynamics of the Tuzla Landslide and its implications for further landslides in the northern slope and shelf of the Cinarcik Basin (Marmara Sea, Turkey)

Seismic and multi-beam bathymetric data from the northern shelf and slope of the Cinarcik Basin, which is generated by the North Anatolian Fault Zone (NAFZ) located in the easternmost basin in the Marmara Sea, were re-interpreted to better understand the future sub-marine landslide susceptibility. Seismic data indicate that upper surface of the sub-marine extension of the Paleozoic rocks has an NNE–SSW oriented basin and a ridge type morphology controlled by the secondary faults of the NAFZ. Basins are fulfilled by Plio-Quaternary sediments, which are cut by strike-slip faults on the shelf and slope. The thickness of basin deposits reaches up to 130 m toward the linear northern slope of the Cinarcik Basin. A relatively recent sub-marine landslide, the Tuzla Landslide, cuts the slope of the Cinarcik Basin. The detailed morphological investigation indicates that the Tuzla Landslide is a deep-seated rotational landslide, which was likely triggered by activity of the NAFZ. Morphological analyses also indicate that the thick Plio-Quaternary deposits on the Paleozoic basement slid during the Tuzla Landslide event. This landslide is considered as a key event to understand the dynamics of the potential landslides on the northern shelf and slope of the Cinarcik Basin. Two areas locating on the eastern and the western sides of the Tuzla Landslide are considered as the potential areas for future sliding due to similarities of geological and geomorphological features with the Tuzla Landslide such as similar thick Plio-Quaternary deposits, similar slope morphology, and similar fault activity cutting the sediments. Considering this information, the purposes of the present study are to determine the dynamics of the possible landslide areas and to discuss their effects on the sub-marine morphology. In the light of the interpretations, the amounts of possible displaced material are obtained. Three different landslide scenarios due to possible slide surfaces for future landslides are developed and assessed. The first scenario is sliding of the sediments at the shelf break. The third scenario is a mass movement of almost whole basin deposits on the Paleozoic rocks. The latter one is evaluated as less important because of the volume of the displaced material, and the latter one is accepted as lowest possible event. Among the scenarios, the second scenario is accepted as the most critical and possible because of the amount of the slipped material and existence of faults rupture, which is considered as further sliding surfaces. These landslides will result in important changes in shelf, slope and basin floor in the study area.     

A study on geotechnical characterization and stability of downstream slope of a tailings dam to improve its storage capacity (Turkey)

Tailings, waste products of the ore-dressing processes, are usually stored in a slurry form and pumped into sedimentation pond which is surrounded by natural heights and/or artificial walls. The database of International Commission of Large Dams and United Nations Environment Programme showed that several hundreds of tailings dam have failed since 1910. One of the reasons of these failures is slope instability. Construction of mine tailings dams in Turkey has started to increase, particularly in the recent decade. This paper focuses the study undertaken to assess the geotechnical characteristics and stability of downstream slope of a tailings dam at a copper-zinc mine in the Black Sea Region of Turkey. At the mine site there are two tailings dams located at two different elevations. The upper dam was completely filled and is out of service. Increasing amount of tailings filling the pond of the lower dam resulted in a limited storage, and therefore, it has been decided that heightening of the dam about 7 m to improve its storage facility would be necessary. For the purpose, a series of investigations in the vicinity of the tailings dam and some geomechanical laboratory tests were carried in conjunction with the use of empirical methods to determine mechanical properties of the current dam material, tailings and the rockfill material that will be used for heightening of the dam. The results of the static and pseudo-static stability analyses based on the methods of limit equilibrium and numerical modelling indicated that circular and non-circular failures are the most critical modes of failure for the dam and safety factor gradually decreases when the tailings rise up to a specific elevation in the pond. However, the ranges of the calculated safety factors from both methods are considerably similar and suitable for heightening of the dam by 7 m in terms of stability. The results suggest that any instability is not expected under both static and dynamic conditions after the current height of the tailings dam is increased by 7 m, if the slope geometry considered in the analyses is not changed and the tailings in the pond do not rise up to an elevation of about 475 m. In addition, magnitude of permanent settlement of the dam due to a probable earthquake was also assessed using two empirical methods and the results from both methods showed similar amount of settlements which were in tolerable limits.     

A new approach to use AHP in landslide susceptibility mapping: a case study at Yenice (Karabuk, NW Turkey)

This study aimed to investigate the parameter effects in preparing landslide susceptibility maps with a data-driven approach and to adapt this approach to analytical hierarchy process (AHP). For this purpose, at the first stage, landslide inventory of an area located in the Western Black Sea region of Turkey covering approximately 567?km² was prepared, and a total of 101 landslides were mapped. In order to assess the landslide susceptibility, a total of 13 parameters were considered as the input parameters: slope, aspect, plan curvature, topographical elevation, vegetation cover index, land use, distance to drainage, distance to roads, distance to structural elements, distance to ridges, stream power index, sediment transport capacity index, and wetness index. AHP was selected as the major assessment methodology since the adapted approach and AHP work in data pairs. Adapted to AHP, a similarity relation?Cbased approach, namely landslide relation indicator (LRI) for parameter selection method, was also proposed. AHP and parametric effect analyses were performed by the proposed approach, and seven landslide susceptibility maps were produced. Among these maps, the best performance was gathered from the landslide susceptibility map produced by 9 parameter combinations using area under curve (AUC) approach. For this map, the AUC value was calculated as 0.797, while the others ranged between 0.686 and 0.771. According to this map, 38.3?% of the study area was classified as having very low, 8.5?% as low, 15.0?% as moderate, 20.3?% as high, and 17.9?% as very high landslide susceptibility, respectively. Based on the overall assessments, the proposed approach in this study was concluded as objective and applicable and yielded reasonable results.     

Prediction of earthquake hazard by hidden Markov model (around Bilecik,NW Turkey)

Earthquakes are one of the most important natural hazards to be evaluated carefully in engineering projects, due to the severely damaging effects on human-life and human-made structures. The hazard of an earthquake is defined by several approaches and consequently earthquake parameters such as peak ground acceleration occurring on the focused area can be determined. In an earthquake prone area, the identification of the seismicity patterns is an important task to assess the seismic activities and evaluate the risk of damage and loss along with an earthquake occurrence. As a powerful and flexible framework to characterize the temporal seismicity changes and reveal unexpected patterns, Poisson hidden Markov model provides a better understanding of the nature of earthquakes. In this paper, Poisson hidden Markov model is used to predict the earthquake hazard in Bilecik (NW Turkey) as a result of its important geographic location. Bilecik is in close proximity to the North Anatolian Fault Zone and situated between Ankara and Istanbul, the two biggest cites of Turkey. Consequently, there are major highways, railroads and many engineering structures are being constructed in this area. The annual frequencies of earthquakes occurred within a radius of 100 km area centered on Bilecik, from January 1900 to December 2012, with magnitudes (M) at least 4.0 are modeled by using Poisson-HMM. The hazards for the next 35 years from 2013 to 2047 around the area are obtained from the model by forecasting the annual frequencies of M ≥ 4 earthquakes.     

基于强度折减概念的滑坡稳定性三维分析方法(Ⅱ):加固安全系数计算

结合乌江洪家渡1#塌滑体加固设计工程,探讨了滑动面已知的条件下滑坡稳定性的三维分析方法。首先,模拟了塌滑体在天然状态下处于极限平衡状态时的滑动方向,并使用其应力成果计算了塌滑体的三维安全系数;其次,建议了基于强度折减概念的三维加固安全系数计算方法:最后,提出了加固设计的进一步优化方案。计算结果表明,塌滑体的滑动方向与局部地形等高线近于垂直。主滑方向变化较大,自后缘的NE15°方向逐步过渡到中部的NS向,最终过渡到前缘的NE30°方向,以致很难作出能表征主滑方向的地质剖面。基于应力计算成果的安全系数计算公式不能充分考虑滑坡体的抗滑潜能,也不能充分反映滑坡体的滑动方向,安全系数偏大。基于强度折减概念的三维加固安全系数计算方法具有有限元等方法的优点,较好地克服了上述局限性,可以合理地评价加固后的滑坡稳定性。     

Rock slope stability and excavatability assessment of rocks at the Kapikaya dam site,Turkey

This paper presents the slope stability and excavatability assessment of rocks at the Kapikaya dam site that contains diabases. Both field and laboratory studies were carried out. The field study involved detailed discontinuity surveys. Laboratory tests were carried out to determine uniaxial compressive strength, Young's modulus, unit weight, point load strength index and shear strength parameters of discontinuities.Kinematical and numerical analyses were performed to determine right and left slopes at the dam site. According to kinematical analyses, the types of planar and wedge failure are not expected at the site. Also, shear strength reduction analyses was carried out using Phase² for the right and left slopes at the dam site. According to results of numerical analysis, Strength Reduction Factor (SRF) of the right and left slopes are 8.08 and 6.5 respectively and any rotational failure will not occur. The excavation category of the diabases was determined as easy ripping for the right slope and easy-hard ripping for the left slope.     

Rainfall thresholds for the triggering of landslides considering previous soil moisture conditions (Asturias,NW Spain)

Given its geological and climatic conditions and its rugged orography, Asturias is one of the most landslide prone areas in the North of Spain. Most of the landslides occur during intense rainfall episodes. Thus, precipitation is considered the main triggering factor in the study area, reaching average annual values of 960 mm. Two main precipitation patterns are frequent: (i) long-lasting periods of moderate rainfall during autumn and winter and (ii) heavy short rainfall episodes during spring and early summer. In the present work, soil moisture conditions in the locations of 84 landslides are analysed during two rainfall episodes, which represent the most common precipitation patterns: October–November 2008 and June 2010. Empirical data allowed the definition of available water capacity percentages of 99–100% as critical soil moisture conditions for the landslide triggering. Intensity-duration rainfall thresholds were calculated for each episode, considering the periods with sustained high soil moisture levels before the occurrence of each analysed landslide event. For this purpose, data from daily water balance models and weather stations were used. An inverse relationship between the duration of the precipitation and its intensity, consistent with published intensity-duration thresholds, was observed, showing relevant seasonal differences.     

Monitoring of coal mining subsidence in peri-urban area of Zonguldak city (NW Turkey) with persistent scatterer interferometry using ALOS-PALSAR

This paper presents the results of spatiotemporal monitoring of surface subsidence over a mining area in Zonguldak Province of Turkey using Synthetic Aperture Radar (SAR) data, providing maps of subsidence rates in the radar line of sight direction. A total of 18 SAR images, acquired between January 2007 and June 2010 by the Japanese Advanced Land Observing Satellite, have been used to map the surface displacements using the Persistent Scatterer Interferometry technique. The use of Phased Array Type L-band Synthetic Aperture Radar data has proved useful for avoiding signal decorrelation and estimating surface deformation in the heavily vegetated study region. The technique enables the monitoring of continuous small displacements over a large area. Our findings present that many Persistent Scatterers were located on the vegetation cover. The results reveal areas of ground surface subsidence up to 44 mm/year that are well correlated with the underground coal mining galleries particularly in the Gelik region where the Karadon mining galleries are present.     

Structural,geomorphological and geomechanical aspects of the Koyulhisar landslides in the North Anatolian Fault Zone (Sivas,Turkey)

. Recently, numerous landslides occurred in the northern part of Koyulhisar. In 1998 and 2000, which were very wet years, landslides in different masses affected the geological formations which are well known for being prone to slope movements. Detailed geological, geomorphological and geotechnical surveys were carried out, and stability conditions in Koyulhisar village, located NE of Sivas (Turkey), are discussed in this paper. Kinematical analyses showed that the potential slope instabilities are in two main directions: the first direction is SE and the second is SW, these directions corresponding to the dominant slope directions of the study area. Geomechanic surveys confirmed that most of the rock slopes analysed are highly prone to instability. The SMR criterion gave results which correspond well with real stability conditions. Jointing and faulting, steep topography, water incisions, and heavy rainfall played a significant role in the occurrence of the landslides.