Browsing by Author "Topal, Tamer"

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Assessment of the effectiveness of a rockfall ditch through 3-D probabilistic rockfall simulations and automated image processing
(ELSEVIERRADARWEG 29, 1043 NX AMSTERDAM, NETHERLANDS, 2021) Akin, Mutluhan; Dincer, Ismail; Ok, Ali Ozgun; Orhan, Ahmet; Akin, Muge K.; Topal, Tamer; AGÜ, Mühendislik Fakültesi, İnşaat Mühendisliği Bölümü; Akin, Muge K.
Rockfall ditches or catchment areas aim to collect falling blocks at the toe of a source zone by dissipating the energy of blocks in an excavated trench. The effectiveness of a rockfall ditch is simply expressed by its block catchment performance and can be evaluated by empirically using existing design charts as well as rockfall simulations. Although 2-dimensional (2-D) analysis has been executed to assess the catchment ditch effectiveness in engineering practice, 3-dimensional (3-D) rockfall models have not received enough attention so far. In this study, the effectiveness of a considerably long rockfall ditch to protect a settlement from falling rocks was assessed on the basis of 3-D rockfall analyses executed using high-resolution digital surface models. The rockfall ditch efficiency was found to be moderate to limited for various segments considering the percentage of blocks not trapped by the ditch. Moreover, the sensitivity of ditch efficiency to ditch depth was analyzed by automated image processing method as well. Additionally, a particular section of ditch alignment was fictitiously excavated or filled by synthetic Digital Surface Model (DSM) generation through image processing. 3-D rockfall modeling carried out using the DSMs with synthetically manipulated ditches points out that the effectiveness of a catchment ditch is highly depended upon ditch depth. Even a small volume of block accumulation inside the ditch definitely reduces the ditch performance resulting extended runout distances reaching to residential area. Finally, 3-D rockfall modeling is accepted to be an effective tool to rate the efficiency of existing rockfall ditches and synthetically generated ditches on DSMs (or DEMs) by means of automated image processing method may assist the control of current ditch dimension as well as new catchment ditch design.
Dynamic soil characterization and site response estimation for Erbaa, Tokat (Turkey)
(SPRINGERONE NEW YORK PLAZA, SUITE 4600 , NEW YORK, NY 10004, UNITED STATES, 2016) Akin, Muge K.; Kramer, Steven L.; Topal, Tamer; AGÜ, Mühendislik Fakültesi, İnşaat Mühendisliği Bölümü; Akin, Muge K.
Site amplification is one of the most important factors controlling damage in urban areas through strong earthquakes. Local site effects play an important role in earthquake-resistant design and should be considered for site response analyses. In this study, ground response analyses in Erbaa, Turkey, a settlement in the North Anatolian Fault Zone, using one-dimensional equivalent linear analysis and empirical approaches based on shear wave velocity profiles are evaluated and compared. The ground response analyses were performed with consideration of shear wave velocity, and modulus reduction and damping behavior for different confining pressure and plasticity index-dependent models. The results of ground response analyses and amplification values from empirical equations using shear wave velocity are illustrated in terms of amplification and predominant period maps of the seismically active Erbaa settlement area. The comparison has been made in these produced maps of the study area in order to evaluate different site response analyses.
Kaya tutma hendek performansının 3-boyutlu kaya düşme analizleriyle değerlendirilmesi: Akköy (Ürgüp) Örneği
(TMMOB - Jeoloji Muhendisleri Odasi, 2019) Akın, Mutluhan; Dinçer, İsmail; Orhan, Ahmet; Ok, Ali Özgün; Akin, Muge K.; Topal, Tamer; AGÜ, Mühendislik Fakültesi, İnşaat Mühendisliği Bölümü;
Rockfall ditches or areas can be constructed in order to protect against rockfalls in settlements that are in danger of rockfalls when the population density is not high. Nevertheless, in the design of such protection structures, essential site-specific engineering studies and analyzes are often not carried out appropriately. Therefore, rockfallditches are occasionally not capable of preventing rockfalls. Within the scope of this study, the performance of a 2 m-deep and 1 km-long rockfall ditch excavated at the upper elevation of touristic Akköy (Ürgüp) settlement in 2012 in order to prevent the entrance of falling rocks to the residential area was evaluated on the basis of 3-dimensional rockfall analyses. According to the rockfall risk classification, the settlement is under moderate rockfall risk. The digital surface model used in 3-dimensional rockfall analyses was generated by point cloud data obtained from photogrammetric images taken by unmanned aerial vehicle. During field observations, it was determined that the dimension of the previously fallen ignimbrite blocks could reach up to 2 m. On the other hand, the high persistency of discontinuities in the source zone indicates that the dimensions of the potential rockfall blocks may be large. As a result of the 3-dimensional rockfall analyses carried out in RocPro3D software, it was defined that the falling blocks are generally caught by the ditch excavated between the source zone and the settlement, but in some sections of the ditch those blocks may continue to roll over the rockfall ditch. Eventually, Akköy settlement is still partially under the danger of rockfalls. If the rockfall ditch is not periodically cleaned in the course of time, the extent of danger will enlarge with the decrease in the capacity of the trench. © 2019, TMMOB - Jeoloji Muhendisleri Odasi. All rights reserved.
Landslide Investigation of a Residential Area in Goynuklu Village, Bursa (Turkey)
(SPRINGER INTERNATIONAL PUBLISHING AGGEWERBESTRASSE 11, CHAM, CH-6330, SWITZERLAND, 2017) Topal, Tamer; Akin, Muge; Doyuran, Vedat; AGÜ, Mühendislik Fakültesi, İnşaat Mühendisliği Bölümü
Landslide is a natural process of the earth's surface, inevitably resulting from gravity with many triggering factors such as rainfalls, earthquakes, slope steepening, removal of vegetation, etc. The most frequent landslide-triggering mechanism is water from intense rainfall or human-based sources. The wide ranges of landslides and the complexity and variability of their interactions with the environment are the key points of a landslide investigation. The rate of the movement is the main factor of high property damages. On 16th of March in 2006, a rapid landslide occurred in Goynuklu village in Bursa, Turkey. The properties were inevitably damaged after the failure. The triggering factors of the failure mechanism and the properties of the landslide were investigated to specify proper remedial measures at the site. The geotechnical investigations including surface and subsurface studies were performed to determine the extent of the landslide and its sliding surface accurately. Within the framework of the geotechnical investigations, the inclinometer measurements were also recorded after drilling boreholes. Besides, a number of trial pits were excavated for evaluating the shallow sliding surfaces. Samples taken from the boreholes and trial pits were tested in the laboratory to obtain the soil class and the distribution of the grain size of the soil layers as well. The field tests including the hydraulic effect on the soil layers were also resolved by means of in situ permeability tests. Based on the data obtained, the characteristics and mechanism of the landslide were analyzed. The landslide occurred on a translational sliding surface in Neogene sediments including non-stratified sandstone-siltstone-claystone layers and a landfill site in a residential area. The shear strength characteristics of the sliding surface were calculated by back-analyses.
A new quantitative welding degree classification for ignimbrites
(SPRINGER, 2023) Akin, Mutluhan; Topal, Tamer; Dincer, Ismail; Akin, Muge K.; Ozvan, Ali; Orhan, Ahmet); Orhan, Ayse; 0000-0001-8873-5287; AGÜ, Mühendislik Fakültesi, İnşaat Mühendisliği Bölümü; Akin, Muge K.
As a pyroclastic rock type, ignimbrites may reveal varying degrees of welding depending on the temperature (>535 ℃) and overburden pressure conditions during its formation. The welding degree of ignimbrites increases as the formation temperature and the thickness of the overburden deposit in the depositional environment escalate, which are the most crucial factors controlling the rate of welding in ignimbrites. With the increasing temperature, plastic deformation is observed in ignimbrites and the glassy minerals are being welded. Furthermore, the thickness of the overburden causes the deformation of the ash matrix in ignimbrites at the lower sections and the pumice grains are fattened at diferent rates. An increase in the degree of welding of ignimbrites causes an improvement in the physical and mechanical properties of the rock material as well. Within the scope of this research, petrographical, mineralogical, and geochemical studies were carried out on a total of 16 diferent ignimbrite types, which have diferent color and texture properties, obtained from three diferent regions of Turkey (Kayseri, Nevşehir, Ahlat) where ignimbrites extensively crop out, and the physical and mechanical properties of these samples were revealed. Consequently, a new welding classifcation was developed for ignimbrites considering the uniaxial compressive strength and dry unit weight. The proposed welding classifcation consists of six classes ranging from non-welded to highly welded. When the welding degrees of the selected ignimbrites are evaluated, Kayseri ignimbrites mostly exhibit moderate welding characteristics. Nevşehir ignimbrites, on the other hand, have a low welding degree whereas the degree of welding in Ahlat ignimbrites may vary from low to high. Additionally, long and short axis lengths of pumice grains in the ignimbrite specimens were determined by measuring under the microscope, and shape ratios were determined by diferent shape parameter evaluation methods. As a result, it has been concluded that the pumice grains in Kayseri and Ahlat ignimbrites have a more lenticular structure than the pumice grains in Nevşehir ignimbrites. Eventually, the welding degree classes of ignimbrites and the classifcation developed by using threshold values of the oblateness ratio (OR) values of pumice grains at diferent welding degrees are quite compatible. The proposed welding degree classifcation is of great importance in the selection of ignimbrites widely used as dimension stone and in terms of engineering classifcation of this rock type as well as it will guide to the scientifc studies to be performed on ignimbrites with varying physical and mechanical properties.
Rockfall Hazard Assessment Around Ankara Citadel (Turkey) Using Rockfall Analyses and Hazard Rating System
(SPRINGER, VAN GODEWIJCKSTRAAT 30, 3311 GZ DORDRECHT, NETHERLANDS, 2020) San, Nyein Ei; Topal, Tamer; Akin, Muge K.; 0000-0001-8873-5287; AGÜ, Mühendislik Fakültesi, İnşaat Mühendisliği Bölümü
Ankara Citadel which is one of the important cultural heritages in Turkey settles in the oldest part of Ankara. Rockfall event has occurred around the Citadel located on a steep hill where andesite is exposed. The rockfall problem causes a great risk to the surrounding area where road, school, floral shops, car parking. Therefore, the major aim of this research is to reveal the rockfall risk around the castle. The rockfall problems around the Ankara Citadel may be linked with weathering, freezing-thawing, earthquake, and cooling joints, and effects or combination of these in the rock units. The rockfall-related hazard at the Citadel is assessed by 2-D rockfall analyses along several profiles in this investigation. Field observations and stability analyses (kinematic and limit equilibrium) of the slopes reveal that there exist many blocks ready to fall down. Four different andesite block sizes measured in the field are separately analyzed on the basis of bounce height, fall-out distance, velocity and kinetic energy of the blocks. The obtained data are evaluated to define the possible rockfall-based hazard zones. Based on the danger zones acquired from the rockfall analyses, the removal of the fallen and loosen andesite blocks and the installation of catch barriers with suggested properties are recommended. Besides, the risk integrated into rockfall hazard rating system on the basis of structural and morphological criteria of the rock mass reveals that medium risk category to be mitigated by light remedial measures for the indicative protection exists in the study area.