Browsing by Author "Akin, Mutluhan"

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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.
Comparison of SPT and V-s-based liquefaction analyses: a case study in Ercis (Van, Turkey)
(SPRINGER INTERNATIONAL PUBLISHING AG, GEWERBESTRASSE 11, CHAM, CH-6330, SWITZERLAND, 2018) Akkaya, Ismail; Ozvan, Ali; Akin, Mutluhan; Akin, Muge K.; Ovun, Ugur; 0000-0002-7682-962X; 0000-0001-8873-5287; AGÜ, Mühendislik Fakültesi, İnşaat Mühendisliği Bölümü
Liquefaction which is one of the most destructive ground deformations occurs during an earthquake in saturated or partially saturated silty and sandy soils, which may cause serious damages such as settlement and tilting of structures due to shear strength loss of soils. Standard (SPT) and cone (CPT) penetration tests as well as the shear wave velocity (V-s)-based methods are commonly used for the determination of liquefaction potential. In this research, it was aimed to compare the SPT and V-s-based liquefaction analysis methods by generating different earthquake scenarios. Accordingly, the Ercis residential area, which was mostly affected by the 2011 Van earthquake (M-w = 7.1), was chosen as the model site. Ercis (Van, Turkey) and its surroundings settle on an alluvial plain which consists of silty and sandy layers with shallow groundwater level. Moreover, Caldiran, Ercis-Kocapinar and Van Fault Zones are the major seismic sources of the region which have a significant potential of producing large magnitude earthquakes. After liquefaction assessments, the liquefaction potential in the western part of the region and in the coastal regions nearby the Lake Van is found to be higher than the other locations. Thus, it can be stated that the soil tightness and groundwater level dominantly control the liquefaction potential. In addition, the lateral spreading and sand boiling spots observed after the 23rd October 2011 Van earthquake overlap the scenario boundaries predicted in this study. Eventually, the use of V-s-based liquefaction analysis in collaboration with the SPT results is quite advantageous to assess the rate of liquefaction in a specific area.
Impact of Jet-Grouting Pressure on the Strength and Deformation Characteristics of Sandy and Clayey Soils in the Compression Zone
(KOREAN SOCIETY OF CIVIL ENGINEERS-KSCE, 3-16 JUNGDAE-RO 25-GIL, SONGPA-GU, SEOUL, 05661, SOUTH KOREA, 2019) Akin, Mutluhan; Akkaya, Ismail; Akin, Muge K.; Ozvan, Ali; Ak, Yusuf; 0000-0002-7682-962X; 0000-0001-8873-5287; AGÜ, Mühendislik Fakültesi, İnşaat Mühendisliği Bölümü
Jet-grouting as a soil improvement method is extensively preferred in today's civil engineering practice. High-modulus grout columns constructed by extremely high jetting pressures displace the surrounding soil causing a densification in soil particles. Accordingly, the strength as well as the deformation characteristics of subsurface soils are relatively improved across the compression zone which is under the influence of high jetting pressure. In this study, the modification of soil properties in compression zone after jet-grouting in sandy and clayey soils is investigated by standard penetration tests (SPT) and multi-channel analysis of surface waves (MASW) performed at a couple of construction sites along established jet-grout column rows. The in-situ test results point out significant improvement of the measured parameters compared to initial values. The rate of enhancement in the compression zone is higher in sandy strata than that of clayey deposits. The strengthening of soil due to jetting pressure is validated by finite element analyses as well. Furthermore, very low shear strain values are obtained in clayey soils with respect to the improved characteristics of compression zone representing extremely low shear deformation under foundation.
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.
A study of the relationship between the pressuremeter modulus and the preconsolidation pressure around a thrust fault
(SPRINGER, 233 SPRING ST, NEW YORK, NY 10013 USA, 2019) Ozvan, Ali; Ozvan, Elif E.; Akkaya, Ismail; Akin, Mutluhan; Akin, Muge K.; 0000-0002-7682-962X; 0000-0001-8873-5287; 0000-0001-5459-3989; AGÜ, Mühendislik Fakültesi, İnşaat Mühendisliği Bölümü
The study area is in a zone under the influence of the Lake Van water changes and the Van fault, which caused a destructive earthquake in 2011. Due to the level changes of Lake Van, sediments with different thicknesses as well as grain sizes were deposited in this region and the characteristics of these sediments were significantly affected by the morphology and lake water fluctuations in the past. A total of six boreholes were drilled along a 3-km line within the study area to determine the preconsolidation pressure (sigma(pc)) and the pressuremeter test values of the clayey levels of old lake deposits-which are known to have different physical and mechanical properties-with hopes to gain an insight on how they influence the mechanical tests performed in the field and in laboratory conditions. The relationship between these values was also statistically evaluated. When both datasets were evaluated together, it was determined that the stresses in the area close to the Van Thrust Fault plane caused deformations in the soil, which in turn affected the hanging-wall block of the thrust fault in particular. The inspection of E-M and sigma(pc) values for the area within the primary compression zone of the Van Fault revealed that both values of the boreholes on the footwall block were higher compared to other boreholes close to the lake (southwest). This finding indicates that the fault stresses at the footwall block of the fault plane enhance the mechanical characteristics of the soil. The data obtained were also evaluated using regression analysis. Relationships between all available data were investigated and a high coefficient of determination was derived between the Menard deformation modulus (E-M) and the preconsolidation (sigma(pc)) pressure.