Browsing by Author "Akkaya, Ismail"

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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 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.