Numerical analysis under seismic loads of soils improvement with floating stone columns     

Ferhat Şahinkaya  Mustafa Vekli  Cenk Cuma Çadır 《Natural Hazards》2017,88(2):891-917

Geotechnical Engineering has developed many methods for soil improvement so far. One of these methods is the stone column method. The structure of a stone column generally refers to partial change of suitable subsurface ground through a vertical column, poor stone layers which are completely pressed. In general terms, to improve bearing capacity of problematic soft and loose soil is implemented for the resolution of many problems such as consolidation and grounding problems, to ensure filling and splitting slope stability and liquefaction that results from a dynamic load such as earthquake. In this study, stone columns method is preferred as an improvement method, and especially load transfer mechanisms and bearing capacity of floating stone column are focused. The soil model, 32 m in width and 8 m in depth, used in this study is made through Plaxis 2D finite element program. The clay having 5° internal friction angle with different cohesion coefficients (c 10, c 15, c 20 kN/m²) are used in models. In addition, stone columns used for soil improvement are modeled at different internal friction angles (? 35°, ? 40°, ? 45°) and in different s/D ranges (s/D 2, s/D 3), stone column depths (B, 2B, 3B) and diameters (D 600 mm, D 800 mm, D 1000 mm). In the study, maximum acceleration (a _max = 1.785 m/s²) was used in order to determine the seismic coefficient used. In these soil models, as maximum acceleration, maximum east–west directional acceleration value of Van Muradiye earthquake that took place in October 23, 2011 was used. As a result, it was determined that the stone column increased the bearing capacity of the soil. In addition, it is observed that the bearing capacity of soft clay soil which has been improved through stone column with both static and earthquake load effect increases as a result of increase in the diameter and depth of the stone column and decreases as a result of the increase in the ranges of stone column. In the conducted study, the bearing capacity of the soil models, which were improved with stone column without earthquake force effect, was calculated as 1.01–3.5 times more on the average, compared to the bearing capacity of the soil models without stone column. On the other hand, the bearing capacity of the soil models with stone columns, which are under the effect of earthquake force, was calculated as 1.02–3.7 times more compared to the bearing capacity of the soil models without stone column.  相似文献   

Investigating water quality and arsenic contamination in drinking water resources in the Tavşanlı District (Kütahya,Western Turkey)     

Şehnaz Şener  Murat Karakuş 《Environmental Earth Sciences》2017,76(21):750

Arsenic is a natural component of the earth’s crust, and it is transported into surface water and groundwater through the dissolution of rocks, minerals and ores. In addition, arsenic leaching processes contaminate water sources and this geogenic arsenic contamination causes significant water quality problems in many parts of the world. In this study, water quality, arsenic contamination and human health risks of drinking water resources in the Tav?anl? District were determined and the origins were discussed. For this purpose, geological and hydrogeological properties were investigated. In situ measurements and chemical analyses were carried out on water samples taken from drinking water sources such as wells, springs and surface waters for hydrogeochemical studies. According to the obtained results, water resources are Ca–Mg–HCO₃, Mg–HCO₃ and Na–HCO₃ type. Total As (As_T) concentration of the water samples sometimes exceeds the permissible limit given by the TSI-266 (Standards for drinking waters, Turkish Standards Institution, Ankara, 2005) and WHO (Guidelines for drinking-water quality, World Health Organization, Geneva, 2008) for drinking water. H₃AsO ₃ ⁰ and HAsO₄ ^2? are dominant arsenic species in groundwater and surface water, respectively. Typically high total arsenic concentrations can be found in regions characterized by magmatic rocks. In addition, As concentrations in surface waters were found to be higher than in groundwater in the region, due to the anthropogenic influence of mining activities in the region.  相似文献   

Vertical spatial correlation length based on standard penetration tests     

Emir Ahmet Oguz  D. V. Griffiths 《Marine Georesources & Geotechnology》2019,37(1):45-56

The spatial correlation length (SCL), or the scale of fluctuation, is a parameter for describing the spatial variability of soil and one of the important parameters used in random field theory. Studies reporting the spatial correlation length based on real field data of offshore/nearshore sea bottom soils are rather limited in the literature, so in this study, the vertical spatial correlation length is determined using site investigation data from two sites of the southern coast of Turkey. Based on quite extensive data, the vertical spatial correlation length is estimated using four different autocovariance functions. The values are within typical ranges reported in the literature for similar soil groups, both onshore and offshore. It is also noted that the widely-used exponential function almost always gives the lowest value of spatial correlation length. The results of this study add to the database of spatial correlation lengths based on real data and could be useful for future studies on reliability assessment of offshore foundations using random finite element method.  相似文献   

Responses of the stratified flows to their driving conditions—A field study     

Yalcin Yuksel  Berna Ayat  Mehmet Nuri Ozturk  Burak Aydogan  Isikhan Guler  Esin Ozkan Cevik  Ahmet Cevdet Yalçıner 《Ocean Engineering》2008,35(13):1304-1321

The Bosphorus is oceanographically very complicated two-layer stratified strait where denser water from the Marmara Sea flows towards North under the lighter water which is frequently flowing from the Black Sea towards South. The water level difference between both ends of the Bosphorus varies seasonally within the range of ?0.2 and 0.6 m. The seasonal variability depends mainly on the water level changes in the adjacent basins related to the hydrological cycle, short-term changes in the atmospheric pressure and the wind characteristics. These variations together with the depth and alignment of the cross section along the strait dominate the spatial and temporal variations and sometimes sharp changes in the flow pattern in three dimensions. Although these hydrodynamic conditions are critical for all marine and hydraulic works along the Bosphorus, there was not continuous long-term measurement for a sufficient time span in the strait for detailed evaluation of the current climate. An extensive site surveying work including current, wind, pressure and water level measurements was carried out between September 2004 and January 2006 in relation to the design and construction requirements of the Bosphorus Tube Crossing Project. In this study, the characteristics of stratified flow in the Bosphorus Strait and their relation to local and regional, short- and long-term changes in the meteorological parameters are studied by using the measurement data and the results are discussed comparatively.  相似文献   

Impact of a new invasive ctenophore (Mnemiopsis leidyi) on the zooplankton community of the Southern Caspian sea     

Abolghasem Roohi  Zulfigar Yasin  Ahmet E. Kideys  Aileen Tan Shau Hwai  Ali Ganjian Khanari  Elif Eker‐Develi 《Marine Ecology》2008,29(4):421-434

The invasive ctenophore Mnemiopsis leidyi (Agassiz), which was transported from the Black Sea into the Caspian Sea at the end of the 1990s, has negatively affected the ecosystem of the Caspian Sea. Zooplankton abundance, biomass and species composition were evaluated on the Iranian coast of the Caspian Sea during 2001–2006. A total of 18 merozooplankton (13 species composed of larvae of benthic animals) and holozooplankton (four Copepoda and one Cladocera) species were identified. The total number of zooplankton species found here was 50% less than in a previous investigation performed in the same region in 1996 before the introduction of Mnemiopsis leidyi into the Caspian Sea. Cladocera species seemed to be highly affected by the invasion of Mnemiopsis leidyi; only one species, Podon polyphemoides, remained in the study area, whereas 24 Cladocera species were found in the study carried out in 1996. Whereas among the Copepoda Eurytemora minor, Eurytemora grimmi, Calanipeda aquae dulcis and Acartia tonsa that were abundant before the Mnemiopsis leidyi invasion, only A. tonsa (copepodites and adults) dominated the inshore and offshore waters after the invasion. The maximum in zooplankton abundance (22,088 ± 24,840 ind·m^?3) and biomass (64.1 ± 56.8 mg·m^?3) were recorded in December 2001 and August 2004, respectively. The annual mean zooplankton abundance during 2001–2006 was in the range of 3361–8940 ind·m^?3; this was two‐ to five‐fold less than the zooplankton abundance in 1996. During 2001–2006, the highest abundance and biomass of Mnemiopsis leidyi were observed during summer‐autumn months coincident with warm temperatures and generally when the abundance of other zooplankton organisms was low.  相似文献   

Annual cycle of zooplankton abundance and species composition in Izmit Bay (the northeastern Marmara Sea)     

Melek Isinibilir  Ahmet E. Kideys  Ahmet N. Tarkan  I. Noyan Yilmaz 《Estuarine, Coastal and Shelf Science》2008,78(4):739-747

The monthly abundance, biomass and taxonomic composition of zooplankton of Izmit Bay (the northeastern Marmara Sea) were studied from October 2001 to September 2002. Most species within the zooplankton community displayed a clear pattern of succession throughout the year. Generally copepods and cladocerans were the most abundant groups, while the contribution of meroplankton increased at inner-most stations and dominated the zooplankton. Both species number (S) and diversity (H′) were positively influenced by the increase in salinity of upper layers (r = 0.30 and r = 0.31, p < 0.001, respectively), while chlorophyll a was negatively affected (r = −0.36, p < 0.001). Even though Noctiluca scintillans had a significant seasonality (F_11,120 = 8.45, p < 0.001, ANOVA), abundance was not related to fluctuations in temperature and only chlorophyll a was adversely correlated (r = −0.35, p < 0.001). In general, there are some minor differences in zooplankton assemblages of upper and lower layers. A comparison of the species composition and abundance of Izmit Bay with other Black Sea bays reveals a high similarity between them.  相似文献   

Factors controlling the morphological evolution of the Çanakkale Strait (Dardanelles, Turkey)     

Erkan Gökaşan  Mustafa Ergin  Mustafa Özyalvaç  Halil İbrahim Sur  Hüseyin Tur  Tolga Görüm  Timur Ustaömer  Fatma Gül Batuk  Hakan Alp  Halim Birkan  Ahmet Türker  Erhan Gezgin  Murat Özturan 《Geo-Marine Letters》2008,28(2):107-129

Seismic profiling, bathymetric and physical oceanographic data collected from the Çanakkale Strait revealed that the morphological evolution of the strait has been controlled by tectonic activity, and sediment erosion and deposition. Sediments in the strait have been sourced mostly by rivers draining the Biga Peninsula during lowstand periods. In highstand periods, by contrast, deposits in the strait were reworked by currents. The seafloor morphology of the Çanakkale Strait is also controlled by a sequence of factors ranging from tectonics to current erosion and deposition. Channel deposits overlying the basement are being eroded at the narrower, meandering central section of the strait (the Nara Passage) due to high current velocities. The eroded sediments are deposited in the relatively linear and wider, northern and southern sectors of the strait exposed to low current velocities. As a result, the high-energy areas are more deeply incised due to the erosion, whereas deposition elevates the seafloor in the areas exposed to lower current energy. Three strike-slip faults, which possibly relate to the activity of the North Anatolian Fault Zone, are responsible for the irregular shape of the strait and this, in turn, controls the current velocity along the strait. The high-energy conditions probably commenced with the latest invasion of Mediterranean waters some 12 ka b.p., and have continued as a two-layered current system to the present day.  相似文献