A sudden slope failure occurred in Manisa possibly due to the effect of water infiltration because of a slightly damaged sewage pipe. Considering that there was no other evidence such as rainfall or any loading conditions to trigger the slope failure, a laboratory investigation on the soil’s unsaturated hydro-mechanical properties was initiated. Slopes are naturally unsaturated soils, and they may lose their stability with increased saturation degrees with water infiltration. Thus, for a proper investigation, the unsaturated hydro-mechanical properties of soils should be determined. The results presented in this study are focused on determining the key parameters to evaluate the slope failure for unsaturated soil conditions. In this regard, hydraulic conductivity and suction characteristics and the shear strength parameters were determined as well as the classical geotechnical properties of the soil. Classification of soil was determined as silty sand which is known to have slight to moderate suction stresses and mostly affected suddenly by water infiltration. A flexible-wall permeability test was run with a falling head procedure and the saturated hydraulic conductivity of the soil sample was measured as 1x10-7 m/s. Suction characteristics were detected by filter paper method, besides, the soil water retention curve of the soil was constructed. The maximum matric suction of the soil was measured as 2887 kPa for an air-dried sample. Following, the shear strength parameters were measured by conventional direct shear test for both dry and soaked conditions. Finally, the friction angle due to suction was calculated to be 1.7 degrees from the results of dry and saturated shear strength parameters.

Coarse soils can contain flaky grains in addition to rounded or angular grains, along with a varying fines content. Depending on the regional geology, however, the mica grain content can be remarkable, reaching 30 % or higher. Therefore, it is reasonable to expect that mica grains would affect the soil behaviour. In this study, soils of a delta deposit that are known to involve mica grains were examined. The river sand was considered as the host material and the mica grain contents were determined by means of the flotation technique. A correlation between the mica content as found using the flotation technique and XRD count numbers obtained using an X-ray diffraction test method for each soil sample was established. The standard penetration test (SPT) blow counts from various boreholes were interpreted from the mica content’s influence point of view. The results showed that the mica grains would reduce the SPT resistance at certain fines-content, host-sand, mica-grain combinations. The reduction in the SPT resistance as a result of the presence of mica grains might reach eight units at depths close to the ground surface. This influence is expressed by means of a dimensionless parameter (MCef); however, it diminished with an increasing effective stress and fines content. The findings of the present study show that the influence of particle shape on the overall soil behaviour deserves further study.

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Türkiye ve dünyanın birçok yerleşim yeri deprem tehdidi altındadır. Deprem neticesinde suya doygun ve gevşek kumlu zeminlerde sıvılaşma olayı meydana gelebilmekte buna müteakip yapıların temellerinde taşıma gücündeki aşırı azalma ya da zeminin akması ve yüksek deformasyonu neticesinde geniş bir alanda birçok yapıyı aynı anda etkileyebilecek zeminden kaynaklı kayma, göçme, aşırı otuma, eğilme, devrilme gibi hasarlar meydana gelebilmektedir. Bu tür zeminler Türkiye, Avrupa ve dünyanın birçok yerinde marjinal zemin davranışı gösteren zeminler olarak tanımlanmaktadır. Marjinal zeminlerde yer alan yapıların tasarımı için sahaya özel deprem tepki analizleri önerilmektedir. Aynı zamanda sıvılaşma gibi davranışa sahip olabilecek marjinal zeminlerde enjeksiyon ve jet-grout gibi zemin iyileştirme ve güçlendirmeleri uygulanmaktadır. Bu tür sıvılaşma potansiyeli olan ve iyileştirme ya da güçlendirme uygulanmış zeminlerde yapı tasarımı için güçlendirme öncesi ve güçlendirme sonrası zemin durumunun (sınıfının) dikkate alınması hususunda fikir ayrılıkları olabilmektedir. Bu çalışmada sıvılaşma potansiyeline sahip bir zemin profili için güçlendirme öncesi ve güçlendirme sonrası için sahaya özel zemin tepki analizleri yapılmış ve sonuçları karşılaştırmalı olarak takdim edilmiştir. Ele alınan problemde yapı temel taban seviyesinden (-5m) itibaren sıvılaşma bölgesi içinde 15 m’lik -20 m seviyesine kadar jet-grout uygulaması ile güçlendirme yapılmıştır. Zemin tepki analizlerinin yapıldığı saha için alüvyon istifinin kalınlığı ise 150 m civarındadır. Bu çalışma sonucunda burada verilen örnek uygulamada olduğu gibi alüvyon istifinin kalın olduğu durumlarda alansal ve derinlik bakımından sınırlı bir bölgede yapılan zemin güçlendirmelerinin dinamik zemin tepki analizleri üzerinde etkisinin nispeten düşük ve sınırlı kaldığı görülmüştür.

In this paper, the deep excavation stages of Poligon Station which is the located along the Üçyol–Fahrettin Altay subway line was modeled numerically. Although some parts of the metro line were constructed, some parts of metro line are currently under construction in İzmir. The Poligon Station is carried out with a surrounding diaphragm wall and top-down construction method. The foundation mat and four slabs of the station building are used as support elements. The excavation depth of the station is 18 meters. The soil properties of the numerical model were obtained engineering boreholes and laboratory tests. Lateral soil displacements were measured with inclinometers installed in the nearby soil layers. Displacements which were measured from inclinometers and obtained from numerical modeling were compared. Beside the static analysis, the Poligon station of the metro line was analyzed with a model earthquake. 16.12.1977 İzmir Earthquake (Ms=5.5, amax=0.21g) was used as a model earthquake for dynamic analyses. In addition, effects of changing the properties of the soil on computed results were numerically investigated using the software Plaxis.