Turgay BEYAZ, Kamil KAYABALI, Yetiş Bülent SÖNMEZER

Kumların sıvılaşmasında rölatif sıkılık ve kesme birim deformasyonu etkisinin incelenmesi

Kohezyonsuz zeminlerin sıvılaşma potansiyeli, gerilme yaklaşımını kullanan SPT, CPT gibi arazi yöntemleri ve üç eksenli dinamik kesme, burulmalı kesme, rezonant kolon, bender eleman gibi laboratuvar deneyleri ile belirlenmektedir. Kumların sıvılaşma potansiyelinin tahmininde son zamanlarda, enerji kavramı kullanılmaya başlanmıştır. Bu yaklaşımda kullanılan başlıca parametreler, zeminin rölatif sıkılığı ve efektif gerilmedir. Bu çalışmada, Devirsel Basit Kesme Düzeneği kullanılmıştır. Bu çalışmada, kumların sıvılaşma enerjisinin belirlenmesinde, kesme birim deformasyonu oranı ve rölatif sıkılığın etkisi incelenmiştir. Çalışmada, temiz ince deniz kumu kullanılmıştır. Kum numuneleri 3 farklı rölatif sıkılıkta (Dr=%40, %55 ve %70); 4 ayrı düşey gerilme (σv= 50, 100, 200 ve 300 kPa) ve boşluk suyu basıncı (u= 25, 50, 75 ve 150 kPa) etkisinde bırakılmıştır. 3 ayrı kesme birim deformasyonu oranında (?= %2, %3.5 ve %5) toplam 36 deney yapılmıştır. Deney örneklerine, tek eksenli 0.1 Hz frekansta harmonik yükleme uygulanmıştır. Çalışma sonucunda rölatif sıkılık, kesme birim deformasyonu oranı ve düşey gerilme şartlarının kumların sıvılaşma potansiyeline etkisi ince taneli deniz kumu için ortaya konmuştur. Kesme birim deformasyon oranındaki artış, sıvılaşma potansiyelini %3’lük oranda azaltmaktadır. Rölatif sıkılıktaki artış, kumun kesme direncini arttırmaktadır. Bu ise sıvılaşmayı geciktirmekte ve devir sayısında artışa neden olmaktadır.

Anahtar Kelimeler:

Devirsel basit kesme deneyi, Boşluk suyu basıncı, Kesme birim deformasyonu, Sıvılaşma potansiyeli, Düşey gerilme, Rölatif sıkılık

Investigation of the effect of the relative density and shear strain on liquefaction of sands

Liquefaction potential of non-cohesive soils is determined by field tests such as SPT, CPT, which use the stress approach, and laboratory tests such as three-dimensional dynamic shear, torsional shear, resonant column, and bender element tests. Recently, the approach of energy has been used to estimate the liquefaction potential of sands. The main parameters used in this approach are relative density and effective stress of the ground. In this study, Cyclic Simple Shear Test arrangement is used. In this study, the effect of shear strain and relative density on the liquefaction energy of the sands were investigated. In the study, clean fine marine sands were used. In this study, 3 different relative densities for a sand sample (Dr= 40%, 55% and 70%); 4 different stresses (σv= 50, 100, 200 ve 300 kPa), and pore water pressure (u= 25, 50, 75 ve 150 kPa). Totally of 36 experiments were performed in and 3 different deformation rates (γ= 2%, 3.5%, and 5%). The harmonic loading was applied to the experimental samples at a frequency (f) of 0.1 Hz. The effect of relative density, deformation rate and vertical stress conditions on the liquefaction energy of sands has been demonstrated for a type of fine-grained clean sea sand. The increase in the shear strain rate reduces the liquefaction potential by about 3%. The increase in relative density, increases the shear resistance of the sand. This delay liquefaction and causes an increase in the number of cycles.

Keywords:

Cyclic simple shear test, Pore pressure, Shear strain, Liquefaction potential, Vertical stress, Relative density,

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