Yüksek plastisiteli killerin kalıcı kayma mukavemetine plastisitenin etkisi

Zeminlerde bir düşey gerilme altında deformasyonun artışıyla büyük şekil değiştirmeler sonrasında sabitkalan en düşük kayma gerilmesi değerine kalıcı kayma gerilmesi adı verilmektedir. Bu gerilme değerlerinegöre hesaplanan mukavemet ise kalıcı kayma mukavemeti (KKM) olarak tanımlanmaktadır. Özellikle aşırıkonsolide, sert ve fisürlü killerin gösterdiği gevrek davranış nedeniyle kayma mukavemetinde artandeformasyonla birlikte önemli derecede azalmalar görülmektedir. Kalıcı şartlara büyük yer değiştirmelersonucunda erişildiğinden geoteknik mühendisliğinde önceden kaymış ve tekrar aktif hale geçen şevlerinanalizinde önemli olmaktadır. Bu nedenle bu tür stabilite problemlerinin incelenmesinde veya tasarımdakalıcı kayma mukavemeti parametrelerine ihtiyaç duyulmaktadır. KKM parametrelerini laboratuvardabelirlemede yaygın olarak kullanılan deney yöntemleri Halka Kesme ve Tekrarlı Kesme Kutusudur. KKMparametrelerine mineraloji, efektif düşey gerilme, kesme hızı ve kil yüzdesi gibi birçok faktör etkiliolmaktadır. Burada etkiyen esas faktör zeminin mineralojik özellikleri olup, dolaylı olarak zemininplastisitesi ile KKM arasında ilişkinin varlığına işaret etmektedir. Bu çalışmada 31 farklı plastisiteözelliklerine sahip numune üzerinde Tekrarlı Kesme Kutusu ve Halka Kesme deneyleri yapılarak, KKMparametreleri belirlenmiştir. Konsolidometreler kullanılarak hazırlanan numunelerin tamamı yüksekplastisiteli kil (CH) sınıfında olup deneyler 0,02 - 0,03 mm/min kesme hızlarında ve en az üç farklı düşeygerilme altında gerçekleştirilmiştir. KKM'nin kıvam limitleri ile değişimi incelenmiş, pratik amaçlar içinkorelasyonlar geliştirilmiş, elde edilen bulgular önceki çalışmalarla karşılaştırılmıştır.

The effect of plasticity on residual shear strength for high plasticity clays

The minimum and constant value of shear stress attained at large displacements is defined as residual shearstrength (RSS) of soils. For especially over-consolidated fissured clays, as the shear deformation increases the shear stress firstly reaches to a peak value, and then gradually decreases to a constant value. RSS is usefulfor analyzing the pre-failed slopes in fissured clays and the progressive failures. Reversal Direct Shear andRing Shear Tests are well-known methods to obtain the RSS parameters in the laboratory. Previousinvestigations reveal that RSS is affected by mineralogy, effective normal stress and shear rate. As the mainaffecting parameter is mineralogy, a relationship between consistency limits and RSS could be established indirectly. In this study, Reversal Direct Shear and Ring Shear tests were carried out on 31 clay sampleshaving different plasticity characteristics to determine the RSS parameters. Tests were conducted at least at three different vertical stress levels at shear rates of 0.02 - 0.03 mm/min on the high plasticity clays (CH)samples prepared with slurry consolidometers. The variations of RSS parameters versus consistency limitswere studied. Some correlations were established for practical purposes and the findings were compared withthe previous studies.

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