Abdulazim Yildiz

Numerical analyses of embankments on PVD improved soft clays

In this paper, three-dimensional behaviour of an embankment on soft soils incorporating prefabricated vertical drains is analysed with finite element method using a recently proposed constitutive model, namely S-CLAY1S. The constitutive model accounts for plastic anisotropy, interparticle bonding and degradation of bonds. The numerical simulations show that neglecting effects of anisotropy and destructuration may lead to inaccurate predictions of soft clay response. The same problem is also analysed under two-dimensional plane strain conditions. Axisymmetric vertical drains are converted into equivalent plane strain conditions using three different numerical matching techniques purposed in the literature. In order to validate these matching techniques, the 2D equivalent plane strain results are compared with the results of 3D analysis. It is shown that these numerical matching techniques accurately predict the consolidation behaviour of an embankment on PVD improved soft clays and provide a useful tool for engineering practice.

Field Test of Circular Footings on Reinforced Granular Fill Layer Overlying a Clay Bed

The ultimate bearing capacity and settlement of a circular shallow rigid plate on compacted granular fill layer with and without geogrid reinforcement overlying on natural clay deposit exhibiting low bearing capacity and large settlement have been investigated. A total of 15 field tests were carried out using a circular model rigid plate with a diameter of 0.90 m. This study has been initially directed to evaluate the beneficial effects of the compacted granular fill layer on natural clay deposit for the shallow rigid plate performance. Then, the reinforcing effect of the top granular fill layer with horizontal layers of welded geogrid reinforcement on the bearing capacity and settlement has been studied. Parameters of the testing program include granular fill thickness, depth of first reinforcement, vertical spacing of reinforcement layers, and number of reinforcement layers. Bearing capacity ratio (BCR) and percentage reduction in settlement (PRS) were defined to evaluate improvement performance. Based on the test results, the effect of the granular fill and welded geogrid reinforcement on the bearing capacity and settlement are discussed. The results indicate that the use of granular fill layers over natural clay soils has considerable effects on the bearing capacity and settlement characteristics. The construction of granular fill layer with welded geogrid reinforcement over clay deposit helps in redistributing the applied load to a wider area. It has been observed that the use of welded geogrid reinforcement in granular fill layer provides additional improvement of bearing capacity and provides reduction in settlement of the rigid plate up to 80 and 60 %, respectively.

Yumuşak Zemin Model Parametrelerinin Zemin Davranışına Etkisi

Kil gibi yumusak zeminler yuksek poroziteye sahiptir ve diger zemin turleri ile karsilastirildigi zaman yuksek sikisabilirlik gostermektedir. Odometre deneyinde, normal konsolide killer normal konsolide kumlara gore on kat daha yumusak davranmaktadir [1]. Kil zeminler cok dusuk permeabiliteye sahiptir ve permeabilite konsolidasyon oraninin idaresinde oldukca onemlidir. Bu calismada ilk olarak yumusak kilin birincil konsolidasyon davranisi buyuk olcekli bir laboratuvar oedometre deneyi kullanilarak incelenmistir. Yumusak kili temsil etmesi icin yeniden yapilandirilmis kaolin kili kullanilmistir. Kaolin tozu likit limitin 1,5 kati kadar su ile karistirilarak 30kPa degerinde bir eksenel basinc ile konsolide edilmistir. Calismanin ikinci kisminda, klasik laboratuvar deneylerinden elde edilen zemin parametrelerinin, yumusak zemin davranisina etkisi Plaxis 2D sonlu eleman hesaplari ile arastirilmistir. Sonlu eleman hesaplarinda Yumusak Zemin Modeli kullanilmistir ve model parametreleri standart laboratuvar deneylerinden elde edilmistir. Simulasyonlar uygun model parametrelerinin belirlenmesinin yumusak zemin davranisinin modellenmesinde oldukca buyuk bir oneme sahip oldugunu gostermektedir.