The Consolidation Behavior of the Clay-Core in a Rock Fill Dam — Atatürk Dam Case Study

Unexpectedly large settlements occurred in the 165 meter high clay core of Atatürk Dam during the reservoir filling stage. An investigation was conducted based on laboratory experiments and numerical analysis. Consolidation tests were performed on compacted samples under stress levels expected to take place in the field by considering the possible factors affecting the consolidation behavior. The experimental findings were used to model the observed settlements based on a parametric study and by back-calculation. The total expected settlements were determined to be in the order of 16.0 m. While a good fit was captured between the observed and modeled settlements prior to the reservoir filling, it was not possible to model the significantly large settlements observed within the clay core located approximately 120 meter below the crest following the reservoir filling. Evaluating other observations and findings, it was concluded that this phenomenon could be attributed to the lateral displacement of the core material into the filter and shell zones that were prone to instabilities due to disintegration under water

Micromechanism-based endochronic modeling of sand behavior

Mikroskobik değişkenlerin ve bunların şekil değişimi ile birlikte değişimlerinin belirlenmesi ve tanecikli ortama ait bu değişkenlerle sürekli ortam arasındaki bağlantının sade ve basit bir şekilde kurulması oldukça önemli ve büyük bir sorundur. Bu çalışmada, mikroskobik sürece ait içsel durum değişkenlerine dayalı olması ve sürekli ortamda tanımlanabilen bünye ifadelerine olanak vermesinden dolayı, endokronik teorinin olanakları geliştirilmeye çalışılmıştır. Zemin davranışının mikro ölçekte gerçekleşen sürecinin anlaşılması amacıyla, ilkin, hangi mikro ölçek değişkenlerinin zemin davranışını izah edebileceği tartışılmıştır. Daha sonra, zeminlerin şekil değiştirmesinin mikromekanizması bir seri sava bağlı olarak izah edilerek, endokronik bünye ifadeleri elde edilmiştir ve önerilen modelin öngörü kapasitesi drenajlı üç eksenli basınç koşulları için irdelenmiştir. Anahtar Kelimeler: Zemin modelleri, kum, mikromekanizma, endokronik model.The observed macroscopic properties of soil behaviour is mainly the manifestation of microscopic mechanism during deformation. Consequently, modeling of soil behaviour should ideally be based on the microscopic process determining the behaviour. But, observation and determination of the related microscopic properties and parameters is a difficult and time consuming process. Besides this problem, the link between the microscopic particulate medium and continuum medium is an another problem and usually very complex relations have been proposed. One of the main advantage of endochronic theory is its fundamental philosophy which bases the phenomenology of the soil behaviour on the internal state variables that need not to be observed. The first part of this study focuses on the arguments related with micro variables that are supposed to be controlling macroscopic soil behaviour. It is aimed to determine the important micro variables and consequently to propose a general hypothesis about the micromechanism of deformation process in sands. Regarding to the perspective gained by the proposed hypothesis for the micromechanism of soil deformation, constitutive relations are obtained and the predictive capacity of the proposed model is investigated by modeling of drained triaxial tests conducted on sands. It has been seen that stress-strain behaviour can well be modelled while observed softening phenomena still needs to be more clearly formulated in the model.  Keywords: Soil Models, sand, micromechanism, endochronic model.

Field Evidence and Laboratory Testing of the Cyclic Vulnerability of Fine-Grained Soils During the 1999 Kocaeli Earthquake

Significant earthquake-induced settlements occurred in saturated fine-grained soils at the Carrefour Shopping Center in Turkey during the 1999 Kocaeli Earthquake (M=7.4). Most of the settlement was due to the undrained cyclic failure of silt/clay (ML/CL) and highplasticity clay (CH) strata within the subsoil profile. Each suffered about 1% vertical strain. Extensive laboratory testing on undisturbed samples from these silty and clayey strata has been performed to investigate this behavior. The laboratory testing included monotonic and cyclic simple shear tests, triaxial tests and conventional 1-D consolidation tests. Considerable pore pressure increases have been measured during cyclic simple shear test which was later followed by significant reconsolidation settlement. It was found that significant pore pressures begin developing in these soils at cyclic stresses at about 50% of their monotonic shear strength. This transition in behavior with high pore pressure development and subsequent post-cyclic volume changes corresponds to about 0.5% cyclic shear strains. The study demonstrates the limitations of generalized liquefaction screening methods, and dispels the common misconception that high plasticity soils cannot generate high pore pressures and fail under cyclic loading. Test results indicate that the soils at the site can generate significant pore pressures when shaken at levels expected to have occurred during the Kocaeli Earthquake. The findings from this study are inline with the limited number of studies on this topic. Fine-grained soils, if shaken hard enough, can suffer strength loss and reconsolidation settlements. The challenge remains to better understand such phenomenon and incorporate this into engineering practice. This paper presents the observed ground failure at the site, site characterization studies and following laboratory testing program