A. B. Goktepe

Soil clustering by fuzzy c-means algorithm

In this study, hard k-means and fuzzy c-means algorithms are utilized for the classification of fine grained soils in terms of shear strength and plasticity index parameters. In order to collect data, several laboratory tests are performed on 120 undisturbed soil samples, which are obtained from Antalya region. Additionally, for the evaluation of the generalization ability of clustering analysis, 20 fine grained soil samples collected from the other regions of Turkey are also classified using the same clustering algorithms. Fuzzy c-means algorithm exhibited better clustering performance over hard k-means classifier. As expected, clustering analysis produced worse outcomes for soils collected from different regions than those of obtained from a specific region. In addition to its precise classification ability, fuzzy c-means approach is also capable of handling the uncertainty existing in soil parameters. As a result, fuzzy c-means clustering can be successfully applied to classify regional fine grained soils on the basis of shear strength and plasticity index parameters.

Cyclic Stress-Strain Behavior of Partially Saturated Soils

Although soils are generally assumed fully saturated below the groundwater table, they may be semi saturated near the state of full saturation under certain conditions. The situation of partial saturation may be caused by several factors, such as variation of water table level due to natural or manmade processes. It has been known in geotechnical engineering that the partial saturation of soil usually gives higher strength and lower compressibility. Additionally, it was shown in the recent studies that unsaturation of soil can also cause much greater amplification in ground motion then a fully saturated model and more resistance to liquefaction of sandy soils. Moreover, the resistance of sand to onset of liquefaction tends to increase with a reduction in the saturation ratio of soil specimens that was expressed in terms of the Skemptons pore pressure coefficient, B. Since the B-value is defined as the ratio of the induced pore water pressure to the applied effective confining stress, it can be simply obtained in the laboratory. The Skempton B-value method has been widely used to determine the state of saturation of laboratory soil specimens. In this study, in order to examine the stress-strain behavior and the strain softening response of partially saturated cohesive soil, a cyclic torsional shear apparatus were used, in which it was possible to perform cyclic shear tests on the specimens under undrained conditions. A series of the shear tests were conducted on the partially saturated-undisturbed clay samples. Therefore, the stress-strain properties were investigated to identify the saturation degree of near-saturated samples. Undisturbed clayey specimens were subjected to multi-staged cyclic torsional shear stress, and deformation characteristics of soils, such as the variations of the shear modulus and damping ratios were evaluated in terms of the saturation ratio. For the cyclic phase of torsional tests, the degradation curves were shown to move the right side with the decreasing Skempton B-value. It was also observed that initial values of the shear modulus were considerably affected the Skempton B-value.

Dependence of dynamic shear modulus of uniform sands on stress level and density

The first part of this study is a description and analysis of experimental investigations conducted to determine the nonlinear stress–strain behaviors of uniform sands when subjected to cyclic loadings at small strain levels. A series of torsional shear tests are performed under undrained conditions to analyze the variations in the stress–strain properties of saturated uniform sands consolidated to specified confining stresses and with certain relative densities. The role of effective confining pressure on the cyclic properties of isotropically consolidated sands is also considered. The second part of the study uses nonlinear multiple regression, neural network, and adaptive neuro-fuzzy inference methodologies to identify the complex mappings that range from void ratio and confining pressure input spaces to dynamic shear modulus output space. Test results and model comparisons are presented and evaluated in detail.