Ground Failures Under Seismic Conditions PDF Download

The August 17, 1999, Kocaeli, Turkey earthquake (Mw = 7.4) struck the northwestern region of the country and was one of the most deadly and costly earthquakes of the country's modern history. Ground failure in Adapazari was particularly severe. Besides pervasive structural damage, hundreds of buildings settled, tilted, and translated horizontally over their foundations. Ground failure was observed predominantly directly adjacent to buildings. The primary goals of this dissertation are to explain the causes of the ground failures and their resulting effect on building performance in Adapazari. The investigation focuses initially on: 1) the characterization of the buildings at twelve sites where ground failure was observed, and 2) the characterization of the subsurface soil conditions that exist under the foundation of these buildings. The subsurface investigation program included Cone Penetration Test (CPT) soundings and carefully performed soil borings with the implementation of the Standard Penetration Test (SPT). The energy imparted to the system by the drop of the hammer during the SPT was measured to obtain accurate values of N6o. Additionally, the observations at areas of the center of the city where ground failure did and did not occur after the Koceali earthquake were correlated with the liquefaction susceptibility of the subsurface soils. The in situ testing program found that the soils that led to severe building damage are shallow, Holocene, low to medium plasticity alluvial silts. The response of these soils to earthquake shaking is less understood than that of clean sands. Thus, the second task of this investigation was to obtain representative "undisturbed" specimens of these soils and test them under cyclic loading in the laboratory. This required establishing a cyclic triaxial device in Turkey to avoid the disturbance associated with shipping soils back to the USA. The results of a large number of cyclic tests (primarily triaxial with some simple shear) showed that the current state-of-the-art method for evaluating liquefaction susceptibility of fine-grained soils, i.e. the Chinese Criteria, is not reliable. A new procedure for the identification of fine-grained soils susceptible to liquefaction and cyclic mobility based on the soil's plasticity index and liquid limit to water content ratio was developed. The results of the cyclic tests were also used to evaluate the liquefaction triggering potential of Adapazari silt. The results of this analysis were compared with those obtained from the use of in situ tests, and were found to be generally consistent. The additional confinement and loading of the buildings in Adapazari were found to significantly reduce the shallow silt's resistance to liquefaction and increase the shear strain induced by the earthquake. The ground motions to which the buildings in downtown Adapazari might have been subjected to and the possible mechanisms that led to the observed building performance are explained in a general framework.