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Geotechnical investigation is a process in which the physical properties of a site are assessed for the purpose of determining which uses of the site will be safe. Geotechnical investigation is required before land can be developed or redeveloped. The goal of such investigation is to confirm that the land is safe to build on or to confirm the correct geotechnical rehabilitation methods for the existing buildings. The earthquake effect on existing buildings is important. Following the Kocaeli earthquake in Turkey, special soil investigation studies have been undertaken for highly important structures in order to decide on the necessity of retrofitting. It is known that, it is not always possible to make undertake in-situ testing to determine the shear wave velocity (Vs) in the urban area for small scale projects. Therefore, empirical correlations for shear wave velocity are gaining importance.
A study to determine site classification based on this investigation data is presented in this paper. In the case data set, there are no in-situ tests to determine the shear wave velocity. Empirical correlations from standard penetration tests (SPT) are used to determine the shear wave velocities (Vs) in the interpretative reports. In critical facilities, it is important to undertake geophysical testing to correctly determine site class, and to predict the building performances during an earthquake.
In this context, approximately one hundred boreholes are used. Initially, the standard penetration blowcount values (SPT-N value) are correlated to the shear wave velocities (Vs), then the site classification is determined based on U.S. Federal Emergency Management Agency (US - FEMA 356) standard (Table 1) and the standard of Specifications for Buildings to be Built in Earthquake Areas of Turkey (Turkey – DBYBHY). The soil classification results of both FEMA and Turkish standards are compared. Then direct SPT values are used to determine site class from tables presented in Specification for Buildings to be built in Earthquake Risk Areas in Turkey.
In conclusion, the effect of using different formulas to determine soil class is discussed. By determining the similarities and differences between the approaches, more accurate results can be attained in future soil classification studies.