UNDERSTANDING SHEAR WAVE VELOCITIES CORRELATIONS WITH N-SPT AND QC-CPT VALUES

Abstract eng:
Prediction of the ground shaking response at soil sites requires knowledge and understanding of soil shear wave velocity Vs, a parameter that is strongly related to small strain shear modulus Gmax. While it is preferable to measure soil parameters in situ, this is often not economically feasible at all locations. For this reason, and in order to improve correlations between geophysical measurements and key geotechnical parameters, this paper attempts to propose new general correlations between shear wave velocity Vs and SPT standard penetration resistance N as well as the CPT cone penetration resistance qc. The studied site is located on the Mediterranean coast, in the North Eastern suburb of Beirut, the capital of Lebanon, where the level of water is present near the ground surface. The variable near surface geological conditions throughout the city results in spatially variable ground shaking characteristics. In order to better understand seismic soil response, geotechnical data comprising both in situ and laboratory tests was gathered. This extensive data allows determining good correlations that may be validated by comparing the calculated shear wave velocity with previously obtained profiles from the inversion parameterization of dispersion estimates in order to derive shear-wave velocities (Vs) within each geological layer. In some relations, the depth factor D or effective stress σ’v and the corrected SPT-N60 were also introduced. The proposed relations are divided into three soil categories: sand, clay and all soils (mixed clay, sand and silt). The equations developed in this study compare very well with most of existing correlations in the literature. The proposed correlations are very important for both Lebanese and other soils, and may be used both in the design of a foundation system as well as in the assessment of soil behavior under earthquake loading conditions (Settlement and liquefaction, soil response...). These correlations should be used with caution in geotechnical earthquake engineering and should be checked against measured Vs.

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