Standard Penetration Test in Predicting the Shear Strength and the Cyclic Mobility of Fine Grained Soils

The evaluation of liquefaction susceptibility of soils and the related failures during earthquakes are one of the important aspects in geotechnical engineering. The liquefied soil will not only cause instability on substructure, but it will also cause failure on superstructure, resulting in catastrophic fatalities. Therefore, it is very important to be able to predict the liquefaction susceptibility of soils during earthquakes. There are different methods used for determining the liquefaction susceptibility of soils. In the present study, 20 boreholes in Basra city in Iraq were considered and the seismicity and the liquefaction susceptibility of the fine grained soils in these boreholes were studied by using the measured Atterberg limits, shear strength parameters and the standard penetration test, SPT N values. Because of the uncertainty and the confusion of the fine grained soils due to cyclic loading, the reliability of using the SPT values in predicting the Atterberg limits and the shear strength parameters of fine grained soils was also evaluated. According to the findings, Seed et al., (2003) and Bray et al., (2004) criteria’s were found to be more applicable for predicting the liquefaction susceptibility of Basra soil based on Atterberg limits data. The calculated factor of safety, FS against liquefaction based on cyclic stress ratio, CSR and cyclic resistance ratio, CRR gave a high liquefaction potential for Basra soil. Strong correlations between the shear strength parameters and the SPT values were obtained whereas for the prediction of cone penetration resistance, qc from SPT is not promising. Keywords: Chinese criteria, cyclic mobility, cyclic resistance ratio, cyclic stress ratio, liquefaction susceptibility, seismicity, sensitivity.