| Large design earthquake ground motions (e.g., PGA values ranging up to 1.0 g and greater) are encountered in Northwest Arkansas. These large ground motions are problematic when coupled with the unknown seismic response of the deep, soft soils encountered in the Mississippi Embayment. Based on empirical standard penetration test (SPT) liquefaction triggering analyses, many soils in this area exhibit apparent liquefaction susceptibility at depths greater than 30 m (100 ft). In order to help evaluate potential liquefaction susceptibility of deep soil deposits in the Mississippi Embayment, the three most commonly used SPT-based liquefaction triggering procedures (Youd et al. 2001, Cetin et al. 2004, and Idriss and Boulanger 2008) have been examined, systematically compared, and programmed into user-friendly Excel workbooks. These workbooks allow the liquefaction triggering results (i.e., factors of safety and other depth dependent variables) from all three procedures to be readily compared at a given site. These workbooks will be provided free of charge to anyone interested in using them. Overall, for the sites analyzed herein, which have fairly high to very high peak ground accelerations, the three procedures agreed in predicting or not predicting liquefaction at many depths. For situations where the three procedures do not agree on liquefaction triggering, the author recommends using the prediction (i.e., "yes" or "no" liquefaction) agreed upon by two out of the three procedures.;In addition, a review of current relationships used to estimate the residual shear strengths of liquefied soil have been examined. Because site specific data influences the residual shear strength estimates, the author recommends comparing results from at least three different relationships in order to assign an estimated residual shear strength.;Soil liquefaction mitigation techniques have also been reviewed. In order to determine which of the mitigation techniques will work "best" all reasonable possibilities should be considered. Then, as soil properties and cost data become available some of the techniques will be disqualified, leaving only a few possible alternatives that can produce the desired outcome. |
