Avaliação da resistência à liquefacção

Guidelines for Evaluating Liquefaction Resistance Using Shear Wave Velocity Measurements and Simplified Procedures.

Predicting the liquefaction resistance of soil is an important step in the engineering design of new and the retrofit of existing structures in earthquake-prone regions. The procedure currently used in the U.S. and throughout much of the world to predict liquefaction resistance is termed the simplified procedure. This simplified procedure was originally developed by H. B. Seed and I. M. Idriss in the late 1960s using blow count from the Standard Penetration Test. Small-strain, shear wave velocity measurements provide a promising alternative and/or supplement to the penetration-based approach. This report presents draft guidelines for evaluating liquefaction resistance using shear wave velocity measurements. These draft guidelines were written in cooperation with industry, researchers and practitioners, and evolved from workshops in 1996 and 1998. The guidelines outline the development of a recommended procedure, which follows the general format of the penetration-based simplified procedure. The proposed procedure has been validated through case history data from more than 20 earthquakes and 70 measurement sites in soils ranging from clean fine sand to sandy gravel with cobbles to profiles including silty clay layers. Liquefaction resistance curves were established by applying a modified relationship between shear wave velocity and cyclic stress ratio for constant average cyclic shear strain suggested by R. Dobry. These curves correctly predict moderate to high liquefaction potential for over 95% of the liquefaction case histories, and are shown to be consistent with the penetration-based curves. To further validate the procedure, additional case histories are needed with all soil types that have and have not liquefied, particularly from deeper deposits (depth > 8 m) and from denser soils (shear wave velocity > 200 m/s) shaken by stronger ground motions (peak ground acceleration > 0.4 g). The guidelines serve as a resource document for a final recommended practice, and for practitioners and researchers involved in evaluating soil liquefaction resistance.