Undrained Response of Sand Containing Non-Plastic Fines

Current simplified procedures for estimating liquefaction resistance consider an increase in the measured SPT-N for sand containing fines. Nevertheless, it is not clear if this increase corresponds to an increase in resistance or to a decrease in penetration resistance due to fines compressibility. To date, several researchers have studied in laboratory the influence of non-plastic fines on the liquefaction resistance of sands considering different approaches in which they keep constant a density index for comparison such as void ratio, relative density, sand-skeleton void ratio or inter-granular void ratio, equivalent void ratio and inter-fine void ratio. This has led to divergent conclusions that will be described and explained in this paper. The interest in this topic has increased after the recent events of liquefaction in Taiwan, New Zealand or Tokyo, where liquefaction caused significant damage to buildings, houses, retaining structures and underground infrastructure. Sand retrieved from Tokyo Bay was studied in this research. A hollow cylindrical torsional shear apparatus was used to conduct a series of tests to determine the effect of non-plastic fines on the liquefaction potential of sand. Given the disagreement of the role of non-plastic fines in previous researches, it was decided to test samples at the same SPT N-value. The coefficient of volume compressibility, mv, was selected for comparison as it is inversely related to the SPT N-value. Samples were consolidated at the same mvvalue and then sheared under monotonic and cyclic loading. Later, the volumetric strain after liquefaction was also measured and results are presented herein and discussed. Relevant conclusions regarding the role of non-plastic fines on the undrained behavior of sands, are provided.