Unique relation between pore water pressure generated at the first loading cycle and liquefaction resistance

Abstract

Accurate evaluation of excess pore water pressure (EPWP) generated in earthquake vibration is a key important factor in seismic engineering against liquefaction. Most previous studies were focused on the relation between cyclic resistance and EPWP developed in the entire liquefaction process. Only a few researchers pointed out that the maximum EPWP ratio accumulated at the first loading cycle, represented by (Δu/p0)max−N1, was intimately related to the liquefaction resistance of sand. Based on this viewpoint, liquefaction resistance of sandy soils can be improved significantly by repressing EPWP at the first cycle by engineering countermeasures. The relationship between (Δu/p0)max−N1 and liquefaction resistance or the cyclic number to liquefaction Nf, however, has not been established quantitatively yet. Moreover, whether this relationship is influenced by stress states such as liquefaction-induced anisotropy, structure or fabric of soils, and loading conditions, is not clear yet. Therefore, a series of undrained cyclic triaxial loading tests were conducted on Toyoura sand, a clean sand famous in Japan, to identify the above-mentioned uncertainties. Based on the test results, a unique empirical (Δu/p0)max−N1-Nf relation was proposed to evaluate the liquefaction resistance. Finally, three typical samples were given to display the application of (Δu/p0)max−N1-Nf relation.