Dilatancy based identification of liquefaction susceptibility

Abstract

This thesis focuses on liquefaction and dilatancy, both of which still remain as complex and controversial phenomena in geotechnical engineering. Even though the theoretical link between liquefaction susceptibility and dilatancy characteristics is known in geotechnical literature, quanti cation and practical de nition of this relationship could not be possible due to the di culties associated with the measurement of dilatancy angle. Thus, the main goal of this study is to develop a simple method which would allow the computation of liquefaction susceptibility based on the dilatancy of the soil. In this study, liquefaction initiation is achieved by cyclic loading which results in cyclic mobility of cohesionless soil samples, using constant-volume direct simple shear tests. Over 275 tests on 3 di erent sand types were conducted. The individual e ects of test characteristics; such as cyclic frequency, cyclic stress ratio and consolidation pressure on test results were investigated. Moreover, the e ect of average particle shape and size, both on dilatancy and liquefaction susceptibility was also investigated. Relationship between the peak dilation angle and number of loading cycles to liquefy were obtained from the results of direct simple shear tests and in order to link dilatancy to cyclic mobility, a novel empirical equation was used. This equation enabled the estimation of peak dilatancy from soil's relative density and mean e ective stress, using the data obtained from consolidated drained triaxial tests, conducted on the sand types under investigation.