EVALUATION OF THE IN-SITU STATE OF FRASER-RIVER SAND

Liquefaction flow slides are recurrent phenomena in the Fraser River d elta near Sand Heads. The reasons for these failures an unexplained an d remained speculative. An investigation of a liquefaction flow slide that occurred in 1985 in the Fraser River near Sand Heads has been und ertaken using steady state concepts. For liquefaction flow slides to o ccur in sand deposits, the sand must strain soften in undrained shear and the in situ shear stresses must be greater than the available undr ained shear strength. Laboratory tests have been performed on reconsti tuted Fraser River sand samples to establish steady state parameters. Moist tamping methods and water pluviation techniques were used for pr eparing soil samples in the laboratory. Shear wave velocity measuremen ts were used to evaluate the in situ state of the young, uncemented sa nd deposits. The in situ state of the young sand deposits near Sand He ads was found to be on the loose side of steady state, consistent with the field observation of instability.