SITE INVESTIGATIONS TO EVALUATE FLOW LIQUEFACTION SLIDES AT SAND HEADS, FRASER-RIVER DELTA

Spontaneous flow liquefaction is a recurrent process in the progradati on of the Fraser River delta. A portion of the Fraser River delta was investigated by seismic and resistivity cone penetration testing, by t he spectral analysis of surface waves method and by soil and vapour sa mpling in an effort to determine site stratigraphy, in situ state, and degree of saturation to explore the enigma of spontaneous now liquefa ction. A pore pressure and till sensor package was installed as part o f the investigation, to monitor tidal drawdown effects. Results indica ted that the seabed at shallow depth was partially saturated, containi ng a significant volume of methane gas, which affected the dynamic por e pressure response during tidal drawdown. A reduction in effective st ress of up to 16.5 kPa was measured, along with a time lag between tid al drawdown and pore pressure response of 50 min, This suggests that g as-damping effects are a significant factor in initiating spontaneous liquefaction of loose unaged sands where they rest on submarine slopes . The in situ test results showed that newly deposited Fraser River sa nds possess a high susceptibility to flow liquefaction.