The variation of the gross pressure of backfill soil before and after liquefaction behind a retaining structure was analyzed.The pore water pressure becomes higher after the backfill soil behind a retaining structure is liquefied

while the effective stress decreases.Also

the earth pressure is disappearing while the soil particles are suspended.Due to that groundwater has characteristics of viscous fluid

the earth pressure acting on the retaining wall equals to the force isotropically that is applied by the viscous fluid with a saturated gravity ofγsat.So the gross pressure of the backfill soil on the retaining structure increases evidently in the post liquefaction stage.More attention should be paid in this stage.Results indicate that the gross soil pressure before and after liquefaction reduce as the underground water level moves down

but the ratio of the gross pressure presents the trends which first increase then decrease.With the increase of the pressure coefficient K0

the gross pressure increases gradually（In the case of entirely emerged in water

the pressure coefficient will be stable）.Since the gross pressure before liquefaction increases faster

the pressure ratio becomes smaller as the pressure coefficient increases.