The uplift of underground structures in liquefiable soil due to earthquake induced liquefaction may lead to severe damage.The use of cutoff walls is believed to be an effective approach in diminishing the uplift

but its mechanism is still not clear

and the design parameters of the cutoff walls also deserve investigation.Effective stress based dynamic finite element method was used in the efforts to clarify the mechanism as well as the influences of different design parameters of the cutoff walls.It was found that cutoff walls could reduce the liquefaction-induced uplift of underground structures to considerable amount.After looking into the excess pore pressure

soil deformation

stress path as well as stress-strain relationship

the effects of the cutoff walls were identified as reducing the deformation and flow of the liquefiable soil.Although the cutoff walls could decrease the excess pore pressure at small earthquake excitation;but during large earthquake

the excess pore pressure was larger for the cases with cutoff walls.The reasons were identified and explained.The important design parameters including the location

embedment length into the non-liquefied soil

and the lapping length with the underground structure

were investigated.In order to be effective

the cutoff walls must be located as closely as possible to the underground structure;they also need to be embedded in the non-liquefied soil with sufficient length;and their stiffness must be higher enough.