UPLIFT BEHAVIOR OF UNDERGROUND STRUCTURES CAUSED BY LIQUEFACTION OF SURROUNDING SOIL DURING EARTHQUAKE

抄録

During past earthquakes, several types of underground structure were damaged by uplift movement, because they were relatively light compared with the buoyancy force resulting from liquefaction of the adjacent subsoil by earthquake. To investigate this uplift behavior, a variety of model tests were conducted. In these tests, the uplift of underground structures was caused by both nearly instantaneous deformation of a surrounding subsoil layer and gradual movement of a pore fluid, while reconsolidation of liquefied soil resulted in settlement of the structure. Several different effects of structure type on uplift behavior were observed, including reduction of excess pore water pressure in a soil layer overlying completely-buried box structures and three dimensional deformation of the backfill soil surrounding a manhole together with deformation of original soils thus "squeezing" the backfill soil into the space occupied by the manhole. Analysis of the test results suggests that a safety factor against uplift, which was defined based on the equilibrium of vertical force acting on the structure, can be used to evaluate the triggering of uplift.