IMPERMEABLE WORK METHOD FOR UNDERGROUND STRUCTURE BY IMPERMEABLE WALL AND SLIGHTLY PERMEABLE BOTTOM BASE

摘要

PROBLEM TO BE SOLVED: To secure dry work and prevent floating of an underground structure by creating a lower slightly permeable bottom base at a particular lower position from the upper slightly permeable bottom base created at the deeper position from the underground structure. SOLUTION: A grid-shaped beam 2c for connecting inner and outer impermeable walls 2a, 2b in the ground consisting of sand gravel layer with a high permeability and a shallow groundwater level is built, thereafter, the impermeable walls 2a, 2b are built. Then, an upper slightly permeable bottom base 1a is built at a position deeper than the underground structure B, a lower slightly permeable bottom base 1b having a plan shape larger than that of the upper slightly permeable bottom base 1a is creased at a position lower by layer thickness of a drain layer from the upper slightly permeable bottom base 1a. Then, for each closed portion surrounded by the inner and outer impermeable walls 2a, 2b and grid-shaped beam 2c, the groundwater level is lowered by a water pumping-up well 4 provided to a depth reaching a water drain layer A", thereafter, the ground surrounded by the upper slightly permeable bottom base 1a and the inner impermeable wall 2a is excavated and the underground structure B is constructed.