CONSTRUCTION METHOD FOR STRUCTURE FOR PASSING WATER UNDER FLOORBOARD AND UNDERGROUND STRUCTURE

PROBLEM TO BE SOLVED: To provide a construction method for a structure for passing water under a floorboard, and an underground structure causing no cutoff of a flow of underground water. SOLUTION: This underground structure is constructed in a state of adjacently arranging an underground water permeating block for passing water under the floorboard and an underground water cutoff block for checking the passing of water under the floorboard. A boundary of both blocks is partitioned by at least a partition wall removable in an upper part. A box body is manufactured in the drained underground water cutoff block. The box body is moved to the underground water permeating block from the underground water cutoff block by using buoyancy, and the box body is arranged on a bottom surface of the underground water permeating block.