LIQUEFACTION MEASURE DEVICE OF STRUCTURE JUST UNDER GROUND AND CONSTRUCTION METHOD THEREFOR

PROBLEM TO BE SOLVED: To prevent liquefaction by inserting a drain pipe reaching a liquefaction anticipating layer of the just under ground from a vertical directional through hole formed in a footing of an existing structure. SOLUTION: A through hole reaching the under surface from the upper surface of a footing 2 is bored in a position for avoiding a footing pile 3 in the periphery of a bridge pier trunk part of the footing 2 of a structure 1. Next, a drain pipe 12 is driven into a liquefaction anticipating layer 4 of the just under ground 11 from the upper surface of the footing 2 with this through hole as a guide. Next, the drain pipe 12 becomes a drain, has water permeability capable of introducing water into the pipe by passing through a pipe body from the outside of the pipe, and is vertically extended over a thickness of the layer 4 so that the upper end of the pipe 12 is opened in the upper surface of the footing 2. Thus, pore water pressure energy at earthquake time can be absorbed by the drain pipe, and since pore water is discharged to the ground surface from the drain pipe, excessive pore water pressure can be dispersed, liquefaction of the footing just under ground can be restrained, workability can be improved, and a cost can be reduced.