METHOD FOR IMPROVING GROUND UNDER EXISTING STRUCTURE

To provide a method for improving the ground under an existing structure, which can improve the ground while preventing both leakage of sewage, etc. inside the existing structure into the ground, and infiltration of groundwater into the existing structure.SOLUTION: A ground improvement method for improving the ground G1 below an existing structure C installed in a water area comprises an upper slab penetration step of penetrating a first penetration rod R1 into an upper slab S1, an upper slab drilling step of forming a first through hole H1 in the upper slab S1 with a first drilling rod R2, a middle slab penetration step in which the first drilling rod R2 is used as a second penetration rod and the second penetration rod R2 is penetrated into the middle slab S2, a middle slab drilling step in which a second through hole H1 is formed in the middle slab S2 using a third drilling rod R3, a lower slab penetration step in which the third drilling rod R3 is used as a third penetration rod and the third penetration rod R3 is penetrated into the lower slab S3, a lower slab drilling step of forming a third through hole H3 in the lower slab S3 with the third drilling rod R4, and a ground improvement step for improving ground G1 with an improvement rod Ra.SELECTED DRAWING: Figure 14 【課題】既設構造物内にある下水等の地盤内への漏洩と、地下水の既設構造物内への浸入の双方を防止しながら地盤改良を行うことのできる、既設構造物下の地盤改良方法を提供する。【解決手段】水域に設けられている既設構造物Ｃの下方地盤Ｇ１を改良する地盤改良方法であり、上床版Ｓ１に第１貫入ロッドＲ１を貫入させる上床版貫入工程、第１削孔ロッドＲ２にて上床版Ｓ１に第１貫通孔Ｈ１を形成する上床版貫通工程、第１削孔ロッドＲ２を第２貫入ロッドとして、中床版Ｓ２に第２貫入ロッドＲ２を貫入させる中床版貫入工程、第３削孔ロッドＲ３にて中床版Ｓ２に第２貫通孔Ｈ１を形成する中床版貫通工程、第３削孔ロッドＲ３を第３貫入ロッドとして下床版Ｓ３に第３貫入ロッドＲ３を貫入させる下床版貫入工程、第３削孔ロッドＲ４にて下床版Ｓ３に第３貫通孔Ｈ３を形成する下床版貫通工程、改良ロッドＲａにて地盤Ｇ１に地盤改良を行う地盤改良工程とを有する。【選択図】図１４