AQUIFER CUT-OFF METHOD FOR EXISTING WELL

PROBLEM TO BE SOLVED: To surely and efficiently prevent the incursion of ground water in an optional unnecessary aquifer of the existing well into the well. SOLUTION: A aquifer cut-off method of the existing well excavates a plurality of guide holes H2 up to a position near to a boundary B2 between the surface layer 1 and first aquifer 2 at equal intervals in the outside of a well pipe 10. Then, a shelf section 21 is formed in the bottom of an area corresponding to an unnecessary aquifer 2 in the outside of the well pipe 10 by grouting quick setting grout through the guide holes H2. Then, a wall section 30 is formed on the upper part of the shelf section 21 by grouting the grout through the guide holes H2. An impermeable layer is constituted of the shelf section 21 and wall section 30. Since the shelf section is subsequently piled up by the quick setting grout to make it impermeable, the incursion of ground water in the unnecessary aquifer 2 into the well can be prevented.