A case of manual backfilling of a large sinkhole that occurred directly beneath a house foundation

Abstract

This report describes a case in which a large sinkhole (4.5m length, 3.0m width, and 1.2m depth) directly beneath a house foundation was manually backfilled by homeowner, who is non-experts without knowledge of geotechnical engineering or construction experience, using Mechanically Stabilized Crushed Stone M-30. The technical challenges in this case were ensuring permanent contact between the bottom of the house foundation and the backfilled crushed stone when backfilling and compaction were performed using low compaction energy, and ensuring the deformation rigidity of the backfilled crushed stone to support the house load. And construction challenge was that, since nonexperts were carrying out the work, the quality of the backfill crushed stone had to be guaranteed by the construction method regulations. By drawing up a construction plan for the backfilling work that utilized previous knowledge about soil compaction and by understanding the compression settlement characteristics of the backfilling crushed stone in advance, it was possible to create backfill ground with sufficient performance even when backfilled by non-experts. Even now, 10 months after backfilling was completed, no settlement has occurred.