Case Studies
Sewer Failure
A new waterfront retaining wall was constructed at a seaside resort. The new retaining wall required to incorporate a sewer outfall near the base of the wall. The wall was constructed around the outfall but shortly after completion of backfilling behind the wall, the ground level was noticed to have sunk considerably immediately above the line of the sewer at the position of the outfall.
Cadogans was asked by the Client to provide an independent opinion as to the cause of the ground settlement. The issues addressed were as follows.
- Construction sequence and method statements
- Site records and photographs
- Design and detailing of wall and outfall
- Geotechnical profile at the location
- Site instructions and new construction detail
The issues were considered and analysed and the opinion given that the initial design was at fault, which had not addressed all of the requirements of movement and differential settlement between the wall and the sewer. The second, revised detail prepared by the original consultant and constructed by the contractor did take account of these issues.
