The Sang Dam is a vital earth dam structure that was affected by land movement and was underlain by an active fault. The dam is one of Gisborne's main catchments and is reasonably isolated, and the steep terrain in some areas made access difficult. 

A geotechnical investigation of the site and design of remedial works to stabilize the dam and avoid downstream implications were required. LDE was contracted to undertake the work as soon as possible to restore the reservoir capacity and enable refilling. It would have significant impacts if this were not achieved, or if a failure occurred. 

The geotechnical investigation determined the geometry and strength of the materials forming the dam. Samples were then laboratory tested to inform geotechnical design parameters and fill compaction specifications. Results were used for optimizing fill strength and monitoring compaction during construction. The geotechnical team on this worked directly with the civil engineers to analyze and design remedial works.

Civil scope included slope stability analysis and construction drawings using the information and recommendations from the geotechnical investigation while following NZSOLD guidelines. This also comprised a design of the filtered under-drainage system, preparation of construction specifications, and schedules of quantities and prices. The mitigation design of the dam was to prevent complete failure, downstream flooding and the loss of water supply.

Given the structure's significance, cost, and importance of properly constructed underfill (including correctly compacted fill), LDE also carried out construction supervision.

Location: Waingaki, Gisborne
Client: Gisborne District Council