Somme Parade retaining wall - update

The issue

During post-construction monitoring by the Whanganui Alliance, it was discovered there had been some movement in a short section of the retaining wall, immediately next to a stormwater outlet (the extent of the movement is within the wall design tolerances determined by the design engineers).

Investigations showed that several pipe sections of the main had separated, resulting in stormwater discharging into the ground. The Alliance mobilised quickly to undertake further geotechnical testing of the area around the pipeline and area of wall movement.

This work is outside the control of the contractor and was unforeseen when the designs for the drop-out repairs were established.

Test results

Initial results of the testing involved constructing a test anchor to provide details of an anchor design to ensure there is no further movement within the area. The test anchor has now been tested with good results. The design engineers have determined the number and location of anchors.

What is being done

The installation of anchors has begun. The work is expected to take around a month to complete.

Following the installation of anchors the Alliance will undertake repairs to the stormwater pipeline. The stormwater pipe repairs will require a full road closure. During this time (approx. three weeks) the Seddon Street detour route will be used for traffic.

Fencing and site reinstatement will be completed following the anchor and stormwater works. All works are expected to be completed by September.

Funding

Funding is currently at an advance Funding Assistance Rate (FAR) rate of 80% from Waka Kotahi NZ Transport Agency. This level of funding will revert to a standard FAR (62%) on 1 July 2024.

• The Whanganui Alliance is a joint collaboration between Downer and the council for the district’s roading infrastructure.