Mount Street Trunk Water Main Replacement

March 2019

We have now reached a milestone in the Mount Street contract for Water Corporation.

Our scope of works includes the replacement of a segment of the main water feed into the Perth central business district. This element being the DN900 steel water main that was laid in the northern road pavement lane from the lower end centre island up the hill and into Kings Park land. The scope of works also included the replacement of the reticulation mains which ran on both sides of the dual lanes in the verge.

The new configuration feeds all buildings on both sides of the road from a single DN375 PVC main, also laid in the northern road pavement lane parallel to the DN900, but at a shallower level. The new design of the reticulation to the buildings is similar to our recent cast iron replacement schemes where we charged the new main after a short shutdown and proceed to change over services individually with very short shutdowns to the individual properties.

In keeping with our originally proposed methodology, we now have an operating reticulation system that will be kept in service for the duration of the remaining works, except for a shutdown during the DN900 main connection. This sequencing of the works is designed to mitigate the risk of a water outage to the local residents and businesses and was an important innovation in our original tender submission.

The initial challenge for DM Civil was the negotiations with City of Perth to reach agreement on the pruning of the boulevard trees planted on the verge and centre island. These were Queensland Box (Lophostemon confertus) and Jacaranda (Jacaranda mimisifolia) trees, essential to the amenity of the area. After extensive consultation with registered arborists, the City of Perth’s term contractor was used to appropriately prune the overarching trees in accordance with approved procedures and to the satisfaction of City of Perth. There were 70 trees to be considered. The result is an enhanced grove of trees in keeping with the most photographed area of Perth City.

Reinstatement of the road pavement was required for the full width of the Mount Street northern carriageway. Compaction and levelling on the steep grade was a difficult task. However, the standards were achieved and the finished product has proven to match and exceed the original pavement.

An excellent example of value adding for the contract was the decision by DM Civil to construct the DN900 distribution main using trenchless techniques under the traffic roundabout at Cliff Street and existing vegetation located within the Kings Park grounds. This was carried out by the trenchless division and provided at no additional cost to the client. The benefit to Water Corporation, Botanical Parks and Gardens Authority, the local residents and the public including tourists, was a continuous traffic flow and retention of high value trees in our world class park.

One of the tender requirements was to demonstrate a record of stakeholder management in high density and politically sensitive environments. DM Civil has a good reputation in this area and this was certainly relevant to being chosen to bid on the project. To date, the project has not received any adverse press or on-site complaints. In fact, we have received positive feedback throughout the project process.

Due to the original delay in the award of contract and possession of site, the construction programme was pushed into the summer period. The security of critical water supply to the CBD during the summer months required the postponing of the tie-in process for the DN900 main. This is now scheduled for the autumn months where demand will be reduced to the point where contingency supplies can be back-fed from the network.

Discover how our multi-disciplined capabilities enabled us to deliver this complex scope of work.