Kambalda DN375 Sewer Replacement and Associated Works

February 2020

The Kambalda West sewer network was constructed by Western Mining Corporation in the 1970’s. The sewer main was constructed with asbestos cement (AC) pipe but the 150m replacement section, which is to be constructed in a floodway is above ground and to be constructed from GRP pipe. Additional works for this project are replacement of two dilapidated stormwater culverts and the upgrade of the existing access track.

We have now completed the second swing for the works following the Christmas shutdown with practical completion carried out on 28 January. We will spend a third part swing beyond this to complete miscellaneous works additional to the original scope.

The project required the fabrication of a stainless steel sluice gate (penstock) and weir upstream of the works. The penstock design drawing supplied had insufficient detail to fabricate the unit without making several assumptions. DM Civil designed and detailed this unit in-house in order to provide enough detail for our supplier to produce a workable unit. The shop drawing was produced by our in-house draftsman. The access chamber has a bifurcation to both the treatment works as well as to an emergency overflow pond.

Another issue that required special attention was the connections between the existing AC pipe, the existing PVC pipe and the new GRP pipe. Custom made level invert tapers were required in the correct size to allow for ductile iron connectors to be used at these interfaces. Our engineering manager, Bruce Shaw, was consulted by the project team to provide his experience and expertise in this area. Bruce’s previous experience as a pipeline and pump designer at Hardie Pipelines gave us exactly the advice needed for this task. His wealth of knowledge avoided costly mistakes being made with pipes produced so long ago that have some characteristics unknown to modern designers and field staff.

The design of the GRP pipe required the procurement of 12m lengths to maintain stiffness for the above ground section, which is supported on steel pipe cradles. It was through the purchasing department that we were able to call upon a long time supplier to provide a special run of this non-standard length to be ready on time and to keep on schedule.

No regional project can be completed without thorough planning for materials delivery. Plans and orders of all materials were through our purchasing department. Almost all machinery and materials were conveyed by our own trucks through the transport and logistics department. Our team made several trips back and forth to ensure that deliveries were made reliably, on time and using our own resources.

An essential part of working in regional areas is to satisfy the requirements of the local operators. The region is based at the wastewater treatment works, only a few hundred metres downstream of the works. This allowed our crew to liaise directly with the local staff to fine-tune the installation of components such as the penstock. This was installed upstream of the works into an existing access chamber. After on-site discussions between DM Civil and the local operator, we received a request from head office to install a second penstock to enable isolation of both channels in the bifurcated access chamber.

The existing asbestos cement (AC) pipework was in a dilapidated state and except for the above section being replaced by DM Civil, this pipework had been relined with a spiral wound plastic. Despite this refurbishment, care was needed working around the pipe to avoid breaking away fragments or puncturing the plastic lining. The scope of works originally required the placement of fill material over the existing AC pipe to a minimum cover followed by compaction. DM Civil clarified that we made no allowance for this compaction because of the risk of pipe failure. As a departure from the scope, we have placed fill material around and over the pipe and coated this with ballast material to guard against soil erosion from wind and rain.

The project has been a great success and a credit to the construction crew and our office based support. The client has thanked us for producing an upgraded asset delivered on time and under budget with little requirement for direction or management throughout. DM Civil’s adaptive in-house capabilities, diverse long-standing experience and hands on approach ensured project delivery and highlighted our ability to provide tailored, sustainable civil contracting solutions to regional Australia.