Early in 2013 Unitywater awarded a contract for the HDD crossing of the Maroochy River in Queensland to Coe Drilling. The crossing forms part of the Suncoast sewage treatment plant closure and transfer pumping station and rising main upgrade works.
The Maroochy River HDD crossing involved the construction of a sewer rising main under the Maroochy River. This forms part of the link between the Suncoast Treatment Plant (which is scheduled for closure in mid-2014) and the Finland Road Treatment Plant. Once completed sewerage will be pumped from the Suncoast Treatment Plant site via a new pump station and 6 km of rising main to the Finland Road site.
THE PROJECT
The project included the design, procurement and construction of 820 m of DN500 HDPE 100 sewage rising main.
Given the project location and the surrounding geology, a detailed design was required to satisfy the client’s specifications and alleviate concerns regarding the risk of hydrofracture in the Maroochy River.
The alignment chosen by Coe Drilling placed the crossing in the soft alluvial soils under the Maroochy River. By placing the crossing in this softer material Coe Drilling was able to deliver a cost-effective solution to meet the client’s requirements. The consequence of placing the crossing in this formation was an increase in the risk of hydrofracture. Coe Drilling was able to demonstrate that this risk could be managed by completing a detailed hydrofracture analysis of the theoretical profile.
HDD OPERATIONS
Drilling commenced early in August 2013 following finalisation and peer review of all design documentation.
Using Coe Drilling’s Prime PD500 drill rig, a pilot hole was drilled from the southern side of the Maroochy River, near the Maroochy Mulitsports Complex. Throughout this phase of construction, down hole pressures were continually monitored, using a down hole pressure probe, to ensure that no hydrofracture occurred.
The twelve-and-a-quarter inch pilot hole was successfully completed without incident in mid-August 2013.
Following the successful completion of the pilot hole two reaming passes and a hole conditioning pass were completed prior to pipe installation occurring.
The product pipe was fabricated using industry standard practises on the northern side of the river. Product pipe installation was successfully completed mid-September 2013.