The value of AJ Lucas’ HDD technology and pre-engineering drill on paper workshops was once again highlighted with the construction of the Three Towns, as part of the NSW Government’s Priority Sewerage Program.
The $A118 million ‘Three Towns’ sewerage scheme will connect residents and businesses in Glossodia, Freemans Reach and Wilberforce with a reticulated sewerage system, northwest of Sydney. The project involves constructing over
116 kilometres of pipeline, including a
760 metre horizontal directional drill under the Hawkesbury River.Article continues below…
The scheme will provide improved sewerage services to the unsewered urban areas of the three towns through the installation of a pressure sewerage system and associated infrastructure. Wastewater from the three towns will be transferred directly to Richmond Sewage Treatment Plant.
By connecting to the new system residents will be helping to reduce the number of septic systems in the area. This will improve local waterways and reduce risks to public health.
One of the challenges of the 760 metre drill was a layer of large cobbles almost ten metres thick at both entry and exit locations. A detailed drilling management plan was required, whereby large diameter heavy walled casings were hammered down through the cobble layer on both sides. The cobbles were removed from the inside of the casing using an auger system prior to the commencement of drilling operations commencing.
One of the difficulties with this operation is maintaining angle and direction of the casing during the installation. Lucas engineers have performed this operation many times in the past and have established a methodology which allows the casing to be installed with a high degree of accuracy.
Cobbles present a huge problem for any HDD operation as they:
- Do not allow a competent hole to be drilled.
- Do not allow drilling fluid to be returned up the hole.
- Are large and heavy and cannot be removed from the borehole using drilling fluid.
- Collapse around the drilling tooling causing stuck pipe.
Additionally, due to limited pipe stringing areas, drilling operations and pipe stringing were completed from the one side, requiring the drilling spread to be completely de-rigged and re-mobilised to the exit side for pipe installation.
Despite the complications, Lucas completed the project on target at a cost slightly less than the anticipated Target Cost Estimate (TCE) which was established in conjunction with the alliance partners. The use of AJ Lucas’ HDD capabilities resulted in the least environmental impact of all nominated options, and provided a viable solution to an otherwise marginal HDD project.