The Ash Rd Carrier will be constructed in conjunction with the Amplification of Liverpool STP Stage 5A which will be project managed by United Group and will eventually connect to the existing Ash Rd Carrier Section 1.

The new Ash Rd carrier pipeline will be approximately 2.76 km in length and will be constructed beneath a densely occupied area of Prestons in Sydney’s west. As a result of strict community and environmental guidelines set for this project, the majority of the work will be constructed through the densely populated area utilising an Earth Pressure Balanced Boring Machine (EPBM) in order to combat the wet and soft nature of the ground along the pipeline route. The remaining section of the pipeline, which is in mostly unoccupied areas, will be constructed utilising conventional trenching techniques.

The nature of this project requires that the pipeline be constructed in long successive drives through the populated area, minimising the overall impact to residents. Rob Carr will construct this pipeline utilising an Iseki Microtunnel Boring Machine (MTBM) combined with an Iseki TCC600 and TCC700 Microtunnelling Drilling Heads.

Further works on this project will consist of the construction of 22 Maintenance Holes 17 Precast maintenance holes to be supplied by Humes and five in-Situ maintenance holes and ventilation system consisting of numerous induct and educt vents along the pipeline route. Furthermore, the pipe for the project will be supplied by I-Plex Pipelines who will supply both the trench pipe and microtunnelling pipe.

The day to day construction activity and project management for the Ash Rd Carrier pipeline will be conducted by Rob Carr. The company will also provide the necessary skilled staff and equipment to complete both the trenchless and trenching sections of the project. The company aims to further enforce their capability to provide a total project service to the client by taking on the entire pipeline construction works.

Cost effective and environmentally friendly

With the depth of the Ash Rd carrier pipeline ranging between 4 and 6.5 metres, the use of the microtunnelling process is necessitated as it provides a cost effective solution in constructing the more difficult parts of the pipeline. The small job footprint and closed faced slurry system that the Iseki Microtunnelling Machine provides will also aid the company in complying with the environmental requirements of the project. The most important thing to make note of when utilising the microtunnelling process is that it allows construction work to continue unobtrusively below the earth’s surface. Disruption to the immediate community and environment is kept to a minimum, allowing the public to continue with their day to day lives.

The word “microtunnelling” hardly seems to accurately depict the overall nature of work to be undertaken by Rob Carr on this project. The pipeline will be constructed utilising some heavy duty equipment, including 300T and 600T jacking frames and an Iseki TCC700 drilling head.

Microtunnelling systems

The “closed face slurry shield” method will be employed to construct the majority of the Ash Rd carrier in Prestons. With this method, microtunnelling commences when the drilling head is placed on the jacking frame. With the aid of various controls, the microtunnelling operator jacks forward the drilling head into the ground. The speed of the jacking and rotation of the cutters, steering, slurry fluid pressures and flow rates are all governed by the operator from inside the control room located above ground. Once the drilling head is fully inserted into the ground, the jacks are retracted and the first pipe is placed on the hydraulic jacking frame. Slurry lines and communications cables are then connected to the drilling head and microtunnelling again commences by advancing the drilling head and successively jacking the pipes forward.

The slurry spoil transport system provides earth pressure balance which is controlled by adjusting the flow rate from the control room. Consequently, the rate of spoil removal from the cutting face of the drilling head is removed in direct relation to rate of advancement of the drilling head. Furthermore, the slurry system balances groundwater pressure by adjusting the slurry pressure in the drilling head to equal the groundwater pressure. With this ability to vary the slurry cycle according to specific ground conditions, it allows microtunnelling to continue in wet or dry heavy clay and sandy soils without a decrease in performance. Commonly, Rob Carr utilises this system to install pipes of varying type and size in a variety of ground conditions. Pipe types include hobas, pvc, clay, steel and concrete, and pipe sizes vary between 300 mm and 1500 mm in diameter. Generally ground conditions have consisted of dry sand, saturated sand, alluvial soils, clay and rock.

The company also utilises a second microtunnelling system known as the Pilot Soil Displacement System. This involves a continuous line of hollow steel pilot rods being jacked into the ground from the entry shaft. Directional changes are made by the operator by turning the pilot rod line from the entry shaft. The direction of the line is commonly monitored using a theodolite or laser beam.

Upon the first pilot rod arriving in the exit pit, an auger system is then connected to the last pilot rod that was inserted. The carrier pipe of choice is then installed by the auger removing spoil. The pilot rods are then disconnected one by one in the exit shaft. Commonly this process is used for sizes up to and including 300 mm diameter pipes. However systems have been modified to allow for larger pipe insertion using this method.

The company

Established in 1989, Rob Carr has become a leading trenchless contractor focusing mainly on the construction of water, sewerage and drainage infrastructure. The company currently possesses a fleet of eight microtunnelling machines, which are utilised to successfully construct underground infrastructure in a variety of ground conditions. The company’s longevity and success has been primarily built on strong relationships with all clients.

Over the past few years, Rob Carr has worked for a diverse client group consisting of both government and private entities in all Australian States. Rob Carr has completed projects for clients such as Sydney Water, Brisbane Water, Brisbane City Council, Water Corporation WA, Toowoomba City Council, Melbourne Water and South East Water.

Rob Carr is quality assured through the Civil Contractors Federation for Safety, Quality and the Environment. Its project management capabilities and quality certified system allow the company to supply its clients with a total product from the early phases through to the completion of all construction work. The company prides itself in delivering safe and quality projects and strives to maintain its existing client base through a combination of high business ethics and value for money.