Navigating under the Nepean River
The construction of a pipeline under the Nepean River by horizontal directional drilling (HDD) from Woodriff Gardens in Penrith to Avoca Street in Emu Plains was the most critical, challenging and key task of the Emu Plains Primary Main Extension (EPPME) Project. The crossing involved installing 642 m of DN200 mm steel primary main pipe under the Great Western Highway at two locations and the Nepean River, which is adjacent to the highway.
An overground crossing had previously been constructed for the existing Secondary Pressure Pipeline. However, during the initial concept and design of the EPPME Project, developer Jemena decided that the Nepean River crossing should be installed underground, rather than as an overground structure or bridge crossing.
The pipeline was designed and constructed to be pigged by a reasonable range of commercially available, currently known, cleaning and in-line inspection pigs. All bends, whether field bends, fabricated bends or induction bends, had to have a minimum radius designed to permit the passage of pigs through the pipeline.Article continues below…
A rocky terrain
The HDD sites were located at Woodriff Gardens and Avoca Avenue Reserve in Penrith and Emu Plains respectively. Some re-design works of the HDD entry/exit locations and drill path were carried out by HDD contractor Codmah and Jemena after the initial design, due to restrictions imposed by the Roads and Maritime Authority for proposed future road works. Also taken into consideration were council and landowner imposed restrictions due to large mature trees in the park areas and the position of property boundaries along the drill path. The entry/exit point changes increased the length of the crossing by 79 m from the initial design length of 563 m, and introduced a horizontal direction change at the Woodriff Gardens end.
Prior to construction, the geotechnical report supplied by Jemena for the crossing indicated that there were significant layers of gravel, cobblestones and a likelihood of boulders at both proposed HDD sites. The ground conditions meant the crossing could not be constructed using traditional HDD techniques alone, because of the issues below.
Construction – The gravel, cobblestones and boulders were likely to be very unstable and would have repeatedly collapsed on the drill rods, drill head or hole-opener. This would have made maintaining the integrity of the hole impossible regardless of the drilling fluids used. It was extremely unlikely that a pipe could be pulled back through these ground conditions.
Environment - The gravel, cobblestones and boulders would make retaining and returning drilling fluids almost impossible. There was a high likelihood that there would be a loss of drilling fluids through these permeable ground conditions, which could result in frac outs.
To address these issues, Codmah decided on a strategy of installing a 600 mm steel case pipe from the surface down to the bed rock at both the entry and exit points of the crossing. The steel casing was installed down through the initial layer of silty clay/sand and through the layers of gravel, cobble, boulders and socket into the laminte (sandstone) layer.
Two methods were utilised for installing the steel casings – thrust boring and pipe ramming.
A launching pit was excavated at the entry site in Woodriff Gardens at an angle of approximately 13 degrees. This pit allowed the thrust boring equipment to be set-up and fixed into position at the required angle and location to install the casing. Installation commenced by boring the steel casing into the ground and auguring the material out through the casing. This method was very successful until the boulders, ranging from 300-400 mm, became too large to fit back through the casing pipe.
The boulders started to cause major problems with the case boring equipment, augers and casing pipe due to their size and strength. A decision was made to remove the 600 mm casing and increase the casing size to 700 mm diameter, which would allow additional room for removal through the casing. This was done to for a length of 36 m and a depth of approximately 9 m. At this point the boulders were too large, ranging from 450-500 mm, to continue and the second method of installation was employed.
The second method utilised pipe ramming technology, which has proved successful for Codmah when they previously used a Koloss Pipe Rammer and operator supplied by TT Asia Pacific in Brisbane. The rammer has 800 tonnes of thrust and is operated by a 900 cubic feet per minute (CFM) compressor. Due to the ground conditions, it was decided to use a 600 mm steel casing pipe with 12.7 mm wall thickness, and a heavy duty cutting head was welded on to the front end of the ramming pipe. The first three 12 m lengths were inserted into the previously cleaned out 700 mm casing, and each length was welded together as it was installed. Guide rails were fabricated to assist with supporting the pipe and rammer and these were specifically made to suit the thrust boring rails.
The ramming of the casing was very successful, and an installation rate of approximately 18 m a day was achieved. The welding of the joints proved to be the most time consuming operation, taking approximately four hours per weld. After the ramming into the bed rock was completed, the thrust boring machine was established again and the process of cleaning out the material from inside the casing began. This was done using a smaller diameter auger and rock head, which loosened up the material and then allowed removal through the casing.
Once cleaning had been completed, 2 cubic metres of grout was installed into the 600 mm casing pipe to form a seal between the bed rock and the casing. A 200 mm diameter steel casing with centralising legs was then installed into the 600 mm casing in order to provide support for the drill rods and maintain a central position at the work face for the drill bit.
Both sides of the crossing were completed using the same techniques prior to commencement of the HDD.
HDD pilot shot
Codmah engaged Highside Drilling Services to provide design, experience and guidance on the HDD method that would be used on the crossing. It was decided that due to the ground conditions and the casings at each end of the crossing, the HDD would have to be done using an intersect method.
This method involves the use of two HDD rigs, with pilot holes drilled from each end of the crossing that intersect at a point along the drill path.
The challenge for this intersect was the relative distance between the entry and exit points, which was much shorter than on a typical intersect. Combined with the fact the project would require drilling two horizontal curves, the window of opportunity for the intersect was much shorter than normal, at around 100 m. This would effectively allow for one approach, so it had to be right the first time.
In January 2012 Codmah’s Vermeer D100x120 rig and solids control GN500 gpm mud system was mobilised to the Woodriff Gardens site (Penrith side) and the equipment was set up. Highside Drilling Services, who provided all the equipment (Paratrack II) for guidance of the pilot shot and intersect, were established at the site and the HDD pilot hole commenced on 24 January 2012.
The guidance system was contained within two 4¾ inch non magnetic drill collars, which were threaded into the 4¾ inch Wenzel mud motor with a 6¼ inch PDC drill bit, and connected back to the site shed via wireline through the drill stems.
Approximately 500 m of pilot hole was completed by 8 February from the Penrith side and the crew then relocated to Avoca Avenue Reserve (Emu Plains side) where Codmah’s Vermeer D80x100 rig had been established. The pilot shot on this side commenced on 9 February with a duplicate set-up for drilling and guidance as per the Woodriff Gardens side.
Completing the intersection
The intersection of the two drill shots was completed on 23 February after approximately 350 m of the second pilot drill and within the first 50 m of straight drill path from the Emu Plains side. During this process it was necessary for both the D100 and D80 rigs to be in operation; the D80 rig drilled towards the already constructed pilot hole from the D100 rig. The D80 needed to be online and below the D100 pilot shot, and the axial magnets assisted with the positions of both heads once within a 5 m range of each other. As the D80 moved forward the D100 head retracted and eventually the D80 head broke through into the D100 pilot hole.
It was then necessary to guide the D100 drill head and drill stems into the new intersected D80 pilot hole by following the D80 drill head as it retracted back towards Emu Plains and the D100 pilot drill head came through the 200 mm centralising casing at the Emu Plains side on 25 February.
HDD hole opening and reaming
On completion of the pilot intersect, the guidance system, mud motors and drill head were removed, and the D80 rig and Highside Drilling left the site.
Preparations for reaming of the pilot hole commenced with the removal of the two 200 mm centralising casings from the 600 mm casing on each side. A ramming tool was used in reverse for this task.
Due to the location and ground conditions it was impossible to drill or lay a mud return line from one site to the other, and forward reaming was decided as the best approach. Codmah used a PDC reamer from Hard Metals in Sydney and this was installed into the drill stem string with 250 mm cutting wings at Woodriff Gardens in Penrith. Forward reaming commenced and as the reamer moved forward the second crew removed the drill stems from the string at Emu Plains and returned them back to the D100 at Woodriff Gardens.
Reaming and cleaning at 250 mm commenced on 1 March and was completed on 9 March. A second set of 312 mm wings was installed on to the reamer body and this commenced on 12 March and was completed on 20 March, including several cleaning runs.
Staging the pull back
The DN200 steel gas pipeline for the Nepean River crossing was supplied in 18 m lengths and coated in a dual fusion bonded epoxy (FBE) coating. Due to the length of the bore, at 642 m, it was impossible to string and weld the full bore length in one continuous length. To overcome this, during the reaming operations a small crew was utilised to string, weld, test and coat the HDD pipe. The pipe was strung and welded in three separate pipe strings of 220 m each. Upon completion of the strings the welds were subjected to 100 per cent x-ray NDT, blasted and a then had a Dirax HDD sleeve applied. Each pipe of the strings was subjected to full holiday detection, and any coating defects were repaired. The final test prior to pull back was a hydrostatic test on each string at 5,500 kPa to check for leaks.
Codmah procured a new 60 tonne pulling swivel and fabricated a pulling head from a 200 mm end cap, and the first pipe sling was lifted onto specially designed and fabricated pipe rollers. The pipe was then joined onto the pulling swivel and the first 36 m was installed into the 600 mm casing on Avoca Avenue in preparation for the main pull back.
Notification was given to the residents along Avoca Avenue prior to commencement and the pull back operation commenced on 21 March at 6 am. The installation rate on the pull back was averaged out at 28 m/s, and the first weld was ready at 8.30 am with the second and final weld ready at 1 pm. The pipeline was installed by 4.30 pm that day.
Jemena Asset Management undertook coating and cathodic protection tests in the following days and the HDD was tied into the main line on 30 March and hydrostatically tested on 13 April.
A greener installation
HDD was chosen over open-cut techniques to minimise potential environmental impacts and disruption to residents, businesses and road and water traffic.
During drilling, excess drill fluids and cuttings were put through the recycling units with great success and due to the use of forward reaming, the quantity of drill mud deposed of was dramatically reduced.
Sealing of the steel casings on both sides of the crossing at the intersection of the cobbles/boulders and bed rock was a major success and maintained good returns on both sides, preventing any frac outs or fluid losses.
Success and future outlook
The Nepean River Crossing was a great success and was the first HDD intersect in NSW.
There were numerous factors that contributed to the success of the project:
- Strong, co-operative and trusting relationship between Codmah and Jemena
- Management, planning and organisation of the works
- Codmah’s versatile and diversified equipment, workforce and management skills
- Appropriate and reliable equipment for the works
- Experienced, reliable and productive work crews
- Good relationship with Highside Drilling Pty Ltd and suppliers
- Innovation and problem solving capabilities.
Commissioning of the pipeline took place on 19 and 20 April, and final restoration and disestablishment works were completed the following week.
Codmah would like to use this crossing as a platform to build the company’s larger HDD capabilities and have acquired a Vermeer D80x100 rig to go with the D100x120 rig. The company hopes to develop this area of the business further and take its experience from this project to provide improved engineering, design and installation solutions for trenchless utility installation projects.