Perforator® auger system aids motorway crossings project

Oct 06, 2010

Anyone driving around the UK at the moment using the motorway system will have noticed that there is a lot of work underway to install a huge automated traffic management system and information sign network. Part of this operation, organised by client The Highways Agency and its consulting engineer A.One+, one project has recently been underway on the M56 motorway between Junctions 9 and 16 under the ‘Triple Package Advanced Works’ designation.

After careful consideration of the options available for the construction of the fibre optic cabling system required for the management network beneath this busy section of the motorway, it was decided to use horizontal directional drilling techniques for the majority of the crossing installations. Ground investigations, which were undertaken using bore holes at each crossing location and on both sides of the motorway showed that this was a very suitable trenchless technique for the conditions.

The main contractor appointed to complete the project was A E Yates Ltd, with its sister company, A E Yates Trenchless Solutions Ltd, being awarded the trenchless installation works.
The majority of the crossings, some 25 out of 26, were completed using various HDD drilling rigs as per the project plan. The HDD bores varied in length between 40 and 100 m and comprised the installation of 4-way 110 mm diameter conduit pipes. However, at one particular crossing location near Helsby, the work site was very restricted in space, both on the launch and reception sides of the motorway, which meant that the use of the HDD technique was not possible, so another installation option had to be found.
Investigation of the options available led engineers at A E Yates to select the pilot auger microtunnelling technique for the limited-space site.
With the auger crossing site comprising ground conditions of very compact sand and weathered sandstone, the correct choice of installation technique was vital, whilst still being able to operate in the confined spaces on either side of the motorway.
Again careful consideration of the options available led to the choice of a Perforator PB85V pilot auger microtunnelling system as the best choice system for the situation in hand.
The auger crossing comprised the installation of a 45 m long, 300 mm diameter ‘lost steel tube’ which was to act as a carrier pipe for four 110 mm diameter purple PE80 MDPE conduit pipes, manufactured to DIN 8074/8075 specification and supplied by Drain Centre of Wigan, into which the fibre optic cables of the traffic management system would be installed.
The basic PBA85 pilot boring system is a compact, multi-purpose thrust boring machine designed for pipe line, house connection and steel pipe jacking installations of up to 610 mm o.d., as is the PBA85V. The machine is used in combination with re-usable or lost steel casings. The machine bed and additional extension frames allow the use of casings up to 6 m long. Soils are mechanically removed towards the working pit by a rotating string of augers and cutter heads can be replaced when soil conditions change. PBA 85 machines can be equipped with a navigation system and pilot rods in order to keep tolerances required for house and main sewer connections of between DN150 to DN500. Directional control and surveying is achieved using a monitor, an optic system with CCD camera and a diode target plate.

However, for the M56 crossing project the contractor chose the PBA85V unit because the one very specific difference between the standard PBA85 rig and the PBA85V system is that, on the ‘V’ version, a gearbox normally used in the Perforator® PBA150 rig is fitted. This allows the ‘V’ unit to boast double the torque capacity of the basic unit. This would enable the bore to be completed efficiently in the harder ground conditions of the crossing site under the M56.

To complete the crossing first the rig is established in the start shaft on the line and level required for the crossing. As the pilot bore progresses the use of the Optic Electronic Navigation System (OEN), which is a laser based system, enables the pilot bore to be driven along the required route of the bore towards the target point.
Once the pilot bore is completed the cutting head is changed to an auger system which enlarges the pilot hole, removing the spoil created via the auger chain that is installed behind the auger cutting head.
With the bore at the correct size the pipe installation can then be completed by jacking the necessary pipe into place behind the auger chain whilst removing the displaced auger units at the reception shaft.
The PBA85V can also be utilised as an HDD rig where circumstances warrant and allow with a directional drilling system which can be fitted to the system which utilises the twin wall pilot rods of the standard PBA 85 system which are designed to accept high pressure HDD fluids, to create the initial bore. Subsequently, the high pressure drilling fluids are delivered to special rotary reamers using a purpose built pump, tank and mixer unit with a 2,000 litre capacity. Towing attachments and swivels have been specially designed to work within the PBA85V’s 65 tonnes of pullback capacity to enable the pull-in of the product pipe.
Installations on the M56 project as a whole, including the HDD works, started in January 2010 and were completed by March 2010. The HDD installations took an average of two restricted-hours night shifts each to complete. These were carried out in this manner because of traffic management constraints, restricted working space, and a requirement to dig the HDD rigs in at each site as each set-up was working adjacent to or under the live and open M56 motorway. Works on the auger crossing installation took 5 day shifts subsequent to shaft construction and site preparation.
According to Graham Smedley, managing director of Perforator® Ltd: "Using Perforator’s PBA guided boring systems on this auger crossing enabled the completion of what might otherwise have been a difficult installation to complete given the restrictions on the site in terms of both working close to an operational motorway and in the limited space available. We were very pleased to be able to provide a solution that proved so effective for the contractor. The PBA85V, and other members of the PBA family of pilot auger systems, enables the installation of pipes in straight-lines to grade in a wide variety of situations. Because of the system’s accuracy, installation of other utility pipe networks such as gas mains, water mains and drainage pipelines can also be achieved in areas surrounded by other services and known obstacles."
Commenting on the project for A E Yates site manager Sven Till said: "A difficult challenge was successfully undertaken by AEY Trenchless Solutions, in providing a solution to a problem for the Highways Agency by the use of the Perforator machine. A job well done"
>> This article is presented with permission of Trenchless Works / NoDig Media Services. <<

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