Specialist trenchless contractor, Trenchless Solutions Ltd (TSL) recently undertook two grade-critical guided auger bore installations as a specialist subcontractor for client United Utilities (UU) as part of the Blackburn UID works, Audley Range and Queens Park Road project. The works and the engineering planning were carried out by UU with J.K Guest Group being appointed as the main contractor for the project.
Investigations of the ground conditions prior to planning of the project showed that, at the level of the pipe installation, conditions consisted of soft to stiff clay, which was ideal for the guided auger boring technique chosen for works. As well as being well-suited to the prevailing ground conditions, the method also meant that the gravity sewer being installed could be accurately aligned on both line and grade, the latter being critical to the success of the installations.
The two bores required to complete the project comprised one pipeline of 57 m in length and another of 60 m in length at depths of about 4 to 4.5 m, respectively. Both of the pipes were installed using DN700 GRP Hobas jacking pipe.
The start date was Aug. 16, 2011, with a finish date Sept. 16, 2011. Both the guided auger installations were completed in just 20 working days, including setup at both launch pits and the move between launch sites. All the necessary start and reception shafts were installed ahead of the Auger Boring works by the main contractor JK Guest.
Directional control of the pilot bore of the three stage installation is achieved using a monitored optic system using a CCD camera and a diode target plate. Once the pilot bore is completed, the second stage is enlargement of the pilot bore with an auger and casings which uses the initial pilot route as a guide. After enlargement of the pilot to the desired size, the product pipe is jacked into position behind the auger casings with these casing being recovered at the reception pit of the installation. An animation of the technique used at Blackburn can be viewed on the TSL website using the link: http://www.trenchlesssolutions.co.uk/services/guided-auger-boring/
In this instance, the DN700 GRP jacking pipe was supplied direct by HOBAS in 3-m lengths, with push-fit joints designed for pipe jacking applications.
In the event all participating parties from client through contractor and sub contractor were very pleased with the ultimate result of each of the bores given that both holed on precisely on target in terms of line with the 60-m drive holing just 3 mm low of the target and the 57-m drive holing just 8 mm low.
Commenting on the project for the client, Mike Purcell, construction manager said, “The two drives were undertaken safely and professionally without incident. Both drives were well within the tolerances we required.”
Main contractor for the project, JK GUEST Group commented, “The work to complete the two drives of 60 m and 57 m long, respectively, completed using 700 mm diameter HOBAS jacking pipe, was executed in a safe and efficient manner and on time despite encountering an obstruction on one of the drives. Trenchless Solutions used its professionalism and expertise to assistance in finding a solution to this relatively minor problem. We would have no hesitation in employing them (TSL) on future contracts.”
For Trenchless Solutions Ltd, Steve Varley, managing director said, “The new technology we now have available with the Perforator pilot auger boring system has enabled us to utilize this methodology to complete what would previously have meant the use of a different technique. The experienced gained using the new Big Bore system now enables us to offer clients a much broader installation range using the pilot guided auger technique and makes us one of very few contractors with this technology in their contracting arsenal. This could open up a whole range of projects and applications which previously not open to the use of pilot guided auger installations.”
The guided auger boring machine that was used for the installation was based on a PBA155 system complete with an HS56 power pack, pilot rods, augers and casings suited to the installation of the DN700 GRP HOBAS jacking pipe. The equipment was originally supplied by Sheffield-based Perforator Ltd. The unit used however now offers a much wider range of installation capacity and in this form is known as the PBS-155 Perforator Pilot Guided ‘Big Bore System.’
What was particularly unusual about this installation was that the Perforator PBS-155 pilot guided auger boring system was used to install such a large diameter pipe.
In this instance however, developments on the Perforator guided auger system used have meant that, with the correct tooling, the system can now install diameters in excess of 1 m diameter without deviating from the pilot bore course.
The Perforator ‘BIG BORE System’ has recently been added to the Perforator product range following successful operations in Ireland, Ukraine and the U.K. mainland.
Big Bore Pilot Guided Auger Boring has been specifically designed to enable the installation of large diameter drainage and service pipes DN600 up to DN900 or 1,200 mm o.d.
In the past, this was only possible by carrying out and extra intermediate drill pass to upsize from 300 mm OD to a finished OD, whereas use of the PBS-155 system enables the finished o.d. to be bored directly following the pilot bore, which can increase productivity by at least 25 percent and requires much less tooling on site.
The Big Bore system has a unique 10-m captivation coupling between auger, cutting head, pilot rods and drill casing, which ensures that the pipe line follows exactly the original pilot bore. Previously large diameter pipes would attempt to steer away from the pilot bore eventually breaking free and causing the bore to fail with potentially catastrophic results.
Other advantages of the Big Bore system include:
This system is part of Perforator’s new range of Pilot Guided Auger Boring machines which have been designed with over-torque drives and high thrust jacking units that enable the rig operator to simply calculate that the rig will achieve the target length and diameter prior to commencement of boring operations, or even at the design stage.
The drill carriage is equipped with multi-speed options that produce faster drilling times and even faster retraction times without the need for secondary retraction devices, winches etc. which in turn speeds up the boring process