A trenchless triumph in Lancashire
When a new drainage pipe needed to be installed as part of a flood alleviation scheme in Blackburn, a trenchless installation technique proved ideal for the challenge.As part of a new flood alleviation scheme being undertaken by United Utilities (UU) in Blackburn, Lancashire - through its main contractor, VJ Donegans Civil Engineering - a new 24m long drainage pipe needed to be installed beneath Gorse Street.
The installation, known as Blackburn UIDs, Gorse Street, was to comprise a DN300 gravity sewer laid to precise line and level parameters as set out by UU's design engineers.
Given the urban location and the need to ensure that the grade of the new sewer was maintained it was decided to utilise a trenchless installation technique that could facilitate the line and level control necessary to
successfully complete the installation.
The contract for this part of the flood alleviation work was awarded to Trenchless Solutions, of Wakefield, West Yorkshire, which chose to use a Perforator PBA85 Guided Auger Boring
system to complete the installation. This system was selected from those available on the market because it offered a relatively small operational footprint, which suited well the urban location of the project, as well as having the capacity to handle the ground conditions expected to be encountered at the level of the pipe installation.
The boring rig's line and level control system also meant that the critical line and level requirements of the bore could be accurately and precisely maintained throughout the installation.
Prior to the start of the installation works cable percussive bore holes were used to undertake ground investigation survey using a Dando 2000 drilling rig. This investigation confirmed that the ground at the installation horizon comprised soft to
stiff clay. The Perforator PBA85 guided auger boring machine that was used in Blackburn was a complete system that included an HS56 power pack, pilot rods, as well as augers and casings designed to suit the parameters of the, in this case, 1m long Naylor-manufactured Denlok DN300 clayware pipe chosen for the installation.
Directional control of the pilot bore was achieved using a monitor, an optical system with a CCD camera and a diode target plate.
The PBA85 rig utilised a three pass system to complete the new pipe installation comprising an initial pilot bore that established the accurate line and level of the bore which would be followed by the subsequent installation phases. This pilot bore was then expanded using an auger chain with a cutting at the lead end.
The auger chain ran inside auger casings with excavated soil being removed from the bore to the start shaft via using the rotating augers.
With the bore now at the required diameter the final placement by jacking of the Naylor Denlok DN300 pipe into the bore whilst displacing the auger chain at the reception shaft completed the installation.
The PBA85 guided auger boring rig offers some 850kN of forward thrust as well as a maximum 470kN pullback force and operate from a start shaft or pit of a minimum 2m diameter. The machine will install pipelines from DN150 to DN500. The unit can be extended by up to 5m where circumstances require and are permitted to handle the installation of longer pipe section in one operation.
Work started on the 24m long sewer installation on November 22, 2010 with the installation being completed two days later with no specific problems being encountered during the course of any phase of the work.
The use of the trenchless system for the installation also meant that despite the urban setting local residents and businesses were not inconvenienced in any way by the presence of the works.
A spokesman for VJ Donegan says: "We have used Trenchless Solution on several contracts and have been pleasantly surprised by their performance, attitude and flexibility.
"The company has in the past overcome unforeseen problems and successfully completed contracts with no additional costs. We would not hesitate to employ their services on future contracts."
Trenchless Solutions, a relatively new company having been established in February 2009, is a No-Dig contractor working throughout the UK and Ireland.
It offers expert solutions whilst working with clients from project conception through to completion; the company provides its expertise for safe, innovative and cost-effective underground installations.
Services include: Guided Auger Boring, Horizontal Directional Drilling, Pipe Bursting, General Auger Boring and Moling for buried
services such as Drainage, Sewers (including the use of Naylor Denlok clayware pipe), Water, Gas, Communications, Electricity, Chemical and Oil installations under Roads, Rivers, Buildings, Structures, Existing services and Railways.
According to Steve Varley, the director of Trenchless Solutions, who has some 15 years' experience in the trenchless industry: "Our experience in working on varied No-Dig projects gives us a real knowledge of the challenges our customers' face every day.
"We know how important it is to look at our customers' individual needs when helping them with a solution no matter what size the job or how demanding it may be."
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