| TRENCHLESS TECHNOLOGY


Commencing the auger bore upsize of the pilot bore


Pilot auger boring success


AS PART of the ongoing €19.5M Carlow Town Sur- face Water Drainage Scheme, Flood Relief Scheme Phase A and Water Conservation Pro- ject Phase 2, which started in May 2010, a section of 950mm diameter sewer pipe- line was required to be in- stalled over a 40m length in a very difficult access location. Positioned in a narrow side street in Graiguecullen in Car- low, the location was deemed


When specialist contractor Conwell Contracts was brought in to assist on a drainage scheme in Carlow, it proved a memorable challenge.


to be inaccessible using the open cut techniques previ- ously utilised on significant tracts of the project. Given the limited space and a high density of existing other ser- vices that would have had to


have been negotiated using the open cut option, it was de- cided the pipeline could only be installed using a trenchless technique.


Main project contractor Wills Bros brought in spe- cialist


contractor Organised by Supported by Conwell Gold sponsor


Contracts early in the plan- ning phase for the 40m long section to offer advice on potential alternatives. It was decided the best option for the Graiguecullen works was to utilise the pilot auger bore technique for the installation. Pilot auger boring is an es- tablished technique but is usu- ally applied on installations of up to 600mm diameter. The 950mm diameter requirement for the Graiguecullen installa- tion meant the project would bring with it significant chal- lenges even for experienced contractors.


Speakers include


Richard Ackroyd Chief Executive Scottish Water


Barbara Frost Chief Executive Water Aid


Anthony Cox Head, Environment and Economy Integration OECD


Alan Sutherland Chief Executive Water Industry


Commission for Scotland


Nigel Earnshaw General Manager Veolia Water Scotland


David Pirie Director of Science and Strategy


Scottish Environment Protection Agency


Mark Powles


Chief Executive Offi cer Business Stream


Chris Banks Chairman Scottish Water Horizons


Conwell employed its Perforator PBA155 model pilot auger boring system equipped with the Big Bore System (BBS) to complete the installation. Supplied by Sheffield-based Perforator, the company also provided an establishment crew as this would be the first time that Conwell had undertaken a project of this diameter with the BBS.


Addressing the roadmap and barriers to building a Hydro Nation Attend this one day conference to:


• Be at the forefront of Scotland’s development as a Hydro Nation • Gain insight into Scotland’s excellence in governance and asset management


• Find out what technological innovations will shape the future of catchment management and wastewater treatment


• Join the debate of how to balance asset optimisation with customer engagement and environmental protection


• Make new connections with like-minded partners across the water industry


Book before 10th August to save £60 www.water-scotland.com


In association with 12 | WET News | July 2012


As with all pilot auger op- erations the installation re- quired construction of both a start shaft to accommodate the boring system and a re- ception shaft at the end of the bore route. Whilst the recep- tion shaft was easy to access − it was located at a junction of several of the surrounding narrow streets − the start/ launch shaft was a different proposition. Both launch and reception shafts were to be sunk as sheet pile coffer dam constructions.


Located between a resi-


dence and a block of flats in a narrow street, the start shaft was difficult to exca- vate because the manoeuvring room for the excavator used was limited and the machine could not complete a full 360° swing.


After initially sheet piling the required area and opening the shaft to an initial depth it became impractical to use a large


excavator to com-


plete the shaft sinking work. A mini excavator was used to complete the dig with the larger excavator simply re-


moving spoil from the centre of the excavation.


The shafts were sunk to a depth of about 4.3m, with the start shaft having a concrete base and a rear thrust wall included as part of the con- struction. At the front of the shaft where the bore would start, a concrete wall was in- stalled with a circular access for the boring machine to pass through.


Once the shafts were pre- pared the boring system’s jacking unit was positioned on the floor of the launch shaft and anchored into posi- tion on the approximate line and level of the required bore. Establishing alignment prior to commencing the boring op- eration minimises the require- ment to apply major steering adjustments to the boring head as the pilot bore takes place, such that steering ad- justments that do take place are simply to keep the pilot head on or as close to the de- sired alignment as possible. The completion of the pilot bore went smoothly with the pilot head arriving on target at the reception shaft. Once completed the pilot bore acts as the guide for the upsizing of the bore to the final desired diameter for the installation of the final product pipe. To achieve the bore upsize the auger head and hollow stem auger string were placed inside steel pipe which was advanced along the bore path a section at a time with each subsequent steel pipe length being welded to it preceding length once it was buried in the ground by advance of the jacking frame. This process was repeated until the auger head arrived at the reception shaft.


Once this second phase of the installation was com- pleted the auger string was removed from the bore at the launch shaft using the jacking frame to retrieve the auger sections.


To complete the installa-


tion each 2m long product pipe was placed in the jack- ing frame and pushed into the bore. As the product pipe advanced the steel casing pipe installed during Phase 2 of the pilot auger process was extruded into the reception shaft where it was cut and re- moved.


The next length of product pipe was then placed in the jacking frame pushed into the bore. This process was con- tinued until the lead product pipe arrived at the reception shaft. The installation was then complete. n


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28