A guided boring machine (GBM) was used in conjunction with an auger boring system to complete the 90 metre 450mm bore under the retail store. The bore facilitated retrofitted electrical infrastructure to be linked via the shortest possible route.
The direct line between the existing and retrofitted installations travelled under the store and across the existing car park where a future multilevel car park is under construction. Although it was the most direct route this alignment still presented several challenges both existing and under construction.
To make installation possible, the line and grade of the bore had to be guaranteed to preserve the buildings existing pipe work and avoid several piers and footings under the store and new multilevel car park. Microtunneling is currently the most accurate pipeline installation method available to the civil construction industry with line and grade tolerances of +/- 25mm. The accuracy of the GBM pilot enabled installation of the NB450 steel sleeve to the exact location required eliminating the use of oversize pipe to allow for adjustment of the conduits. Cost reductions were realised in cable sizing and quantity and also excavation and reinstatement costs.
As well as being the most accurate and cost effective method pilot tube microtunneling offered the least disruption to the retailer as it continued to trade; and avoided any clash with the new multilevel car park development. This microtunneling technique also saved time allowing hand over of the works prior to the Christmas shopping rush. The inconvenience to the retailer and customers was reduced to nil.
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