A bore design was developed that was acceptable to RailCorp, whilst fitting within the narrow 5.5 metre easement and meeting the required depth of cover under the Caltex multi products pipeline.
The bore design called for 8 parallel bores with a total of 16 x 180mm and 9 x 63mm PE electrical conduits to be installed. In order to accommodate all the conduits within the narrow easement, an ‘over and under’ design was proposed with the 11kV conduits installed as single bores and the 33kV conduits in a trifurcated arrangement. Tight tolerances of +/- 100mm horizontal and +/-200mm vertical alignment on all bores added to the complexity and accuracy of the project.
UEA utilised its 25 tonne Vermeer D50 x 100 to undertake the bores. Geotechnical information supplied by the client suggested medium to high plasticity sandy clay, extending to siltstone, which would become stronger and less weathered with depth. A comprehensive survey was provided by the client with each bore line pegged at five metre spacings along the entire route. Beaver tail reamers were utilised for the pre-reaming passes in conjunction with a comprehensive mud program, designed to reduce the swelling of the reactive clays and to help carry out solids contained within the mudstone.