Glass Reinforced Plastic Bore Casing for Large Diameter and Deep Bores
This report was produced for the Urban Water Research Association of Australia, a now discontinued research program.
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Glass Reinforced Plastic Bore Casing for Large Diameter and Deep Bores
Report no. UWRAA 12
July 1990
Synopsis
In Western Australia mild steel pipe used for bore casing lasts for as little as four years. On average the collapse pressure strength of steel casing is reduced through corrosion by approximately 10% per year.
Production bores used by the Water Authority of W.A. for Perth’s water supply range from250 ND by 40 metres deep costing about $40 000 to replace, to 500 ND by 1100metres deep costing about $900 000 to replace.
The alternative materials to mild steel for bores of this size are fibre reinforced plastics (FRP) and stainless steel. Stainless steel is approximately twice as expensive to purchase as GRP (glass fibre reinforced plastic) and twice as expensive to install due to factors such as the equipment required to handle the weight and the jointing costs.
The joints on the previously available GRP casing, however, were unreliable and unsafe to use in deeper pressure grouted bores particularly of larger diameter. Many construction failures occurred for which the drilling contractor was unfairly expected to assume responsibility.
The aim of this project was to improve the reliability and capacity of these bore casing joints to enable the safe use of GRP casing to at least 400 ND and 500metres depth.
Although at the conclusion of this successful project, development of GRP casing to its full potential is not complete, the aims of developing reliability and extending the size and depth range have been met.
Tables1 and 2 give the recommended maximum depth ratings for the newly developed GRP casing joints for pressure grouted bores using the test results from development to December 1989.
The capacities and depths given in Tables 1 and 2 have been calculated using a load factor of 1.5.
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