The Kielder tunnels are part of the Northumbrian Water Authority's Kielder Water Scheme and constitute the major element of an aqueduct linking the rivers Tyne, Wear and Tees. The 32 km length of hard rock tunnel traverses a varied sequence of sedimentary Carboniferous strata with limited occurrences of intrusive igneous rocks. Full-face tunnel boring machines were used for most of the tunnel length, with shorter sections being driven using drill-and-blast methods and a roadheader. The Report describes the site investigations undertaken and how the information gained was used to assess the suitability of alternative excavation and support methods. Conditions encountered during construction are compared with predictions derived from site investigations; discrepancies are discussed and means whereby these might have been reduced are considered with the intention of facilitating good future site investigation practice. The principles and operation of the rock classification system used for payment for machine excavation are described. This system provides a useful means of assessing the overall accuracy of the site investigation deductions for much of the tunnel length. (A)

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