Water in TBM drives, Delivery Tunnel South, Lesotho Highlands Water Project

Abstract

This paper deals with a variety of related aspects concerning the dealing with groundwater in excavations driven by tunnel boring machine for the Delivery Tunnel South, a section of the waterway tunnel for the Lesotho Highlands Water Project. The paper commences with the design/tender predictions for water it was envisaged may be encountered, the tender methods specified for dealing with that water and the contractual aspects/sharing of risk/payment mechanisms set out in the tender documents for dealing with water. Following on details are provided of information tenderers submitted regarding their estimates of the time required to carry out cover drilling and grouting and the effect on overall TBM advance rates. The paper then concludes with details of actual water encountered, the manner in which the tender specifications were amended in dealing with that water, the actual effect on TBM production as well as the actual construction methods used.