Paterson, B.R. 1978 An engineering geological appraisal of daylighting proposals for NZR tunnels 22 and 23, Blenheim. Lower Hutt: New Zealand Geological Survey. New Zealand Geological Survey report EG 303 17 p.
Abstract: Transport of large freight containers by rail has resulted in clearance problems in two short tunnels south of Blenheim, and the N.Z. Railways Department is proposing to resolve the problems by daylighting the tunnels. Geological investigations of the sites have carried out to determine the nature of the materials above the tunnels and their likely behaviour when exposed in open cuts. The conglomerate above tunnel 23 forms very steep batters in existing open cuts nearby, and should not present instability problems during daylighting. A siltstone with minor gravel which erodes more readily then the conglomerate, is probably present near the south side of the tunnel and should be avoided during construction. The shattered greywacke colluvium which is present above tunnel 22 should be easily excavated, but careful design and construction of the batters will be necessary to prevent erosion. Disposal of spoil could be a problem at this site because of a lack of flat land nearby. (auth)