Geotechnical Design of the Rapahoe Bridge No. 1 North Abutment

Tranz Rail Ltd proposes to build a replacement rail bridge over the Grey River at Greymouth on the West Coast of New Zealand. The north end of the proposed bridge lands at a skew to the existing cut rail line bench. Consequently, a pile is required to support the north abutment and retaining walls are required, perpendicular to the railway alignment at the abutment and along the outer edge of the railway formation north of the abutment, to extend the railway bench on fill. The preferred option for the retaining walls consists of precast panels founded on a reinforced concrete beam cast against and anchored to the rock face. The post tensioning of the anchors and friction between the uneven rock face and the concrete beam provides vertical support.

This paper presents details of the geotechnical design of the north abutment including the investigations undertaken, the ground conditions encountered, selection of the abutment location, options considered, selection of design parameters, load cases considered and detailed design. The design included finite element analysis of the retaining wall.