The Wainuiomata Tunnel was planned to improve access to the Wainuiomata Valley in the Wellington region of New Zealand’s North Island as part of a scheme to commence residential development there in the 1930s. Construction started in 1932 but was halted several years later when only partly completed due to a lack of funds brought about by economic depression.
The tunnel was never opened to road traffic, and other than a brief stint of military service during World War II, remained unused until sold in 1975. Thereafter it was completed as a utility tunnel, initially carrying only a water pipe, but later other services were added.
History
Background
Wainui-o-Mata Development Limited was formed for the purpose of developing the Wainuiomata Valley through the acquisition of land, subdivision, and sale of residential lots. An important part of the project was the construction of a tunnel linking the Hutt Valley and Wainuiomata Valley for improving access to the new settlement.
Planning
Like the then recently completed Mount Victoria Tunnel in Wellington, the Wainuiomata Tunnel was designed to allow for two lanes of opposing general vehicular traffic with a raised pedestrian pathway on the north side. Starting from a point near the industrial park at Gracefield, it would rise on a gradient of 1 in 15 to emerge at the foot of the hills in Wainuiomata near the existing hill road. It was to be wide, high, and have a length of . The footpath would be wide, above the floor of the tunnel.
The Railways Department became particularly interested in the tunnel and realised it would be advantageous for them to obtain the right to access the tunnel before their competitors were able to establish competing services. To this end, they entered into an agreement on 1 October 1928 with Wainuiomata Development for the sole right to operate “motor or electrical passenger transportation” through the tunnel between Wainuiomata and Wellington City, Lower Hutt, or Petone. The agreement also committed the parties to the following: The Company would ensure that the tunnel was sufficiently wide enough to enable two motorbuses to pass each other. The Company would make available to the Department suitable land for terminal facilities in the Wainuiomata Valley. The Company would reserve a wide strip of land down the centre of the main road through the new settlement. The Department would commence operation of a motor transportation service between Wainuiomata and Wellington City, Lower Hutt, and Petone once the Valley sustained a permanent population of at least 50 families. The Department reserved the right to establish and operate an electrical tramway from Gracefield Road, through the tunnel, and down the centre reservation on the main road at its discretion to supplement the motorbus service.
Wainuiomata Development called for tenders to construct the tunnel in October 1931 and awarded a contract for the same to Templeton Tunnel Construction Company.
Construction
Work commenced on 25 January 1932 using subsidised labour from a work relief scheme to find employment for those affected by the economic depression. A workers camp was erected; flat land was cleared around the portal on which buildings were erected for the workshop and powerhouse. Plant included an electric motor for running air compressors, ventilation, and the equipment used to apply the concrete lining to the completed tunnel walls. Formwork for the tunnel portal was assembled and the hillside prepared for the building of the portal. Additional men were due to start work at the site after 1 February.
Unlike the standard practice for tunnel construction in which at least two faces are advanced simultaneously (either end of the tunnel), it was decided in the case of the Wainuiomata Tunnel that work would only take place from the western end towards Wainuiomata. This was done for drainage; on such a steep grade it was easier to work uphill and let the water that flowed into the tunnel drain out naturally rather than have to pump it out (as would be the case if they had worked downhill from the Wainuiomata end). It was noted, however, that if needed up to three 8-hour shifts per day could be deployed at both ends of the tunnel to improve progress. The men working in the tunnel found that the ground they were excavating was not ideal for tunnelling, and often encountered soft earth or “rotten” rock.
The first pass on the tunnel shaft was not to excavate down to the full depth of the completed tunnel. Rather, an additional of earth was to be removed before the sealed roadway could be laid through the tunnel.