Motukawa Tunnelling Machine
Engineering Plant (eg railway, locomotive, car, plane)
The tunnelling machine used in 1924/5 for the construction of the headrace tunnel for the Motukawa Power Station was possibly the earliest use of a tunnelling machine in New Zealand.
The Motukawa Power Station built in 1927 to develop a head of 99 metres between the Manganui and Waitara rivers today generates 4,800 kilowatts and is operated by TrustPower. A scheme devised by H R Climie of Messrs Climie & Sons was adopted by the original owners, the Taranaki Electric Power Board in April 1923. The Board also adopted the proposal of its consultant to purchase a tunnelling machine from Sir William Arrol & Co of Glasgow, Scotland.
The rock to be tunnelled was papa with a tunnel diameter of 2.13 metres (m) and a length of 2875 m, starting from a surge chamber excavated in the hill above the penstock slope at the downstream end. The machine arrived in New Zealand in January 1924 but could not commence tunnelling until September 1924 due to faults in manufacture and supply of cutters. The latter was ultimately replaced with cutters made in New Zealand.
Initial progress in grey papa was good at one metre per hour, including all stops, with a maximum advance of 1.5 m per hour. However boulders were soon encountered. These slowed progress as they required hand excavation and sometimes occurred every 1.5 m. The largest boulder was 7.6 m long.
Machine tunnelling continued until 2080 m of the tunnel had been excavated in November 1925. At this point the ground conditions had changed to a silty material and several cave-ins occurred. Further work on the tunnel was carried out by conventional means using heavy timbering, the overlying country being swampy. The part of the tunnel in rock was gunite lined and the remainder concrete lined.
A shaft was constructed to enable the removal of the tunnelling machine which was accomplished by May 1926. The tunnel excavation was completed in August 1926. The Board offered the tunnelling machine for sale. Some auxiliary equipment was sold (cement gun and air compressor) but the machine itself was used as a source of parts for other operations of the Board so that no recognisable parts remain.
(The above account has been written from the publication Motukawa Power Station published by the Taranaki Electric Power Board and printed by the Stratford Press)
Taranaki region near the Waitara River
Nature of Engineering
Electrical Power Generation and Distribution