Airlift for bridge

Press, 12 April 1978, Page 7

Airlift for bridge

The airlift of earth-mov-ing machinery to the Lower Swing Bridge over the Hooker River last week was a difficult operation, said ■ the resident engineer of the Ministry of Works and Development in South and MidCanterbury (Mr E. R. E. O’Toole). A small-track back hoe had been used to excavate the two anchor blocks on the east side of the Hooker. The machinery, weighing 1500 kg, was broken down to 1000 kg to enable a Lama helicopter o'f Helicopters N.Z., Ltd, to lift it. Since the end of December, 1977, wire ropes had been reinforced, limiting access for visitors using the bridge to one at a time — a restriction still in force. Mr O’Toole said The Ministry was constructing four new anchor blocks. The work involved the excavatioh of 10 cu. m at each block with about 5

cu. m of concrete, and steel stays from the anchor blocks. It was hoped that this would be connected to the existing structure before the winter. In the spring the entire bridge would be replaced with new towers, new, wire ropes, new timber platforms and guide wires. The bridge is about Ikm up the Hooker Valley over ground on which it is impossible to transport heavy machinery. “Some difficulty was experienced in carrying out the excavation because of large boulders and an explosives expert is breaking them up,” said Mr O’Toole. Extreme care had to be taken because of visitors. The total length of the span of the new swing bridge would be 70m. and the length between the anchor blocks 130 m. Only one person at a time would be allowed on the bridge until the new structure was built. The new bridge was being

built on the old site so that the old, strengthened bridge could be used for the conveyance of component parts for the new bridge and also act as scaffolding. Considering the difficulties the ministry was experiencing in excavation work and the problems it was likely to encounter in replacing the bridge, Mr O’Toole said he had the utmost admiration for those who built the original bridge. “It was done by hand. There was little suitable machinery, and every credit should go to the pioneers who built a bridge which has given such excellent service,” Mr O’Toole said. The old anchor blocks were .of Australian hardwood. The timbers were laid horizontally about 1.829 m to 2.438 m deep. The wire ropes were linked round lhe timber and boulders were placed over the timber in the excavation to give added weight and stability.