THE MERSEY TUNNEL

New Zealand Herald, Volume LXXII, Issue 22056, 12 March 1935, Page 11

THE MERSEY TUNNEL

ENGINEERING TRIUMPH ADDRESS TO ROTARIANS An impression of the difficulties and triumphs of the engineers responsible for the contruction of the great Mersey tunnel was given by Mr. C. Trevithick at the weekly luncheon of the Auckland Rotary Club yesterday. Mr. Trevithick's description was aided by a number of plans and pictures thrown on the screen. The work on the Mersey tunnel, he said, was begun in 1925 and completed after nine years at a cost of between £8,000,000 and £9,000,000. The main tunnel was 2i miles long and the addition of the two smaller subsidiary tunnels brought the length up to almost three miles. Under the river the tunnel was 170 ft. below high water mark, and it was 44ft. in width, providing for four lines of traffic. The covering of rock above the tunnel was generally about 30ft. in thickness, but in sornn places it was only about 3ft. During the construction of the tunnel the seepage was considerable, and for every ton of rock excavated 26 tons of water had to be pumped back into the river. The top half of the circle of the tunnel was completed first and then the lower half. For 2J years tons of rock was taken out every minute. The ventilation scheme cost £1,500,000, and it was controlled from six large buildings, three on either side of the river. The bad air was drawn out from the roadway and discharged 200 ft. into the air, and fresh air in similar quantity was pumped into the passageway underneath the road. The ventilation was controlled from a building in Liverpool, where it was known exactly how many cars were in the tunnel and what was the carbon monoxide content of the atmosphere. The great air-fans were regulated accordingly-