TUNNEL UNDER THE RIVER.

New Zealand Herald, Volume LXV, Issue 20136, 22 December 1928, Page 5 (Supplement)

TUNNEL UNDER THE RIVER.

DRIVES RIGHT ACROSS BED.

CRITICS STATEMENTS WRONG.

Referring to the tunnel under the river, Mr. 'Holmes says that owing to fissures being encountered, " the leakage of water into the tunnel caused further work to bo abandoned, and the tunnels were never connected." The last phrase is both incorrect and misleading, since the tunnels were virtually connected, and the gap between them was not under the river, as would bo presumed by anyone without knowledge of the works or access to the plans illustrating it. The tunnel was driven in two sections from shafts sunk on each side ot the river, some 220 ft. apart. The drives were not made toward the middle of the river, but from the left-hand side tho tunnel was driven completely under the river and for ''a distance of 40ft. beyond the right-hand bank of tho river, at which point it came within 2ft. 6iu. of a short tunnel 20ft. long from the shaft on the right-hand bank. Mr. Holmes particularly quotes a passage in the contract specifications, stating that tho shafts were " almost connected," but the gap was only 30 inches thick, and its position and dimensions are dearly shown on the accompanying plans. This small block was left for a further test of the permeability of the rock, which hud already been the subject of prolonged and various laboratory experiments. In case there might be something iu tho nature of a fissure even in this small width, a bore hole was put through and disclosed homogeneous rock throughout. This partition of rock was subjected to the pressure of about 60ft. of water for a long period. Tho result was nil. ' ' v ■ The suggestion that the tunnel under the river' was abandoned on account of tho influx of water has no foundation whatever. That is confirmed by tho 1921 commission's report, which states that tho drive, though only 14ft. below tho river, " was, when inspected, free from defined leaks, except at one point, which was not beneath the actual river water.'' Actually, only two small cracks were encountered in this tunnel. They varied fiom one-I'.alf to three-quarters of an inch in width, and wero entirely filled with a material of soapliko consistency, known as pinguite. The leakage into the tlrivo jvas inconsiderable^