PORT CHALMERS GRAVING DOCK.

New Zealand Mail, Issue 18, 27 May 1871, Page 6

PORT CHALMERS GRAVING DOCK.

This dock was begun on the 16th of July, 1868, on which day his Honor the Superintendent (Mr Jas. Macandrew), wheeled the first barrowful of earth, and capsized it into the water in close proximity to the present dock. The Hon. Julius Vogel and several members of the House of Representatives, and a large concourse of persons were present on the occasion. The ceremony went off with great eclat, and the landed proprietors of the Port thought that if their fortunes were not made, it was at least a step in the right directioh towards so desirable an object. His Honor, after performing his laborious task with the wheelbarrow, declared the construction of the dock to be begun in an appropriate speech. Mr Vogel followed, bandying compliments with his Honor; and speeches were also made by members of the General Assembly and others. On the 13th of the following month, the contractors (Messrs Connor and Mackay), commenced work in earnest, first at the quarry adjacent to the site, and then reclaiming land from the shore end of the jetty, on the beach line, to the full extent of the dock on both sides. That being completed, the next operation was to put in quay heads, or timber wharves, at the extreme end, to serve as a breastwork for the outer portion of the earthwork which forms the sides. A coffer dam was next constructed by a single row of piles of native timber in a semicircular shape, each pile being straightened and made so that the joints should radiate to a common centre. Battens of similar wood, measuring four inches by two, were fastened to one side of each pile, forming an open groove from top to bottom of six inches by two. This groove was afterwards filled with straw and rammed hard down to make it watertight. This work was merely to serve the temporary purpose of keeping the water out until such time as the inner joints could be properly caulked in the usual way. It was, however, afterwards found that the straw excluded the water so thoroughly, that it was made a permanent portion of the structure. After standing twenty months the joints were found to be as good as they were on the first day when the water came upon them. The water was then pumped out of the dock but as the leak in some rotten or shingly gutter was discovered springing up underneath the piles, in order to prevent damage to the whole of the dam by leakage, sluices, which had been fixed as a proviso against accident, were opened, and the dock again filled. A row of sheet piles was then driven about four feet outside of the originals, level with lowwater mark. Part of the silt having been removed between the two tiers of piles, the vacancy between them was puddled with clay. The dock was then pumped out again, and the coffer dam proved all but tight, there being only a slight weep, which continued throughout the whole work at high water. This, however, was kept down by the aid of temporary pumps, and the men were able to go steadily on excavating for the concrete bottom. This work was commenced at the shore end of the dock, and continued outwards the entrance. The proper depth being attained, a concrete bottom of two feet thick was laid, on which rest pitchers of two feet deep on cement, and grutted with cement. On the left hand side as you enter the dock, heavy boulders and solid rock to the length of 150 feet, and a breadth of 60 feet, were come across, and had to be blasted to beneath the level of the concrete, greatly retarding the progress of the work. - A concrete bed was laid over this rock, so as to prevent springs from bursting upwards. While the bottom of the shore end was being completed, the sides were begun, the start being made at 41 feet, and merging step by step to 68 feet at the top or coping stone. The stone was laid against 16 feet of concrete on the sides in the lower part, merging to four feet on the top, until the outer and inner invert of the bottom were reached, when a deeper stratum of concrete was laid. The stone, as previously stated, was all procured from the quarry on the hill adjacent, and by a simple contrivance of the eon* tractors was slid down on ways to the works. The earth for reclamation was found equally handy in the ground adjoining the head of the Dock. The cement used, 1,400 tons in quantity, has been of the best Portland. It is estimated that 90,000 cubic feet of stone have been used. The metal for the concrete was broken by a steam stone-breaking machine. The iron-work for the gates, centrifugal pumps capable of pumping out the Dock in three hours and a-half, boilers, and two engines of 15 horsepower, each capable of working up to a higher power, were all imported from home, together with cement, at a cost of nearly £IO,OOO. The contract was close on £49,000, and as many as 140 men have been employed at one time on the works. The gates are built ofjarrah, or, as it is usually called, Swan River mahogany, a wood impervious to worms. The entrance is 50 feet wide. The keel blocks are also of jarrah. They are placed and secured by dogs in a line with the sill of the Dock, thus giving a space of 45 feet long for the bilge of any vessel that may enter. The hollow coign stones for the gates to swing against weigh from five to seven tons each, while the gudgeon Btones weigh over seven tons. The opening of the gates, which weigh 24 tons each, is effected simply, and perfectly that they can be opened and shut by one man. The stone work is rough ashlar outside, but smooth on the bottom and top, and firmly bound together with cement and backed by concrete. From the very commencement the contractors haVb worked in a most systematic manner in all their doings, and although the men were at one time like a hive of bees, not one could interfere with the other.. The quality of workmanship in the Dock will bear comparison .with that in many home docks that cost double the money.—“ Daily Times.”