PORT CHALMERS GRAVING DOCK.

New Zealand Mail, Issue 13, 22 April 1871, Page 2

PORT CHALMERS GRAVING DOCK.

[From the Otago Daily Times.]

This' noble and useful structure is completed so far as the contractors are concerned, and the dock gates are shut.* Some extra work outside the gate, and not provided for in the contract, delayed the removal of the coffer dam, but a beginning has been made towards accomplishsng this object, and the dock is expected to be opened for the overhauling and repair of vessels during the course of next week, when the ship Agnes Muir will probably be taken in as the first vessel. Considering the importance of this work, not only to Port Chalmers, but also to the province and colony generally, it will not be out of place to give a brief account of the manner in which it has been constructed. The dock was begun on the 16th J-uly, 1868, on which day his Honor the Superintendent (Mr Jas. Macau drew), 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 direction 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 other 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 on 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 water-tight. 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 wafer 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 a 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, leaking sluices, which had been fiied as a proviso against accident, were opened, and the dock again filled, A row of sheet piles was then drivan about four feet outside of the orig;nals, level with low-water mark. Part of the silt haviug 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 shoie end of the dock, and continued outwards to the entrance. The proper depth being attained, a concrete bottom of two feet thick was laid, on which rest pitchers of two feet deep oh cement, and grafted 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 out step by step to 68 feet at the top or coping stone. The stone was laid against sixteen 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 contractors was slid down on the ways to the works. . The earth for reclamation was found equally handy in the ground adjoining the head of the dock. The cement used, 1400 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 horse-power, each capable of working up to a higher power, were all imported from home, together with the 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 of jarrah, or, as it is usually called, Swan River mahogany, a wood impervious to worms. The entrance is fifty 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 forty-five feet 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 stones weigh over seven tons. The opening of the gates, which weigh twenty-four tons, is effected so simply and perfectly that they can be opened and thut by one man. The stone work is rough ashler outside, but smooth on the bottom and top, and firmly bound together with cement and backed by concrete. From the very commencement the contractors have worked in a most systematic manner in all their doings, and although the men were atone 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.