Discussion. Karachi Harbour-East Wharves, Reconstruction of Quay.

Abstract

DiscussionMr G. A. Wilson (Chief Engineer, Port of London Authority), in opening the discussion, said that on first looking at the Paper he had been delighted with the design. It was undoubtedly most interesting but on reading the Paper the problems which such an elegant design had presented were brought out and he began to wonder if it were as satisfactory as the first glance had suggested. 72.The old work, built with screw piles, had lasted:45 years, and as a dock engineer he thought that could be considered an excellent design because after 45 years alterations to meet more exacting conditions were generally needed. Those who made the screw pile design could be well satisfied with their achievement.73. The Authors pointed out that because of the generally corrosive and destructive conditions they could not recommend any of the normal designs and adopted prestressed concrete but he wondered if, when the job was finished, they remained content with the method of construction. He had a practical interest in the cost of the design because he was about to build a quay wall about 48 ft high where the duty would be similar. He proposed to continue with the design described in I.C.E. Paper No. 62511, No. 1 Berth, Tilbury Dock, in which costs were quoted. The Authors' design involved a good deal of divers' work and tidal work both of which he always endeavoured to avoid. The Paper stated the cost to be M25 per ft length of quay, but did not say if this figure included the surface of the quay or other work such as crane tracks. In the Tilbury design simple 30 ft square concrete monoliths were sunk into the ground, with a concrete slab top supported on the monolith and cantilevered over the back to make a 50 ft wide surface. The cost of this was M39 per ft run so that allowing for all the variables there did not seem to be any great saving in the prestressed design. The monoliths provided such a very solid wall and quay surface that the design did not fulfil his first requisite, that it should be ready to be renewed in about 50 years; it would probably last 150 years.74. In the Tilbury design the surcharge on the deck was taken as 4 cwtlsq. ft and he noted that the Authors had used 2 cwt/sq. ft but tested to 5. The Authors mentioned protecting the steel in the concrete from the corrosion but did not say what cover had been used. The drawings were small so it was difficult to tell but it seemed doubtful if any greater cover than usual had been possible in the R.C. beams between piles. He was interested by the remark about the synthetic rubber compound to stop leaks in slabs and wondered whether it had been successful.75. There were many interesting records in the Paper, particularly about the testing of earth pressures and he hoped that other speakers would take this point. Information on the number and type of jacks used to get the stress in the cables would be useful. The t Proc. Instn civ.