Discussion. Design and Construction of Deep Water Quays at Dar Es Salaam and Mombasa.

Abstract

Dar es Salaam, as well as being one of the ports for Zaire, also serves the two small states adjacent to the NW corner of Tanzania, Rwanda and Burundi.60. When tenders were called for Dar es Salaam, tenderers were allowed to submit alternative designs or materials, but the Herkules jointed pile offered by the successful tenderer was the only alternative put to the Consulting Engineers. The joints were, in 1967 when the contract was let, a new concept. Nowadays they are well known and there are other similar types of joint. The idea of a jointed pile avoids the problems of handling long, heavy piles and allows flexibility in the length of piles without having to predetermine exactly the final required lengths of piles. At Dar es Salaam they were made 40ft long for the bottom and middle lengths and 10,20, 30 and 40 ft long for the top lengths. The concrete strength recommended at the time by the supplier of the joints was 5600 Ib/sq. in. which proved adequate, although currently the recommended strength is 7200 Ib/sq. in.61. In $ 17 reference is made to the tolerance built into the manufacture of the joints and to the flexure in the piles of as much as 1) inches in 40 ft. This is 1 in 320, and the Swedish code allows the two halves of the joints to be out of square by as much as 1 in 150. Fendering, bollards and ladders at Dar es Salaam were similar to those installed at Mombasa.62. As at Dar es Salaam alternatives could be offered by tenderers for Mombasa. The only alternatives offered were caisson designs but neither of the two offers was cheaper than the conforming design by. Sir Lindsay Parkinson and Co. Ltd.63. Corrosion is mentioned in $41, and the tests carried out showed that below water level the rate of corrosion was about 0.007 in.!year with about 0,015 in./year in the splash zone.In the original design of 1966 it was proposed to use Rendhex NO. 4 piles, the thickness of which is 5 in., and if one third of the thickness were allowed to corrode their life would be about 26 years. The Client required a life of 40 years and the thickness was to be increased by in. In the event Mannesmann tubes were used and the lower lengths were thickened by 5 mm and 54 mm to give the required life. 64. The blasting of the hard shale of the harbour bed, normally 36 holes at a time, required on average 34 Ib of explosive per hole or slightly under 2 Ib of explosive per d .65. Berths 7, 8 and 9 at Dares Salaam and the berths at Mombasa are designed to take container traffic. The Client also wanted wider quay aprons than had previously been the case at the two ports and at Dares Salaam the raker piles incorporated to take fender blows and bollard pulls were used to take the seaward columns of the transit