. MILLS M r Page, M r Curtisand M r Mills Regarding the test on the sheet piling, some additional information may be of interest. The loads in four of the tie rods were monitored: two of these rods were instrumented at both quay and anchorage ends and two at the quay ends only.Figs 21 and 22 show that the loads in the quay ends were quite low initially at only 100-200 kN and it was not until the final placing of the 2 m of Thanet sand compacted in 30 cm layers, that the loads increased to 400-500 kN, about two thirds of the 700 kN design load. From Fig. 22 it appears that initially the anchorage loads were dissipated in friction along the rod without any load being transmitted to the anchorage, the rods being under temporary compression at this end.81. A Stothert & Pitt 6 t vibrating roller (developing 96 t impact load) was used to compact the sand and this clearly helped to generate more realistic earth pressures transmitting loads of up to 40 t to the anchorages. If the design had been of the form in which the sheeting was driven entirely through existing soil with the face dredged after completion it is possible that the anchorage loads would have remained low, suggesting an unnaturally high factor of safety.82. Nine piezometer tubes were also installed to monitor movement of groundwater level. Only one of these continued to function throughout the construction period and this happened to be nearest to the instrumented sheet piles. A typical result is given in Fig. 23. This shows groundwater level following the rising tide very closely, which may not be entirely accurate, and could have been distorted by the presence of the piezometer tube itself. With the falling tide, groundwater level is held just below mid-tide and this is probably a true indication of the situation at this section. The design was based on groundwater being at mid-tide level and to that extent appears to be slightly conservative.M r J. N. Black, PLA, Tilbury Docks There were several reasons for choosing a site on the riverside rather than within the dock. The third-generation container ships were just beginning to be built, and we felt it would be advantageous to have a facility which obviated the need for them to go through the lock : the time-saving was important, as most of the large ships using Tilbury have to use the tide for the depth of water. Another reason was

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

The Ballard Pier extension was constructed at the same time as the Bombay Dock expansion scheme, which was started in 1964 and finished around 1970.58. Possibly the most interesting part of the Paper is that concerned with the design and construction of the quay. Although there are certain standard approaches to the design of quays, the optimum solution for a given set of conditions may not be easy to find. Horizontal loading differs considerably from one quay to another, and with the introduction of containers vertical loading has considerably increased in the last few years. Quay heights also vary greatly, not only to accommodate different vessel sizes but also to take account of tidal ranges. Other factors affecting the design are the condition and level of the sea bed and the exposure of the berth, but the most important one is undoubtedly the soil properties, both of the foundations and of the back-up material. The question as to whether the quay is to be constructed under water or in the dry has to be decided and the use of monoliths, caissons, cofferdams, cylinders, sheet piles and suspended deck construction must all be considered. 59. The design described in the Paper, which involves a method of construction which has not been frequently used, might be developed with advantage for other locations besides Bombay. The idea of a buttress wall with arches from buttress to buttress has seldom been adopted in recent quay design, which is surprising in view of its many advantages: a block work wall or a mass concrete quay built in a cofferdam would have entailed much more concrete and in consequence would have been considerably more expensive. The method adopted requires little heavy plant, an important point when the length of quay is limited and its cost cannot be spread over a long length of wall.60. The customs hall roof was originally designed to be of self-supporting aluminium curved segments which would have made a very economical form of construction. Unfortunately, the Indian aluminium companies refused to roll curved segments, and conventional trusses had to be substituted.61. The Architects for the central concourse and customs sheds were Mathew Ryan and Partners. Their names should be added to the Acknowledgements in the Paper. Mr D. Jones, Chief Engineer, British Transport Docks BoardThe Paper makes little reference to the additional trade needed to justify the extension of Ballard Pier, and perhaps the Authors can give some information on this point. In particular I should like to know whether the revenue from such additional trade was regarded as being sufficient to support the investment, or whether there is an element of subsidy in the investment in the facilities of the Port of Bombay.63. I was very interested in comparing the design of the dock walls with that in the extension of the Alexandra Dock (now Indira Dock), described in earlier papers.1*2

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