wave height of 4 ft. was used. The effective wave height, which seems reasonable, was obtained from the Sverdrup-Munk formulas for a fetch of 1 mile and a maximum mean wind speed of 70 m.p.h.
The majority of the tank founda- tions, which were specified in princi- ple by Esso. consist simply of crush- ed stone bases shaped to receive down-cone tank bottoms and transmit the bearing pressure direct to the sub- grade, which amounts to about 11⁄2 tons per sq.ft. for a 56 ft. high tank when under water test.
The foundations for the largest tanks each consist of nearly 3,000 cu. yd. of graded crushed rock which was laid and rolled in similar fashion to a road stone. The foundation was finished off with a 4 in. cushion of oil- ed sand on which the bottom plates of the tank were laid.
Foundation design for welded steel tanks of this type is not the same as for buildings or similar structures:
differential settlement can be re- latively large, although there is a limit above which distortion be- comes excessive and structural failure is liable to occur; total settlement can be very large and acceptable until it affects pipework, drainage, etc.;
—it is relatively simple to correct faults that are found to be ex- cessive:
-reinforced concrete raft founda- tions and piled foundations are
extremely expensive for large diameter tanks compared to the costs of the tanks themselves and to the cost of possibly having to rectify a simple foundation.
Marine Facilities General description
as
The marine facilities as built can accommodate tankers of up to 65,000 d.w.t. as well as the necessary small craft for transhipment of products within the Colony. To accommodate these vessels marine facilities shown in Fig. 1 have been provided and a channel is being dredged to the berth to permit fully laden 65,000 d.w.t. tankers to come alongside at all states of the tide.
Loaded tankers will come straight in from the west and lie alongside. After they have discharged their cargo they will then turn around, having light draught, and return westwards.
The pier layout consists of two breasting dolphins against which the large tankers will berth, four mooring dolphins each pair of which is pro- vided with a fendering system at the back for the berthing of oil barges of up to 1.500 d.w.t. capacity, a central pier (consisting of pipeway and drive- way, intermediate platform and un- loading platform) and catwalks con- necting the pier head to the various dolphins.
The layout of the various structures as finally set out provides the main
DOLPHIN
CATWALK
PIER HEAD UNLOADING PLATFORM
berthing face running in at about 6 degrees to the sea wall. This takes account of the current around the north-east corner of the island which is quite strong, particularly on the ebb tide. All large vessels will be berthed at slack water.
Design criteria
The design criteria for berthing large vessels cannot be arrived at by using the same reasoning as for most structures. In buildings the design loads are seldom exceeded and if they are it is unlikely that the excess will be very great and unable to be ac- commodated without serious over- stressing.
Vessels brought to rest against a pier, however, are a very different problem for the force exerted is pro- portional to the square of the velo- city and therefore whatever velocity is selected for the design it only has to be increased by about 40 per cent. for the applied force to be doubled and by about 75 per cent. for the applied force to be trebled. It is evident that the risk of over-stressing the structure berthed against is fairly high unless an obviously over-designed and expen- sive structure is to be provided.
The problem is to strike a balance between risk and cost. This can only be done by studying the relevant statistics of berthing vessels, deciding upon an economic design life for the structure and hence deducing the cor- responding design berthing velocity
MOORING DOLPHIN
62
45-OMAX.
COMPACTED FILL
EXISTING
13-
QUARRY RUN
'P.D.
ORE MATERIAL
M.H.W.S
M.L.W.S.
FACING
ROCK
SEABED
SECTION OF SEAWALL
DRIVEWAY
INTERMEDIATE
PLATFORM
CATWALK
108
TANK NO. 101
(110) (111)
105
109
106
(107
TANK NO.102
NO.114
D
TANK NO.103
[TANK NO. 104
GENERAL
LAYOUT
S
C
E
100
200
300 FT.
Fig. 1
Far East Architect & Builder April, 1966
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