April_1965 — Page 41

Model Tests Aid Reclamation

THE Kai Tak airport runway, which stretches out into the harbour, did not as had been feared cause the main current in the harbour to speed up, but actually slowed it down slightly.

This was one of the conclusions drawn from a series of model tests carried out by the Hydraulics Re- search Station in England.

A scale model of the harbour was built to guide the Hong Kong Public Works Department in its plans for reclamation works. It was built on a horizontal scale of 11 ft. to the mile and a vertical scale of 1 in. to 5 ft. The seabed was reproduced in accurately moulded cement mortar

and the various piers likely to affect the currents were also constructed to scale.

Tides in the harbour were simulat- ed by two sets of electronically con- trolled wiers, ne at either end of the model. From the test results it was possible to determine what align- ment the various reclamation pro- posals could take without causing adverse effects.

The way in which these tests aided the PWD in its reclamation proposals was explained by Mr. H.R.A. Cham- berlain, acting chief engineer (port works), in a talk given last month to the Hong Kong Rotary Club.

Wanchai Scheme

For example two lines of possible reclamation were tried out for the Wanchai scheme, one starting from the corner of the dockyard and finishing almost below the Yacht Club and the other finishing near the front gate of the club on the causeway.

The tesls showed that neither of these alignments made any signi- ficant adverse effect on the current velocities or flow patterns and so the outer line was chosen as this gave a far greater area of reclamation for almost the same length of seawall,

On the subject of the technique and planning of a reclamation, Mr. Chamberlain said:

"In Hong Kong we are lucky in that development is proceeding at a rapid pace and this involves site formation and the demolition of old buildings both of which require the disposal of material. This means that reclamation in the harbour area is usually a matter of constructing a seawall and then opening the area behind it as a dump. It also means that the cost of reclamation is really the cost of the seawall protect- ing it. Thus when planning

a

TALK

GIVEN

BY

H.R.A. CHAMBERLAIN

reclamation the aim is to produce the maximum area of land with the minimum length of seawall.

"The standard type of seawall construction that has been adopted by PWD consists of dredging a trench in the seabed to remove any soft mud and silt and to get down to a firm bottom. This trench is then backfilled with sand and on top of this a

mound of rubble is then dumped to form a foundation for the actual seawall itself.

"The seawall consists of precast concrete blocks of standard sizes varying in weight from 5 to 18 tons. These are laid on the rubble mound with the aid of divers and built up in layers until they come above the surface of the water. The wall is then completed with mass concrete

UN TO BUILD DAM

UNITED NATIONS are to build and operate a multi-purpose dam at Pa Mong between Vientiane in Laos and Chiengkhan in Thailand.

Dr. Boonrod Binson, secretary- general of the National Energy Council, said recently that soil and other land surveys for the project had been conducted for the past two years. Drilling of rock for building the dam and the purchase of ma- terials and machinery would be car- ried out over the next two years.

The dam will benefit Thailand, Laos, Cambodia and South Vietnam. It will provide hydro-electric power and water for irrigation. The in- stalled capacity will be 1.5 to 2 million kilowatts,

PILING

on

faced with masonry and capped with a concrete coping.

"In order to determine how much of the seabed requires dredging for the seawall foundation preliminary borings are taken by sinking a tube into the seabed until a firm base is reached and the foundation is then designed accordingly. The sand that is put back in the dredged trench being a frictional material is used to spread the load of the rubble and seawall above it evenly over the foundation area.

"There are other techniques for constructing means of protecting re- clamations from the sea such as the use of sheet piling, but it has been found that in Hong Kong in most cases it is still more economical to use the standard seawall.”

Critical Path

Mr. Chamberlain said that in the planning of the Wanchai project Critical Path Methods had been used.

By this method it had been pos- sible to determine such things as the order that the work must be done in and the activities which were critical from the timing point of view. It was possible to determine in the event of a delay in any part of the job what effect if any this would have on the completion date of the overall project.

By using this modern technique it was hoped that the problems and difficulties experienced in the past would be minimised in future schemes.

there had been some delay in starting the work because of difficulties faced by the Government in acquiring land at the sites from the owners.

The Public Works Department has started dumping earth on the swamplands to build approach roads to the two bridges.

The Muar bridge will have a span of 1,200ft. and the Batu Pahat bridge will be 900 ft. long. Each will be able to carry

a maximunt load of 150 tons. When completed, the two bridges will replace the existing ferries.

HARBOUR CONTRACT

A MAJOR civil engineering contract for dock improvements for the Bombay Port Trust has been awarded to a Consortium headed by Kier Ltd., JOHORE BRIDGES

London, and including Sentab Ltd., work has started

of Sweden the

and The Engineering foundation of bridges over the Muar

Construction Corporation of Bom- and Batu Pahat Rivers in Johore. bay.

The two bridges, on the north- south coastal trunk road, are due to be completed by November next year.

A spokesman of Development Services Ltd., one of the two firms which have been jointly granted the M$5,2 million a

contract, said that

Far East Architect & Builder April, 1965

The project, which is valued at approximately £8 million, is due for completion in four years, and was awarded in open international com- petition.

The consulting engineers for the scheme are Bertlin and Wilton and Bell of London.

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