The laying of the crushed stone on the foundation course, the most im- portant and difficult part of the pro- ject, has to be finished precisely and efficiently.
Bird's eye view of construction site at the mouth of Tama River
and are reinforced with concrete at a dock provided near the construction site. They are then transported by catamaran placing barge to the placing location. Before submersion they are overlaid with crushed stone of about 200 tons underwater weight so that they will sink.
Two tube elements are connected by automatic couplers (See Fig. 3-6). Two couplers are provided to both sides of the tube elements, the first being firmly pressed against the gasket gum packing of the second. When the two elements are connected, the scup- per valve at the bulkhead of the first elements opens to discharge water in between the bulkheads of the two elements. With the discharge of water the elements are completely connected by external water pressure, which in the Tama River is 1,200 tons.
After the discharge of water the bulkheads of both tube elements are removed, the elements are welded to- gether and the joint reinforced with concrete. Sand and crushed stone are placed around the tube and, to give stability, mortar is grouted between the tube and the foundation course through grouting pipes provided on the tube bed.
A screed machine resembling an underwater finisher has been developed for the work.
The machine supplies crushed stone from the surface through tele- scopic pipes to its underwater stock pile, which travels on both sides of the excavated trench on chained rails which prevents the piles from slipping. The crushed stone is evenly placed on the foundation course by the stock pile.
The placing-barge for the Tama River project, a 300-ton, 60-metre long and 32 metre-wide catamaran- type floating crane, was specially built for the purpose. It is equipped with winches for mooring, fine movement and lifting. It has an electrical equip- ment room, a control room and ballast tanks. Winches and crane are remotely operated by one-man control from the control room.
In underwater operations in dark- ness as on the Tama River, frogmen are used only for high precision work such as installation, removal and in-
spection of machines. All tunnel con- struction is done from the surface by machines.
Construction of the Tama River underwater tunnel was started in De- cember, 1967 and is expected to be completed in September of 1970. Hong Kong tunnel
The mile-long submerged tube tun- nel being constructed across Hong Kong harbour will be the longest of its type in Asia.
It will carry two 22 ft. carriage- ways. Each tunnel section will consist of twin tubes, 34 ft. in diameter and about 350 ft. long, constructed of steel shell with a reinforced concrete lining.
The joint consulting engineers to the tunnel company are Scott, Wilson Kirkpatrick & Partners and Freeman, Fox & Partners. In addition, Parsons, Brinckerhoff, Quade & Douglas, of USA, are advising the contractors on the design of the immersed tube. Robert Mathew, Johnson-Marshall are assisting the joint consulting engineers with architectural services on the pro- ject.
The contractors are Costain Inter- national Ltd.
Far East BUILDER, December 1969
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