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Hong Kong Builder
Further stages in the completion
of the tunnels.
Left:
Arch beams being set in place between sections of tim- ber shoring.
Below: The first stage in lining the funnels. The timber wall lagging is being replaced by rubble stone walls.
had been carried out. These designs included various shapes of T-beams and arches and the type finally chosen represents the most satisfactory combination of strength and economy.
The number of entrances are laid off to conform with recommendations of the A. R. P. Department in England and will permit of 800 people passing through each portal in four minutes. The portal entrances will be protected by blast curtains formed by concrete blocks.
The tunnels are so located that they provide shelter for the greatest number of people in the shortest possible
time. At the same time geological and topograhical fea- tures have to be considered and tunnels are placed in such a way as to obtain the full benefit of such features.
Adequate drainage is provided by means of precast channels sunk in the concrete floor. The floor is laid on dry core which enables the subsoil water to percolate to the channels.
Natural ventilation will be assisted by artificial means. The various forms this will take is dependent upon the natural conditions met with and the extent of the system of tunnels under consideration. Tests so far
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