Hong Kong Builder
31
A.R.P. TUNNELS
IN
HONG KONG
Completed section of tunnel lined with rubble walls, concreted floor and T-beam roof.
Fublic air raid shelters of deep tunnel type, such as are being constructed by Marsman Hongkong China Ltd. for the Government of Hong Kong, are designed to pro- vide full protection against heavy bombs throughout their full length except for the short lengths immediately
An intermediate stage in lining the tunnels. Wood shoring just about ready to be taken away.
adjoining the portals where sufficient cover is not obtain- able.
The peculiar geological and topographical feature of Hong Kong together with the material to be obtained locally were governing factors in deciding the type of
tunnel to be adopted. Standard sets of heavy squared timber with timbered lagging to sides and roof in accordance with recognised mining practice were used. With this method and with the aid of compressor plant and mechanical ap- pliances it was possible to make the maximum progress in the development of the respective sites. On completion of the layout a progressive programme of replacement of the timber by a permanent form of lining is undertaken (see photographs). This is being economically car- ried out by utilising the stone taken out of the tunnels driven in rock and the timber removed is reused in driving new headings. The per- manent lining not only increases the strength of the shelter but assists drainage and ventila- tion and increases the cross sectional area and consequently the accommodation.
The type of precast arch beams being used for the tunnel roof was decided upon only after extensive tests on a number of different designs