58
Fig. 2.6: Liner shutter in position in 30 ft. equivalent diameter tunnel
throughout most of its length with 10 in. of concrete. The subsidiary tunnels were lined with sprayed con- crete where bad rock was encounter- ed, but elsewhere left unlined except for the invert which was normally 6 in, or 9 in. thick.
The figures given in the table do not include portals or surface works,
centralised
expenses or overheads. They therefore relate, roughly speak- ing, to work carried out and costs incurred underground only.
Conclusion
This is probably the first tunnelling contract in Hong Kong to be carried
out substantially by contractor's direct labour as opposed to subcon- tract labour. It is also noteworthy for a relatively high investment in plant, in qualified engineers and for the utilisation of the most up to date development in tunnelling techniques.
All these are factors which pro- duce high overheads but this money can be recovered by having a high standard of pre-planning and works organisation. Tunnelling is a repeti- tive, mass-production job which re- sponds well to such treatment and it is the author's opinion that in any large tunnel works the costs are minimised by this type of approach.
No amount of pre-planning and detailed organisation can bear fruit if all aspects of the work are not equal- ly subject to rigid centalised control and, for this reason, the sub-contract system is not appropriate to tun- nelling on this scale. It is of no overall benefit to the job if excavation is carried out at minimum cost but finishes late and valuable concreting plant is kept waiting, or huge sums have to be expended filling with con- crete the over-break left by an ex- cavation sub-contractor who was careless in blasting.
It has been established that local labour can be economically employ- ed without the interposition of sub- contractors and that, where close control and co-operation are neces- sary, this leads to an increase in overall efficiency.
NAN
Metal Casement Fittings
S.F. WONG, Box 1232, Hong Kong
Agents: N.P. KING, Box 79, Singapore
SMITH WALLIS & CO. LIMITED Highgate Road Birmingham 12: England
Far East Architect & Builder December, 1967