the lower levels of this formation, often the removal of the hills for de- velopment has brought this level near the surface: it would seem reasonable that spread foundations might pro- vide suitable foundations for high buildings after making careful inves- tigation. Tests indicate that the com- pact decomposed granite has low compressibility and low permeability. The thickness of the formation would be an important factor to be taken into account.
In Hong Kong a particular pro- blem is the presence of large boulders overlying the bedrock when the en- gineering need for founding to rock is essential. Generally, where bed- rock exists at considerable depth, the only economic method is by sinking cylinders, of which the bored type from the surface has come into the fore in recent times. However, the presence of these boulders makes boring within steel tubes difficult and usually impossible and resort has to be made to other methods for sink- ing the cylinders. Brief mention has been made to the employment of drilling mud, and it is fortunate that there has been considerable experi- ence in the use of this medium in order to provide large diameter bored cylinders to carry heavy loads from structures like high buildings in con- ditions which are very much the same in principle as those that exist in Hong Kong.
Such boring techniques are general-
ly to be preferred to the alternative of sinking cylinders by hand and the methods have been successfully used in various parts of the world. When the excavation is carried out by hand below the water table and in fine grained soils particularly, there are the same inherent problems as for normal deep excavations, that is, the dangers of piping and the loss of ground affecting the adjoining struc- tures, neither of which arise with the reverse circulation method using special drilling muds.
com-
Under certain conditions, pressed air can be used to sink cylin- ders, but this is usually very expensive and there are limitations of pressure in which men can work.
Codes of Practice (5, 6) give some guide to the architect and engineer, while local Building Regulations re- quire to be kept under constant re- view to ensure that they conform with current practice and do not provide an excuse for work to be carried out at the minimum standards.
Conclusions
Remedial measures that have had to be taken from time to time on foundations which have been unsatis- factorily designed and constructed nearly always arise due to one or two of the simple points that have been mentioned in this paper being over- looked or some significant point not being checked.
It is not reasonable to put all the blame on the ground today for a foundation failure as there are SO many facilities at the disposal of the architect and engineer to employ to make sure that he has taken every reasonable care in his design.
The future of high buildings in Hong Kong will depend on the com- petence that architects, engineers and contractors working together as a team can give to investors in site de- velopment.
References
1.
2.
3.
4.
5.
6.
Ruxton, B.P. (1960) "The Geo- logy of Hong Kong", part 3, Vol. CXV, Geol. Soc. London.
Davis, S.G. (1952) "The Geology of Hong Kong", Government Printer, Hong Kong.
Ruxton, B.P. & Berry, L. (1957) "Weathering of Granite & Asso- ciated Erosional Features in Hong Kong", Vol. 68, Geol. Soc. America.
Skempton, A.W. (1955) "Foun- dations for High Buildings”, Proc. Instn. Civ. Engrs.. part 3, Vol. IV, London.
British Standard Code of Prac- tice CP2001 (1957), “Site Inves- tigations". British Standards Institution, London.
British Standard Code of Prac- tice No. 4 (1954), “Founda- tions". British Standards Institu- tion, London.
SEALING, CAULKING, GLAZING with
SYNTHETIC RUBBER BASED.
BUTYL RUBBER
Biddle's CAULKS
POLYSULFIDE
......
Thiskol SEALANT & PUTTY
See the revolutionary advancement achieved by years of scientific research... Weld-like lasting chemical bonding up to every job. Absolutely water-tight and maintenance-free. One-shot, ready for use. Five year guarantee and - VERY ECONOMICAL!!!
Call now HONG KONG ALUMINIUM LTD. Tel. 233073-5
505 FU HOUSE, 7 ICE HOUSE STREET, HONG KONG
Far East Architect & Builder September, 1965
63