FOUNDATION TESTING IN HONG KONG
By R. D. Russell of Geo. Wimpey & Co., Ltd.
A sample has just been brought to the surface. "A" Culting Shoe. "B" Sample Tube, "C" Sliding Hammer.
It is a customary practice these days to learn as much as possible of the ground on which it is intended to build before any foundation work commences.
In the past, the failure of many buildings has been due to a lack of knowledge of the ground underneath and of the stresses set up by heavy foundations and also of the effect of water percolation on the settlement of structures.
It was. moreover, impossible to determine accurately the bearing capacity of the soil at any great depth. The method of piling was to drive more or less to refusal, so that the length of the pile could not be calculated beforehand nor the cost estimated.
It has been proved that, by knowing exactly the various strata of the ground, the cost of the foundation is lessened in that the exact type of foundation can be determined and there is thus no wastage of labour or -materials. Moreover, it is possible that, in driving piles without any knowledge of the strata through which they pass, the water content of the subsoil may be changed and settlement may occur. For these reasons, boreholes have been sunk on the site of the new Bank of China Building.
The operation consists of, firstly, excavation through the topsoil, fill, etc., which in this case involves a pit some 12′0′′ deep, and secondly of erecting the tripod and inserting the
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first length of outer casing which carries the cutting shoe and which is 4" internal diameter.
Into this is inserted the auger which also carries a cutting shoe and to which is attached the first length of rod. The whole is then driven into the earth and further lengths are connected and driven down.
At every five feet, or at any pre-determined depth, the auger and rods are withdrawn and a sample is taken in a 3′′ X 20′′ sample tube which has a cutting edge attached and is driven down by means of a sliding hammer to the required depth. It is then withdrawn and sealed so as to retain the moisture content of the sample which is sub- sequently dispatched to the laboratory for analysis and for consolidation and shear tests.
The 4" borehole is continued until it is considered bed- rock is close and then the diamond drill is brought into use. This consists again of a series of rods to which are fixed a diamond studded bit and a core barrel, which are inserted through the outer casing and driven by a small gas engine. During drilling water is pumped down to cool the bit and to wash away the fine cuttings.
It is usual to empty the core barrel every 10′0′′ or so in order that no likelihood should exist of mistaking an isolated boulder for bedrock.
By courtesy of Messrs, Palmer & Turner, George Wimpey & Company are now engaged in sinking trial boreholes on the site of the proposed building which is to replace the Alexandra Building, and the photographs are of the operations on this site.
The drilling work in Hong Kong is in charge of Mr. J. Gibson who has had extensive diamond drilling experience in Canada, the United States and Great Britain.
(Left) Casing Shoe showing the diamonds inset round the cutting edge and (Right) Core Bit showing the diamond studded cutting surface,
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Up to recent years aluminium products, particularly flat and corrugated sheeting for external sheathing of buildings, did not enjoy a large sale in Hong Kong. The reasons were probably in its comparatively high cost, difficulty of obtaining materials when required, and Hong Kong's well-known resistance to the employment of materials about which they know little.
Our attention has been called to aluminium sheets manu- factured by the British Aluminium Company Limited which are being marketed under the trade name of "Rigidal" which the manufacturers claim to be the ideal corrugated metal for general building purposes. They claim that under the most severe industrial atmospheres in England and under extreme climatic conditions in the tropics, aluminium has demonstrated its remarkable qualities of endurance in comparison with other building materials. In addition to durability, its tightness of weight reduces costs because it makes handling and erection easier. It is easy to maintain since paint is not necessary and repair and maintenance costs are practically negligible. The high reflectivity of the metal improves light efficiency inside the buildings, and its clearness of appearance and free- dom from rust ensures a constantly attractive appearance.
Probably the main important advantage is its thermal efficiency due to aluminium's high reflectivity and emissivity. The graph printed below illustrates clearly this property.
The economies in the use of this material mentioned above more than offsets its slight additional cost over competitive materials, and makes it, in the long run, far cheaper to use and far more satisfactory for the many purposes for which it is employed.
A. R. Burkhill and Co. Ltd. of 702 Marina House, Hong Kong, are the sole agents for "Rigidal" for Hong Kong and China. They issue a very attractive, well illustrated booklet giving full information and useful data оп the use of aluminium sheets.
The illustrations on the left show graphically the result of tests carried out in Calcutta to compare the insulating values of three methods of sheathing buildings:
(Top) Corrugated galvanized iron single skin house. (Centre) Corrugated aluminium sheet single skin house. (Bottom) Corrugated aluminium sheet double skin house.
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