CRACKING WALLS IN NEW BUILDINGS
THE phenomenon of cracking ceil-
ings and walls in newly-con- structed buildings was, until recently, accepted as a simple, natural settling which occurred during the infancy of a building.
However, when a heaving of the foundations of new houses in parts of the Orange Free State, an area southeast of Johannesburg, South Africa, was reported. the observed levels were at first disbelieved.
The first person to focus the spot. light on the cause was an engineer at the University of the Witwater- srand. johannesburg. The theore- tical research of Dr. K. Knight, a member of the Department of Civil Engineering, in conjunction with the National Building Research Institute, not only explains the observed effect but offers a means of predicting its
occurrence.
Dr. Knight's research started with measurements which revealed that the level of a house can not only go down by compressing the soil founda- tion, but amazingly, it can go up as
well. This happens in clay soil areas where evaporation exceeds precipita- tion. When an area of ground is covered by a building, evaporation is prevented, the clay swells, and the house goes up, with resulting crack- ing.
Dr. Knight resolved to analyze the stresses caused by heaving and to put them into equation form in order to predict the effects and avoid future losses, which can run into millions of dollars. The large number of
variables involved, e.g., precipitation, permeability, evaporation, tempera- ture, etc.. made the task impossible to perform manually. In 1962, an IBM 1620 computer installed at Wits University lent itself naturally to the task. A mathematical model of heave was built, and is now being augment- ed by the introduction of actual physical parameters such per- meability, temperature, etc., in order to simulate heave conditions any- where in the world.
ESTATE AT CHEUNG SHA WAN
new resettlement estate with four annex schools, estimated to cost more than HK$32 million, is to be built on land is now being reclaimed from the sea at Cheung Sha Wan Bay, Hong Kong.
Site formation and piling work for the new estate, which will accom- modate about 41,000 people, is ex- pected to start in September this year if the reclamation is completed by then. Actual construction work will
as
begin about two months later.
The entire project is expected to take about 2 years to complete.
The new estate will comprise two connected eight-storey blocks and a series of nine 15-storey blocks of the standard central corridor type, inter- connected at suitable points to form a pleasant layout with ample open space, children's playground, parking space, service area and market space in between.
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THE HONG KONG & FAR EAST BUILDER-VOLUME 18, NUMBER 6
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