WORKING GROUP 9 
CHIN FUNG KEE 
495 
The mantle of lateritie soil which covers the greater part of the surface of the 
country is of a cohesive nature. The failure of slopes and banks is characteristic 
ally preceded by the formation of tension cracks behind the upper edges of the 
banks. The depth and size of these cracks are further increased by shrinkage in 
the dry period. These cracks form natural channels through which water can 
rapidly penetrate and saturate the soil to cause failure by increasing the bulk 
density and reducing the shear strength and cohesion of the soil. 
Malaya has well defined wet and dry seasons and even during the monsoons 
long dry spells may separate wet periods, when torrential rainfalls of four 
inches in a day are not uncommon. Landslides, therefore, tend to occur at the 
beginning of a rainy season which follows a particularly dry spell. 
Even on a scale of 1 : 5,000, and on surfaces free from undergrowth and 
“blukar”, the tension cracks of potential landslides are imperceptible. But 
large slips are invariably associated with the indiscriminate clearing and re 
moval of the protective mantle of vegetation, and in certain cases the surcharg 
ing of the natural banks and the increase of the steepness of the slopes with the 
dumping of soil. The exposed lateritie soil, however, stands out distinctly in 
light tones different from the virgin vegetation of the adjacent undisturbed and 
stable land, providing an amazing contrast when viewed stereoscopically. 
Fig. 1. Potential landslide 
The manifestations perceptible from the photograph are: 
1. the difference in tone between the bare slope and the darker background of the adjacent 
stable slopes which are covered by protective vegetation; 
2. the presence of slip material on the opposite bank of the stream resulting from soil flow; 
3. the bank is subject to undercutting by the stream; 
4. the steep slopes. 
5. the erosion gully system.