Support Methods

From the foundation point of view, these platforms can be divided into two major categories (Werno et al., 1987)  

Mat type, with three or more legs supported by a common mat. 

which generally cover the total area of the platform, are usually A-shaped. The thickness is about 3 m. The performance of mat-supported rigs has been described by Hirst et al. (1976), and by Young et al. (1981). They have the disadvantages that they require a relatively level bottom and that they are affected by differential settlements caused by eccentric or cyclic loading and by scour. However, the advantage is that a mat foundation can be used in very soft soil because of the large surface area. 

Configuration of spud cans. (After Werno, M. et al.. Marine Geotech., 1, 65-78,1987. Reprinted with permission from Marine Geotechnology, Vol. 7, No. 2, Copyright Taylor Francis Group.) 

Piles can be used where there is a layer with a high bearing capacity close to the bottom. Very long piles will be required when the depth to the bearing layer is large. 

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