Environmental Engineering Reference
In-Depth Information
Fig. 5.18 Tugs towing a
oat-out concrete offshore platform
Fig. 5.19 Controlled sinking of a drilling platform by
lling compartments with water
construction to its offshore location. Arranging the tugs in a star formation at the
offshore site enables the substructure to be positioned accurately before being
ballasted with water and lowered to the seabed. Once on the seabed, the substructure
is normally ballasted in its final position with a sand/water mixture. Up until now,
such float-out designs have been constructed primarily for the offshore platforms of
the oil and gas industry. As an example, Figure 5.18 shows a Russian concrete
platform being towed in 2001. The controlled sinking of the platform is shown in
Figure 5.19.
5.4.2.4 Spread and deep foundations
Substructure designs in concrete are generally laid flat on the seabed (spread founda-
tion). Irrespective of the construction and transport methods, the seabed will generally
have to be prepared for such a foundation. This involves either excavating any seabed
soil strata with insufficient bearing capacity or employing soil improvement measures
to upgrade the subsoil. A layer of gravel or other filter material should be laid on the
prepared seabed to provide a stable base and to prevent erosion.
