up to 2000 pounds have been reported utilizing this technique. More 

 detailed information on capacities, techniques, and equipment is available 

 in Reference 20. Attention must be paid to prevention of corrosion, 

 particularly in typically highly stressed rock bolts. 



Foundation Materials 



For structures in this category it is generally recommended that 

 unusual materials be avoided and that standard structural steel, 

 aluminum (Type 5086), concrete, or plastic (Polyvinylchloride - PVC) 

 be used. Oversized members, from a stress analysis design standpoint, 

 and large rigid connections are suggested. Where it is necessary to 

 have a flexible joint, it should be encased in a flexible jacket and 

 the jacket filled with oil and sealed. Many such joints requiring 

 flexibility for only a short period of time may not require oil-filled 

 jackets. For example, flexibility may be required only until the 

 foundation is resting on the seafloor and the flexible joints have 

 allowed individual footings to adjust to the local irregular topography. 

 For this case, exposed flexible joints may be used, by the time 

 corrosion or fouling locks up the joint, all required movement will 

 have been completed. 



A foundation made of standard structural steel with welded connections 

 is a practical solution. Where additional weight is needed in the 

 foundation, in order to resist lateral forces, concrete can be added. 

 A dense, high-strength concrete, mixed from sulfate-resisting cement 

 and sound aggregate is most reliable. The concrete should provide three 

 inches of cover over any reinforcing used in order to minimize corrosion. 

 Where weight must be reduced or minimized, a welded aluminum or plastic 

 foundation is suggested. PVC plastic has very low weight in water and 

 offers yield strengths at> high as 9,000 pounds per square inch. It is 

 however more expensive than aluminum. 



Both steel and aluminum (Type 5086 only) are recommended because 

 both have fairly uniform rates of corrosion. Protective coatings can 

 be used; however, these are typically scratched during routine handling 

 and deployment. Any scratched area will be subject to local accelerated 

 corrosion. In general, it is recommended that oversized sections 

 (thicknesses increased by 1/4 to 1/2 inch over what is required by the 

 stress analysis) be used, and corrosion be allowed. Cathodic protection 

 is helpful, but it must be properly designed. Contact of dissimilar 

 metals cannot be allowed, except in the case of sacrificial anodes. 

 If such connections are otherwise necessary, the two materials must 

 be isolated from each other with plastics or similar materials. Corrosion 

 rates for metals in direct contact with the seafloor are often accelerated 

 by a factor of two or three. 



In some design situations, it may be necessary to reduce the in- 

 water weight of an installation below what is possible by careful 

 selection of materials. For these cases, buoyancy can be added. In 



13 



