Alternative Anchor Options
In addition to the uplift resisting anchors described in the previous sub-section, a number of alternative options are also available:
"Anchors in the form of grouted in bars, tubes or cables are the most economical means of providing the required uplift resistance for piles taken down to a shallow rock layer." (Tomlinson, 1980)
Piled Foundations
High capacity load resisting foundations may be required to withstand large uplifting forces imposed upon the anchorage. For foundations of marine structures preformed or partially preformed piles lend themselves to ease of installation. Piles are driven to the design depth using a percussion hammer and grouted into position. They are suitable for use in very stiff, compacted clays and in rock. A tubular steel pile with a cutting edge is driven and down-hole equipment will ream and remove the rock surface until the required depth is achieved. Piling operations in the marine environment are very expensive and logistically difficult. While it may be necessary to utilise piling in certain circumstances, for the purposes of this design piling would only be considered as a last resort due to the prohibitive costs involved.Suction Caissons (Piles)
These can be deployed on a large or small scale (suction anchor). At the larger end of the scale they are essentially a pile with the top end sealed. Once pushed into the seafloor an internal vacuum is created using suction until the desired holding capacity is achieved. Again, these are expensive to construct and install.Vertical Load Anchors (VLA)
Vertical load anchors are a relatively modern development coming to the offshore industry in the last fifteen years or so. As the title suggests VLAs can resist vertical load and horizontal loads, while conventional drag embedment anchors are for horizontal loading applications only.