Pile Design and Construction Practice, Fifth edition

508 Ground investigations, contracts and pile testing
11.1.5 Offshore investigations
Offshore investigations for deep-water structures and oil production platforms are highly
specialized and, although the basic procedures contained in the British Standards and
Eurocodes for geotechnical investigations should be adhered to for UK waters, there are
many additional Statutes and Regulations which apply to such work and are outside the
scope of this text. Draft Guidance Notes on Site Investigations (11.15) have been prepared by
the Society for Underwater Technology to provide a basic framework for offshore investigations,
particularly for renewable energy projects, citing practices and regulations for
the UK, other European regulatory bodies and under API regulations. Foundation design
considerations include driven piles, driven and drilled piles, suction piles, and gravity bases.
11.2 Piling contracts and specifications
11.2.1 Contract procedure
In Britain it is the usual practice for the piling works for foundations on land to be executed
as a sub-contract to the main general contract. Foundation piling rarely forms a high
proportion of the total cost of a project on land, and the administrative arrangements and
preliminary works required for carrying out the piling as a separate advance contract are
unjustified in most cases. Works which are required in advance of a piling contract include
such items as demolition, fencing, levelling and grading, the construction of site roads,
the erection of site offices, and the supply of electrical power and water. On some large
contracts it is the practice to let a separate contract for these advance works, in which case
it may be feasible also to let a separate contract for the piled foundations. Piling contractors
prefer to do the work in this way rather than as sub-contractors. The responsibilities of each
party are defined more clearly and, from the piling contractor’s point of view, a directly
employed contractor has the advantage that he is paid retention money after the usual period
following the completion of his work. Where a piling contractor works as a sub-contractor
it is usual for part of his retention money to be withheld until the main contractor’s retention
is released, which may be several years after the completion of the piling work.
Piling normally forms a high proportion of the cost of marine construction and it is
usually undertaken directly by the main contractor. Any sub-contracting is limited to
specialist services such as grouting or the construction of anchorages to tension piles, and
to the supply of prefabricated components.
Piling carried out as sub-contract work may be done by a nominated contractor, i.e. a
specialist piling contractor, who has submitted a tender to the Employer/Engineer in advance
of the main contract and is then selected for nomination in the main contract documents.
Alternatively, the main contractor can, after appointment, invite tenders from selected
specialist contractors, or from an open tender list, to be employed as sub-contractor.
The Civil Engineering Contractors Association has prepared a form of sub-contract (the
CECA ‘Blue Form’) which can be used with the addition of a suitable clause to cover piling
work. On building contracts under the control of an architect, the contract conditions are set
out in the Standard Forms of Building Contract prepared by the Joint Contracts Tribunal
(the ‘JCT’ forms), with various provisions for ‘domestic’ and nominated sub-contractors. In a
similar manner the National Federation of Building Trades Employers has prepared standard
forms of contract for nominated or non-nominated sub-contractors. In addition, ad hoc and
bespoke forms of sub-contract prepared by main contractors are increasingly used to change
the liabilities and risk-sharing obligations given in standard forms. Collateral warranties,