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Technical policy relating to foundations and geotechnics for offshore installations in the UK continental shelf (UKCS)

Document development – QA sheet

Purpose of issue Rev Date of issue Technical author Policy contributions Technical editor
Comment 0 Nov 07 R Martland   R Martland
Comment by Team Leader 1 Jan 08 R Martland None M Birkinshaw
Issued 2 Jun 08 R Martland None M Birkinshaw

OSD technical policy for foundations and geotechnics for offshore installations in the UKCS

Technical policy

Dutyholders should be able to demonstrate that;

It should be noted that, although the above relates primarily to foundation assessment processes, the ultimate objective is to ensure a suitable failure probability for the global structural system is maintained throughout the life-cycle of the installation, taking into account the total risks to personnel on the installation.

The technical issues are complex and more information is available in HSE Research Report RR676 Review of Technical Issues relating to Foundations and Geothechnics for Installations in the UKCS[1]

Impact of this policy

The standard set by this policy is compatible with the International Standards Series for Offshore Structures (specifically BS EN ISO 19901-3: 2001 Petroleum and natural gas industries. Geotechnical and foundation design considerations) and there should be no adverse impact on new installations designed to the new standard, nor on existing structures using the processes and procedures described in this standard.

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Nature of threat

Foundation integrity is probably the most vital aspect of structural integrity as in most cases the loss of any one individual foundation support (e.g. pile, or spud-can) will either lead to global structural failure, or the requirement to abandon the installation, both of which could lead to multiple fatalities and injuries. The integrity of the foundation system requires therefore a sufficient collection of soil data via site investigation, the interpretation of this data for design and the adoption of reliable design practices.  It is clear therefore that foundation integrity is critical to the safety of individuals on the installation and requires detailed evaluation involving appropriate competencies such as geotechnical specialists, of limited data, collected from variable material (soil).

Risk level

There are no precise methods to quantify risk and sound engineering principles are required to keep this risk to a low level. Managing the risk by use of techniques and methods in the ISO Standards for Offshore Structures (specifically BS EN ISO 19901-3: 2001 Petroleum and natural gas industries. Geotechnical and foundation design considerations) is used to ensure that no sudden, catastrophic failure is encountered.

Accident history and foreseeability

There have also been several cases on the UKCS of jack-up leg damage (brace snapping) during installation that has been related to problems associated with re-entering existing footprints and eccentric loads on the footings. Worldwide there have been numerous failures to both fixed installations (particularly in the Gulf of Mexico hurricanes) and to jack-up installations during both initial set-up and operation that have led to complete failure of the jack-up installation. In some non UK cases jack-up foundation failure has caused the jack-up to collapse onto fixed installations, causing release of hydrocarbons leading to major fires and loss of life from both installations that have been working in combined operations.

There are no known instances of offshore pile failure on the UKCS, although degradation and deterioration of piles (ageing issues) are mainly uninspectable and hence inherent safety, based on sound, good practice is paramount. 

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Worldwide practice

The level of integrity has traditionally been set through prescribed Regulation in the North Sea, by an industry standard (API) for the USA, and Class Rules.   These practices, for foundations, have been harmonized through ISO to a set of appropriate criteria, similar to those in place in Norway. This Technical Policy is based on the ISO criteria.

Background

The design assessment practices for foundation systems, such as pile and jack-up shallow raft footings, have been subject to significant improvements over the period from the early 1960’s during the Southern North Sea (SNS) development, through to the later field developments in the deeper waters of the Northern North Sea and West of Shetland. These improvements have been gained by a sustained research programme by industry and HSE. The type of loading experienced on certain lighter topside installations in the Central North Sea has also created high cyclic load ranges which have the potential to reduce the capacity of the pile foundation systems during storm conditions. The practices for site investigation have improved significantly leading to better quality evaluation of the capacity of foundation systems, but there are still many design practices currently employed in the offshore arena that do not offer a consistent, or robust, integrity level for certain installation and foundation types.

The current practice for offshore foundation design and re-assessment is contained in the following standards:

All structure types

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Fixed structures

Jack-ups

Relevant legal requirements

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Remedial actions

Remedial actions will depend on the degree of lack of conformance with the relevant Standard or original design intent. However, of utmost importance, is for the nature of the non-compliance with best practice to be evaluated in a systematic way. This should take into account the degree of loss of integrity based on a best practice foundation re-assessment, taken together with a well-informed structural and foundation integrity management system.

Remedial actions may take the form of:

It is expected that due consideration will be given in design and operation to a series of factors that could impact on the integrity of the foundations systems adopted.

Pertinent technical issues and detailed guidance

The impact of Technical Policy will likely involve a demonstration involving a combination of the following aspects;

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Key issues in initial design and installation

Factors that may require particular attention include:

Pile design and analysis is currently undergoing an important stage of technical development, with new methodologies and recommendations coming into practice.

Guidance on technical issues and best practice on the critical design issues and topics that may need to be addressed in both site investigation and re analysis is published  in HSE Research Report RR676 Review of Technical Issues relating to Foundations and Geotechnics for Offshore Installations in the UKCS.

Consideration will also given to possible monitoring and strengthening of foundations systems. The Report will also provide lists of relevant publications and useful references to background material and guidance on specific topics.

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Updated 2012-12-13