Our Geotechnical Associate Alex Dent has been involved in the design and implementation of site investigation (SI) for over 20 years. Alex is a founding member of the AGS Geotechnical Working Group, which has recently been looking at the degree of compliance with the geotechnical Eurocode within the ground investigation industry. Given below are some of his personal thoughts on this.
BS EN 1997 ‘Eurocode 7’ (EC7) has been the prevailing British Standard for geotechnical design, including ground investigation, for a number of years now. A recent survey indicated that a significant number of ground investigations do not comply with EC7. The situation is likely to be worst for firms that are not members of trade bodies such as the Association of Geotechnical and Geo-environmental Specialists (AGS).
Whilst it is usual to ensure that designers have an appropriate amount of Professional Indemnity (PI) insurance, works that knowingly fall short of relevant British Standards may not be covered by such insurance.
What can be done to reduce the risk? Firstly it is necessary to consider who scopes the ground investigation. Is it the:
- Project Manager,
- Quantity Surveyor,
- Structural Engineer,
- Civil Engineer?
How conversant are they with EC7 and geotechnical engineering generally? Do they have in-house geotechnical advice they can rely on?
Or is the design of the ground investigation left to the SI contractor? In which case, are they suitably qualified, suitably experienced and sufficiently integrated in to the design to have a good understanding of the development proposals and scope of investigation needed for it? What constraints to budget are they working to – client cost expectations, competitive tendering? Do they have sufficient information on the site? Does the programme allow for sufficient investigation, testing and monitoring?
Poor consideration of these matters at a suitably early stage can be a significant source of ‘below ground risk’ irrespective of the actual ground conditions!
In the event of claim due to ‘unforeseen ground conditions’, without a decent SI how can this be disputed? Who takes design responsibly? Who is the ‘geotechnical designer’? Is it the SI contractor who may have been working to a brief set by another; is it the Engineer? Is it the party who set the SI budget and/or programme?
To manage such risk, a ‘Geotechnical Advisor’ (a suitably qualified and experienced Geotechnical Engineer or Engineering Geologist fully conversant with EC7) should be appointed at an early stage. This Advisor can coordinate the design of the SI, advise a suitable budget and programme, facilitate the procurement of a suitable SI, manage the data and ultimately provide suitable design advice. Such a person should be fully integrated into the design team. Often it is most beneficial if they are an in-house department to the structural or civil engineer as this is likely to result in more joined up and cost effective design solutions for foundations, retaining walls etc.
For most scenarios, EC7 provides explicit guidance on the spacing and depth of investigation points and provides advice on the extent of testing and determination soil properties. Where explicit guidance is not provided (for low risk developments and low rise structures), other standards may be referred to such as BRE 281, 322, 348, 381, 383 and 411, cited in the Building Regulations. However, the status of these is questionable in light of recent events. Where used, they use should be considered in the broader context of EC7 requirements. Additionally, EC7 allows local experience to be used and a number of British Standards have been up dated or reintroduced to be compliant with EC7 (e.g BS5930, BS8004, BS8002 and BS6351).
A further complication is that traditional SI reports do not mesh with EC7 requirements. Traditionally an SI contractor and/or consultant would provide a ‘factual report’ with a separate ‘interpretative report’. EC7 requires a Ground Investigation Report (GIR) and a Geotechnical Design Report (GDR). The GIR is a factual report plus an evaluation of the geotechnical information, including a review of derived soil parameters. The GDR goes beyond the old interpretative report, requiring design advice, design drawings, calculations, specifications and monitoring/testing requirements. More and more geotechnical contractors, such as piling specialists are expecting to be provided with, and contribute to, the GDR. Again a Geotechnical Advisor should be able to guide the reporting process.
If you have any queries concerning managing risk in the ground through the effective design and reporting of ground investigations, please contact Alex Dent.
By Alex Dent, geotechnical associate at CampbellReith.