I can’t believe they invented it: “factual” vs “interpretative” geotechnical report

One of the things I’d like the most about my job is the fact that I still learn new things, even on topic were I wrongly believe there is not much more new to see.

This week during a telco with my accomplice in crime Eduardo I’ve discovered a new trick that I suspect has been invented by someone in the US (or possibly in the UK) – the split between “factual” and “interpretative” geotechnical report.

In the countries were I’ve worked until today, the geotechnical survey is usually a huge package of documents full of formulas, picture, diagrams and numbers. I’ve been never touched by the idea that part of the content was somehow different.

However, I’ve discovered that somebody (I bet a lawyer) introduced this categorization.

The Geotechnical Data Report (AKA the “Factual stuff”) would be the part including things like:

  • Pictures
  • Boring logs
  • Trial pits logs
  • Field test (SPT, cone penetration, etc.)
  • Laboratory data (water test, CBR, etc.)

This is the type of things that could safely land in a contract and that should be shared and used by the subcontractor.

However, a civil engineer would like to see other information to do his work. He would expect the type of information that should appear in the Geotechnical Interpretative Report (AKA the “don’t rely on me stuff”), with things like:

  • Ground behaviour of geotechnical units
  • Slope stability
  • Seismicity
  • Geotechnical cross sections
  • Construction methods and proposed technical solutions

Basically, nothing connected with design and construction.

Know you know that, wherever possible, you should ask to the geotechnical survey company for the full package (factual + interpretative) but keep them separate – at least if you face a big project with a high geotechnical risk.

Said that, I also want to reiterate my opinion that a good geotechnical survey can make the difference between a successful project (at least for roads and foundations) and a nightmare project with claims and over cost.

It might be difficult to find the budget for this kind of investigation in the early phases of the project but believe me, it’s worth every euro that you will spend on it.

2 responses to “I can’t believe they invented it: “factual” vs “interpretative” geotechnical report”

  1. Simon Avatar

    Nothing new or unusual in this approach … certainly in Europe where it is in full accordance with Eurocodes and EC7. EC7 identifies two reports (which may of course be combined, or as one document, but the content is very different as you note). GIR – Ground Investigation Report (your ‘factual report’, but actually Factual+ as it has to assess results and provide characteristic values, data plots etc., which some GI contractors (used to traditional Factual Reports) do not like!). And the GDR – Geotechnical Design Report (your ‘interpretative report’) that takes the factual info from the lab and in-situ testing and uses the data to obtain derived values/parameters that are then used in design with the appropriate partial factors (e.g. of the foundations, assessing the bearing pressures/capacity, the piles or ground treatment, checking rotational stiffness etc.). This is where the consultant comes in and earns his money / puts the PI on the line.

  2. Muhammad Asif Khan Avatar
    Muhammad Asif Khan

    Very useful Article, we do the same here in Saudi Arabia, we prepare 2 separate reports (a factual report & a draft report) as u mentioned, we take great care while writing the report that we are not responsible for any structural behaviors or natural settlements or variations of grounds.

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