1. GBRs - Ground models you can just make up ?
John Davis
Geotechnical Consulting Group

2. What is a Geotechnical Baseline Report (GBR) ?
Why don’t GBRs have to be true ?
Where & why is a GBR used ?
How does a GBR work ?
Why give this presentation ?

3. What is a GBR ? A GBR is a purely commercial document.
It aims to set out an unambiguous and measurable Ground Model which determines the allocation of contractual ‘in ground’ risk between the Employer and the Contractor.
It is different to a conventional Ground Model in that it doesn’t always have to be ‘true’ or reasonably based on evidence.
and it must be measurable in a construction setting

4. What is a GBR ?
A GBR sets risk boundaries by including statements (Baseline Statements) that define the relevant geological or geotechnical conditions that the contractor can expect to find during construction.
If conditions are found to be equal to or better than a Baseline the contract value is unaltered.
If conditions are found to be worse than a baseline and the contractor can demonstrate a loss, a compensation event is triggered.

5. What is a GBR ?
At tender the GBR is used by all tenderers as a common basis for pricing geological and geotechnical risk. At award the contractor is deemed to have allowed for the GBR ground model in his tender.
Post contract award the GBR is used to judge the validity of any ground based compensation event claims for those issues covered by the GBR.
The Baseline Statements establish what is ‘foreseen’ & ‘unforeseen’ by the contract in relation to the ground conditions encountered during construction.
If well written GBRs can provide an efficient means of dealing with claims.

6. Why don’t GBRs have to be true ?
GBRs are commonly written by Clients and imposed on tenderers through the tender process.
This gives Clients the ability to accept ground risk (lower price / less price certainty ?)
Or to transfer it to the Tenderers (higher price / greater price certainty ?)
Different Clients have different appetites for risk and different abilities to bear risk.
“It’s a gamble either way”

7. Why don’t GBRs have to be true ?
Risk boundaries in Baseline Statements can be moved from their ‘true’ positions by adjusting them so they are less ‘true’ or less ‘reasonable and realistic’.
Additionally the requirement that all Baselines are ‘unambiguous and measurable’ sometimes means Statements have to be ‘made up’.
Sometimes Clients like to ‘buy’ some certainty for high risk but unknowable items.
e.g. “the TBM will encounter Z No. reinforced concrete piles of maximum diameter 600mm at unknown locations between Ch Xm and Ch Ym”

8. Chalk cliff flints & core example

9. Why & where are GBRs used ?
In the UK GBRs are almost exclusively used on Tunneling contracts (though their use elsewhere would probably be beneficial).
The BTS/ABI JCOP states: “Contract documentation for Tunnel Works …. shall include …. Geotechnical Baseline Conditions..”
Tunnel project insurance policies often require compliance with the JCoP.

10. How does a GBR work ?
In the UK via usually via modifications to clause 60.1(12) in an NEC3 contract.
(12) The Contractor encounters physical conditions which
• are within the Site,
• are not conditions of a type referred to in the GBR,
• are not weather conditions and
• an experienced contractor would have judged at the Contract Date to have such a small chance of occurring that it would have been unreasonable for him to have allowed for them.

11. How does a GBR work ? A clause 60.1(12A) is added:
(12A) The Contractor encounters conditions which:
• are within the Site,
• are of a type referred to in the GBR and
• are more adverse than the conditions set out in the GBR
These clauses establish two classes of ‘unforeseen ground condition’ compensation events, each with their own independent data sets that are used to assess the validity of the claim:
The (12A) version, which is only judged on the contents of the hopefully unambiguous and measurable GBR…
...and the (12) version, which is only judged only against contract provided ‘facts’ or reasonably knowable facts. The latter is a traditional vague and inefficient ‘unforeseen ground conditions’ clause.

12. Why give this presentation ?
To raise awareness and encourage promotion of Engineering Geology.
Engineering Geologists routinely create Ground Models (no-one else does) and so they are the principal source of risk knowledge in the ground.
In Ground Models there are always gaps between data points. This is where the ground risk is. These Rumsfeldian ‘known unknowns’ and ‘unknown unknowns’ are our realm. GBRs must address these data gaps in measurable ways.
So it is vital Engineering Geologists are involved in drafting GBRs….
Geotechnical Baseline parameter risk is relatively easy to draft. Geological risk isn’t necessarily so simple to draft...

13. Why give this presentation ?
So we can do geological risk, what other knowledge does the author of a good GBR need ?
The Client’s appetite for risk;
Contracts and contract processes;
Construction processes, especially with regard to TBMs.
This last point is very important as GBRs should provide Baselines that are directly or indirectly measurable in the context of the construction technique. This can be challenging (for anyone), particularly so with TBMs where the ground may only be rarely and intermittently accessible.
Engineering Geologists are well placed to provide GBRs that are less of a geological ‘gamble’.

14. Thankyou Baseline that…. Timber Heading RTD TaMs and grout