ags ground risk: why take the chance?€¦ · ags ground risk: why take the chance? ground risk –...
TRANSCRIPT
![Page 1: AGS Ground Risk: why take the chance?€¦ · AGS Ground Risk: why take the chance? Ground Risk – Where do I start? Dr Jacqueline Skipper Senior Partner, Senior Geologist . Geotechnical](https://reader033.vdocuments.us/reader033/viewer/2022051607/6035f7f2578de00a0074839f/html5/thumbnails/1.jpg)
AGS Ground Risk: why take the chance? Ground Risk – Where do I start? Dr Jacqueline Skipper Senior Partner, Senior Geologist Geotechnical Consulting Group
![Page 2: AGS Ground Risk: why take the chance?€¦ · AGS Ground Risk: why take the chance? Ground Risk – Where do I start? Dr Jacqueline Skipper Senior Partner, Senior Geologist . Geotechnical](https://reader033.vdocuments.us/reader033/viewer/2022051607/6035f7f2578de00a0074839f/html5/thumbnails/2.jpg)
Ground Risk: why take the chance? A lessons learnt conference
• Where does ground risk begin in engineering projects? • “In the ground, obviously!” – but does it?
![Page 3: AGS Ground Risk: why take the chance?€¦ · AGS Ground Risk: why take the chance? Ground Risk – Where do I start? Dr Jacqueline Skipper Senior Partner, Senior Geologist . Geotechnical](https://reader033.vdocuments.us/reader033/viewer/2022051607/6035f7f2578de00a0074839f/html5/thumbnails/3.jpg)
We live on a planet that is
• Tectonically active • Gravity • Water • Atmosphere and
weather
![Page 4: AGS Ground Risk: why take the chance?€¦ · AGS Ground Risk: why take the chance? Ground Risk – Where do I start? Dr Jacqueline Skipper Senior Partner, Senior Geologist . Geotechnical](https://reader033.vdocuments.us/reader033/viewer/2022051607/6035f7f2578de00a0074839f/html5/thumbnails/4.jpg)
We live on a planet that has
• Plate tectonics • Gravity • Water • Atmosphere and
weather
![Page 5: AGS Ground Risk: why take the chance?€¦ · AGS Ground Risk: why take the chance? Ground Risk – Where do I start? Dr Jacqueline Skipper Senior Partner, Senior Geologist . Geotechnical](https://reader033.vdocuments.us/reader033/viewer/2022051607/6035f7f2578de00a0074839f/html5/thumbnails/5.jpg)
We live on a planet that has
• Plate tectonics • Gravity • Water • Atmosphere and
weather
![Page 6: AGS Ground Risk: why take the chance?€¦ · AGS Ground Risk: why take the chance? Ground Risk – Where do I start? Dr Jacqueline Skipper Senior Partner, Senior Geologist . Geotechnical](https://reader033.vdocuments.us/reader033/viewer/2022051607/6035f7f2578de00a0074839f/html5/thumbnails/6.jpg)
We live on a planet that has
• Plate tectonics • Gravity • Water • Atmosphere and
weather and climates
![Page 7: AGS Ground Risk: why take the chance?€¦ · AGS Ground Risk: why take the chance? Ground Risk – Where do I start? Dr Jacqueline Skipper Senior Partner, Senior Geologist . Geotechnical](https://reader033.vdocuments.us/reader033/viewer/2022051607/6035f7f2578de00a0074839f/html5/thumbnails/7.jpg)
We live on a planet that has
• Plate tectonics • Gravity • Water • Atmosphere and
weather • Humans and what we
do to the planet –
![Page 8: AGS Ground Risk: why take the chance?€¦ · AGS Ground Risk: why take the chance? Ground Risk – Where do I start? Dr Jacqueline Skipper Senior Partner, Senior Geologist . Geotechnical](https://reader033.vdocuments.us/reader033/viewer/2022051607/6035f7f2578de00a0074839f/html5/thumbnails/8.jpg)
This means that the ground is VARIABLE
• If it wasn’t, we wouldn’t be here today • But it is, so we have a primary risk that the ground will vary
![Page 9: AGS Ground Risk: why take the chance?€¦ · AGS Ground Risk: why take the chance? Ground Risk – Where do I start? Dr Jacqueline Skipper Senior Partner, Senior Geologist . Geotechnical](https://reader033.vdocuments.us/reader033/viewer/2022051607/6035f7f2578de00a0074839f/html5/thumbnails/9.jpg)
Example - sediments Variable sediments can be • confusing • weaker • stronger • less or more cemented • often less stable • more permeable/porous and • at different levels,
– to what was expected (from the information available/provided)
![Page 10: AGS Ground Risk: why take the chance?€¦ · AGS Ground Risk: why take the chance? Ground Risk – Where do I start? Dr Jacqueline Skipper Senior Partner, Senior Geologist . Geotechnical](https://reader033.vdocuments.us/reader033/viewer/2022051607/6035f7f2578de00a0074839f/html5/thumbnails/10.jpg)
Ground risk based on depositional environment
Fairly low ground
risk
Medium ground
risk
Fairly low ground
risk
Medium to high ground
risk
High ground
risk
Sediments deposited in these areas are likely to be:
![Page 11: AGS Ground Risk: why take the chance?€¦ · AGS Ground Risk: why take the chance? Ground Risk – Where do I start? Dr Jacqueline Skipper Senior Partner, Senior Geologist . Geotechnical](https://reader033.vdocuments.us/reader033/viewer/2022051607/6035f7f2578de00a0074839f/html5/thumbnails/11.jpg)
Variable sediments • Have a wider range of properties,
and perversely, are:
• More difficult to recover
• More difficult to obtain data for
• More difficult to correlate
• More challenging to design for/construct in
• Thereby increase project ground RISK
![Page 12: AGS Ground Risk: why take the chance?€¦ · AGS Ground Risk: why take the chance? Ground Risk – Where do I start? Dr Jacqueline Skipper Senior Partner, Senior Geologist . Geotechnical](https://reader033.vdocuments.us/reader033/viewer/2022051607/6035f7f2578de00a0074839f/html5/thumbnails/12.jpg)
Also, these secondary mechanisms increase complexity, often superimposing on one another
1. Environments of deposition 2. Post depositional changes (chemical, biological,
physical weathering) 3. Tectonic changes e.g. faulting, uplift, 4. Quaternary big changes e.g. T↓↑, SL ↓↑
erosion, slope failures 5. Anthropocene effects e.g. mining, construction,
contamination
![Page 13: AGS Ground Risk: why take the chance?€¦ · AGS Ground Risk: why take the chance? Ground Risk – Where do I start? Dr Jacqueline Skipper Senior Partner, Senior Geologist . Geotechnical](https://reader033.vdocuments.us/reader033/viewer/2022051607/6035f7f2578de00a0074839f/html5/thumbnails/13.jpg)
Ground risk is very expensive. Why do we need to keep having to say this?
• Failing to anticipate ground conditions is a major factor in construction problems Fookes 1997
• 50% of project delays caused by adverse ground conditions Chapman & Marcetteau 2004
• Ground risk = 50% reduction in return on client’s equity Chapman 2006
• 80-85% of (European) building failures are related to ground problems Brandl, 2004
![Page 14: AGS Ground Risk: why take the chance?€¦ · AGS Ground Risk: why take the chance? Ground Risk – Where do I start? Dr Jacqueline Skipper Senior Partner, Senior Geologist . Geotechnical](https://reader033.vdocuments.us/reader033/viewer/2022051607/6035f7f2578de00a0074839f/html5/thumbnails/14.jpg)
And, even with best EC7 practice
• Even with best borehole spacings/depths, recovery represents 0.008% of the ground
• This is for 100% recovery, rotary boreholes • This % drops with
– wider spacings (e.g. linear infrastructure 0.003%) – other drilling techniques – variable ground conditions/poor recovery
• GIs are frequently not a 100% accurate representation – even in the precise locations in which they are carried out
![Page 15: AGS Ground Risk: why take the chance?€¦ · AGS Ground Risk: why take the chance? Ground Risk – Where do I start? Dr Jacqueline Skipper Senior Partner, Senior Geologist . Geotechnical](https://reader033.vdocuments.us/reader033/viewer/2022051607/6035f7f2578de00a0074839f/html5/thumbnails/15.jpg)
Despite this, thorough ground investigations are a good idea!
• GIs can significantly reduce ground risk uncertainty • But only 0.2% to 0.5% construction costs are spent on GI! • Why is this?
![Page 16: AGS Ground Risk: why take the chance?€¦ · AGS Ground Risk: why take the chance? Ground Risk – Where do I start? Dr Jacqueline Skipper Senior Partner, Senior Geologist . Geotechnical](https://reader033.vdocuments.us/reader033/viewer/2022051607/6035f7f2578de00a0074839f/html5/thumbnails/16.jpg)
What blocks our understanding of ground variability and risks?
And is therefore invisible
Here’s a couple of examples of preconceptions…
Most of the ground is
![Page 17: AGS Ground Risk: why take the chance?€¦ · AGS Ground Risk: why take the chance? Ground Risk – Where do I start? Dr Jacqueline Skipper Senior Partner, Senior Geologist . Geotechnical](https://reader033.vdocuments.us/reader033/viewer/2022051607/6035f7f2578de00a0074839f/html5/thumbnails/17.jpg)
The geology
The Engineer* thinks
Shiny challenging thing, pays our wages!
Perplexing challenging geology to build things on/through.. “It’s all London Clay anyway”
* Very smart engineers who understand geology in detail are also available
![Page 18: AGS Ground Risk: why take the chance?€¦ · AGS Ground Risk: why take the chance? Ground Risk – Where do I start? Dr Jacqueline Skipper Senior Partner, Senior Geologist . Geotechnical](https://reader033.vdocuments.us/reader033/viewer/2022051607/6035f7f2578de00a0074839f/html5/thumbnails/18.jpg)
The Geologist thinks
Thing being built. Who cares what it is, it pays wages?
Wow! Opportunity to study the geology!
![Page 19: AGS Ground Risk: why take the chance?€¦ · AGS Ground Risk: why take the chance? Ground Risk – Where do I start? Dr Jacqueline Skipper Senior Partner, Senior Geologist . Geotechnical](https://reader033.vdocuments.us/reader033/viewer/2022051607/6035f7f2578de00a0074839f/html5/thumbnails/19.jpg)
What else affects perception?
Different contract forms + different preconceptions
![Page 20: AGS Ground Risk: why take the chance?€¦ · AGS Ground Risk: why take the chance? Ground Risk – Where do I start? Dr Jacqueline Skipper Senior Partner, Senior Geologist . Geotechnical](https://reader033.vdocuments.us/reader033/viewer/2022051607/6035f7f2578de00a0074839f/html5/thumbnails/20.jpg)
The Experienced Client thinks
“Shiny thing make money, but maybe a GBR would serve us best?”
“We’ve been stung before by these ground conditions, let’s make sure we get a good ground investigation”
![Page 21: AGS Ground Risk: why take the chance?€¦ · AGS Ground Risk: why take the chance? Ground Risk – Where do I start? Dr Jacqueline Skipper Senior Partner, Senior Geologist . Geotechnical](https://reader033.vdocuments.us/reader033/viewer/2022051607/6035f7f2578de00a0074839f/html5/thumbnails/21.jpg)
The less experienced Client perhaps thinks
Shiny building make money!
• Don’t understand the ground- pass the risk to the contractor.
• We don’t have time for an extensive GI
• Savings can be made on the ground investigation!
![Page 22: AGS Ground Risk: why take the chance?€¦ · AGS Ground Risk: why take the chance? Ground Risk – Where do I start? Dr Jacqueline Skipper Senior Partner, Senior Geologist . Geotechnical](https://reader033.vdocuments.us/reader033/viewer/2022051607/6035f7f2578de00a0074839f/html5/thumbnails/22.jpg)
What if the contractor carries the risk?
• ‘We assumed favourable ground conditions to price cheaply and win the work’
• ‘We don’t want to pay for more GI – the client has done a basic Factual Report’
• ‘We can always claim unforeseen ground conditions’
![Page 23: AGS Ground Risk: why take the chance?€¦ · AGS Ground Risk: why take the chance? Ground Risk – Where do I start? Dr Jacqueline Skipper Senior Partner, Senior Geologist . Geotechnical](https://reader033.vdocuments.us/reader033/viewer/2022051607/6035f7f2578de00a0074839f/html5/thumbnails/23.jpg)
Can this lead to the perfect geotechnical storm? Cheapest ground investigation tender, short deadline Negligible Desk Study (‘what was the exam question?’) Inappropriate investigative methods Poor recovery Unrepresentative sampling Poor logging conditions! Poor descriptions Poor sample care
→ Unrepresentative lab test results • Unsuitable design for ground conditions • Construction problems due to ground conditions • Cost to client – overruns, lawyers etc £££
![Page 24: AGS Ground Risk: why take the chance?€¦ · AGS Ground Risk: why take the chance? Ground Risk – Where do I start? Dr Jacqueline Skipper Senior Partner, Senior Geologist . Geotechnical](https://reader033.vdocuments.us/reader033/viewer/2022051607/6035f7f2578de00a0074839f/html5/thumbnails/24.jpg)
Sadly
• It is often not until things go wrong that the risk bearer is prepared to get an appropriate GI
![Page 25: AGS Ground Risk: why take the chance?€¦ · AGS Ground Risk: why take the chance? Ground Risk – Where do I start? Dr Jacqueline Skipper Senior Partner, Senior Geologist . Geotechnical](https://reader033.vdocuments.us/reader033/viewer/2022051607/6035f7f2578de00a0074839f/html5/thumbnails/25.jpg)
Ground data loss = increased ground risk
????
Designer
?????
Contractor Logger
??
Lawyer
!!!!!
Driller
?
Lab
???
![Page 26: AGS Ground Risk: why take the chance?€¦ · AGS Ground Risk: why take the chance? Ground Risk – Where do I start? Dr Jacqueline Skipper Senior Partner, Senior Geologist . Geotechnical](https://reader033.vdocuments.us/reader033/viewer/2022051607/6035f7f2578de00a0074839f/html5/thumbnails/26.jpg)
And ground risk in the contract comes first
Contract
![Page 27: AGS Ground Risk: why take the chance?€¦ · AGS Ground Risk: why take the chance? Ground Risk – Where do I start? Dr Jacqueline Skipper Senior Partner, Senior Geologist . Geotechnical](https://reader033.vdocuments.us/reader033/viewer/2022051607/6035f7f2578de00a0074839f/html5/thumbnails/27.jpg)
Unforeseen ground - a landmark case …
“Every experienced contractor knows that ground investigations can only be 100% accurate in the precise locations in which they are carried out. It is for an experienced contractor to fill in the gaps and take an informed decision as to what the likely conditions would be overall”. Mr Justice Coulson, Van Oord UK Limited and SICIM Roadbridge Limited v Allseas UK Limited [2015]
![Page 28: AGS Ground Risk: why take the chance?€¦ · AGS Ground Risk: why take the chance? Ground Risk – Where do I start? Dr Jacqueline Skipper Senior Partner, Senior Geologist . Geotechnical](https://reader033.vdocuments.us/reader033/viewer/2022051607/6035f7f2578de00a0074839f/html5/thumbnails/28.jpg)
In other words
• If you carry the risk, • You can’t plead ignorance • You must do additional GI if the original was not appropriate
for the probable variability of the ground • Keep up with the current state of knowledge!
![Page 29: AGS Ground Risk: why take the chance?€¦ · AGS Ground Risk: why take the chance? Ground Risk – Where do I start? Dr Jacqueline Skipper Senior Partner, Senior Geologist . Geotechnical](https://reader033.vdocuments.us/reader033/viewer/2022051607/6035f7f2578de00a0074839f/html5/thumbnails/29.jpg)
Faulting bringing Lambeth Group to near surface position, UCLH Cancer Centre
Two examples of already complex ground (Lambeth Group+ London Clay) related to faulting in London
![Page 30: AGS Ground Risk: why take the chance?€¦ · AGS Ground Risk: why take the chance? Ground Risk – Where do I start? Dr Jacqueline Skipper Senior Partner, Senior Geologist . Geotechnical](https://reader033.vdocuments.us/reader033/viewer/2022051607/6035f7f2578de00a0074839f/html5/thumbnails/30.jpg)
What happened?
• Faulting only discovered coincidentally • Minor pile failures managed between designer and contractor • Historical data showed previous adjacent site adversely
affected by faulting + sand channels - open bored piles affected • Short paper in Ground Engineering to publicise • Other sites in the area are also affected but lessons have been
learnt
![Page 31: AGS Ground Risk: why take the chance?€¦ · AGS Ground Risk: why take the chance? Ground Risk – Where do I start? Dr Jacqueline Skipper Senior Partner, Senior Geologist . Geotechnical](https://reader033.vdocuments.us/reader033/viewer/2022051607/6035f7f2578de00a0074839f/html5/thumbnails/31.jpg)
The site is within a zone of unusual ground conditions with complex faulting of London Clay and sand channels within the Lambeth Group
![Page 32: AGS Ground Risk: why take the chance?€¦ · AGS Ground Risk: why take the chance? Ground Risk – Where do I start? Dr Jacqueline Skipper Senior Partner, Senior Geologist . Geotechnical](https://reader033.vdocuments.us/reader033/viewer/2022051607/6035f7f2578de00a0074839f/html5/thumbnails/32.jpg)
Strike-slip structural ground model.
Explains complex faulted areas of
ground in localised areas
![Page 33: AGS Ground Risk: why take the chance?€¦ · AGS Ground Risk: why take the chance? Ground Risk – Where do I start? Dr Jacqueline Skipper Senior Partner, Senior Geologist . Geotechnical](https://reader033.vdocuments.us/reader033/viewer/2022051607/6035f7f2578de00a0074839f/html5/thumbnails/33.jpg)
A’ 10
0
-10
-20
-30
-40
-50
-60
-70
Met
res O
D
A PBH13
PBH3
PBH5
PBH9
PBH10 PBH14
PBH4
PBH6
A3ii
A2
A3ii
A2
A3ii
A3i
A2
A3ii
A2
A3ii
A2 A3ii
A2 A3i
A3ii
A3i A2
A3ii
A2
A3i
A3ii
A3i
A2
Site with a ‘silt filled hollow’ and a river across the site
![Page 34: AGS Ground Risk: why take the chance?€¦ · AGS Ground Risk: why take the chance? Ground Risk – Where do I start? Dr Jacqueline Skipper Senior Partner, Senior Geologist . Geotechnical](https://reader033.vdocuments.us/reader033/viewer/2022051607/6035f7f2578de00a0074839f/html5/thumbnails/34.jpg)
What happened?
• Many previous phases of GI, desk studies • ‘Lost Rivers’ and ‘Silt Pocket’ raised suspicions – faulting? • Reassessment of GIs found evidence of faults • Communication with client and designers about potential risks
led to improved GI • GI – weakened ground, faulting ++ • Discovery of a number of issues for piling
![Page 35: AGS Ground Risk: why take the chance?€¦ · AGS Ground Risk: why take the chance? Ground Risk – Where do I start? Dr Jacqueline Skipper Senior Partner, Senior Geologist . Geotechnical](https://reader033.vdocuments.us/reader033/viewer/2022051607/6035f7f2578de00a0074839f/html5/thumbnails/35.jpg)
A’ 10
0
-10
-20
-30
-40
-50
-60
-70
Met
res O
D
A PBH13
PBH3
PBH5
PBH9
PBH10 PBH14
PBH4
PBH6
A3ii
A2
A3ii
A2
A3ii
A3i
A2
A3ii
A2
A3ii
A2 A3ii
A2 A3i
A3ii
A3i A2
A3ii
A2
A3i
A3ii
A3i
A2
Complex faulting, silt hollow related to faulting
![Page 36: AGS Ground Risk: why take the chance?€¦ · AGS Ground Risk: why take the chance? Ground Risk – Where do I start? Dr Jacqueline Skipper Senior Partner, Senior Geologist . Geotechnical](https://reader033.vdocuments.us/reader033/viewer/2022051607/6035f7f2578de00a0074839f/html5/thumbnails/36.jpg)
MOVE structural geological modelling © R. Ghail, Imperial College.
![Page 37: AGS Ground Risk: why take the chance?€¦ · AGS Ground Risk: why take the chance? Ground Risk – Where do I start? Dr Jacqueline Skipper Senior Partner, Senior Geologist . Geotechnical](https://reader033.vdocuments.us/reader033/viewer/2022051607/6035f7f2578de00a0074839f/html5/thumbnails/37.jpg)
Failure to recognise how others see the ground can itself constitute a risk
• If we don’t understand professional differences, information or advice can be misunderstood or ignored
• Conversely, trying too hard to please (e.g. a client) can cause us to lose trust in our own professional judgement.
![Page 38: AGS Ground Risk: why take the chance?€¦ · AGS Ground Risk: why take the chance? Ground Risk – Where do I start? Dr Jacqueline Skipper Senior Partner, Senior Geologist . Geotechnical](https://reader033.vdocuments.us/reader033/viewer/2022051607/6035f7f2578de00a0074839f/html5/thumbnails/38.jpg)
What lessons can be learnt? • Relevant competence is essential from the beginning of a project to address ground
risk • Be wary of developers/clients and be aware of who controls risk • Give clients direct and honest, recorded advice, being aware of differing priorities • Do not adopt GI reports without question – do additional GI if necessary • Be wary of how design responsibility slides down the contract chain • Ensure time resources are adequate • Clarify roles and responsibilities • Trust your own professional opinion and STOP when necessary • Communicate, publish – pass on the ground knowledge!