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Piling strategies - beamo - 22nd February 2008
I am currently looking at several developments which require careful consideration of the piling strategies with regard to preservation in situ, and would like to throw a few queries out into the knowledgeable world of BAJR.
The recent guidance from EH on Piling and Archaeology (2007) steered clear of endorsing the Arup/York concept that 5% loss of the archaeological remains within a development site would allow for the legibility of the deposits to be maintained (remembering of course that the Arup study was specifically aimed at the nature of the remains anticipated in York and could not be taken to apply elsewhere). In fact the EH paper states that 'developments on archaeologically sensitive sites should strive to achieve lower values'.
Further on the document states 'new piling impact on the site's archaeology should be kept to a minimum, and a loss of no more than 2% of the site should be the target. When all other engineering works are also taken into account, such as services or lift pits, a maximum of 5% of the total site should be seen as the upper limit of loss from foundation construction'.
If I have, for example, a development site within which there are significant archaeological deposits across the whole area, to a depth of 3m+ and waterlogged below 1.5m. What are people's views on:
1. Is the 2% referred to in the EH document 2% of the development site or 2% of the footprint of the built development within the site?
2. Is the 'no more than 2% target loss' actual unrecorded loss (i.e. piling through the deposits unseen), or would each pile location need to be examined and recorded?
This latter question brings up further issues - the piling might be configured to represent a 1% loss of deposits, but in order to safely evaluate/record at 3m depth in waterlogged ground the trenches/test pits would need to be larger than the area actually lost to piling - is this really a preservation in situ strategy? Also we would still be left with a number of relatively small and discrete interventions through a very complicated site and it would be very difficult to relate the deposits in one pile location to those on the neighbouring ones.
The client wants to let out the piling contract as a traditional Design & Build, whereas I would see the piling layout as being driven more through a series of pre-designed layouts aimed at minimising the impact on the archaeological deposits. Does anyone have any recent experience in understanding how piling is procured on sites where archaeology is critical?
Thanks
Beamo
Piling strategies - BAJR Host - 22nd February 2008
http://www.english-heritage.org.uk/upload/pdf/Piling_for_Web_tagged.pdf
for people who wanna see the document
"No job worth doing was ever done on time or under budget.."
Khufu
Piling strategies - drpeterwardle - 22nd February 2008
Beamo said
"Does anyone have any recent experience in understanding how piling is procured on sites where archaeology is critical?"
Yes as it happens I have to say I think it a bit off to have to ask such a question on BAJR when presumabley you or your firm will be paid for your advice.
The key points are:
1. the 5% figure was determined in retrospect based upon Coppergate and like the 2% for evaluations developed into a standard for no good reason.
2. Much lower percentages of destruction can be achieved in some cases it all depends.
3. To my mind there is no particular solution or set figures again it all depends on the circumstances.
4. The pile caps are the things that tend to be destructive rather then the pile themselves depending on the type of piling solution used.
Dr Peter Wardle
(always willing to act as sub-contractor!)
Piling strategies - teamonster - 23rd February 2008
Have you tried discussing this with your Regional Scientific Adviser? They should be able to offer clarification - or if they can't will either check with the other RSAs who co-authored the guidance/put you in touch with them directly to discuss specifics rather than play third party chinese whispers.
EH ran a series of one day workshops on preservation in situ, with particular reference to piling strategies last year - it may be worth seeing if they are repeating the workshops. The day was very useful (and free!).
If you are in a waterlogged site then potential degredation of the remaining waterlogged remains through changes in water table levels may be more significant than a couple of % physical destruction. There is/was some research in York on this that was presented at the IFA conference a couple of years ago that may be worth following up.
Has there been a building there before - could you reuse previous piles?
Piling strategies - drpeterwardle - 23rd February 2008
The preservation of organic archaeological remains (a site can be waterlogged without them being preserved) complicates matters further and is much disputed topic. The key piece on this is in Archaeology in Law Samuels and Pugh Smith in relation to a site in Croydon.
The issue is how will the piling affect the water table and this requires a knowledge of how stable the height of the water table is or how it is changing.
The notion of re-using piles is an attractive one but engineers will be reluctant to do this unless the original calculations are available. One thing that should be done is to configure the design so that in the future the piles can be re-used and make sure the relevant info is properly archived. This of course costs.
Dr Peter Wardle
Piling strategies - historic building - 23rd February 2008
The main issue, and problem, I have experienced with preservation in situ employing piling is how you deal with obstructions, this is especially true where the obstructions are the archaeology and if the site has been previously developed. Short of drilling each pile location with a diamond tipped drill - not a popular choice with developers - this is the primary concern I have as a curator when dealing with this type of solution.
If you are looking at a site which has been previously developed then you will be over any nominal 2% unless previous impacts can be used for piling - drilling through existing locations. Again this is not popular with developers and costs quite a bit.
Talk to a geoarchaeologist at the earliest possible stage to establish the nature of the waterlogging on site and how this has been maintained, and whether piling would seriously impact this characteristic of the site. Any evaluation should be significant enough to enable informed research questions to be answered. Your primary question would be how the waterlogging has been maintained and the likely impacts on this that piling would cause; chasing potential direct impacts from piles, at this stage, may not help you much, but if you are dealing with large, direct impacts that cannot be moved at this stage such as major drainage connections could be useful.
Finally, if you are in a company large enough to have a structural engineer lying around the place, hand them a copy of the piling guidance and take them our for beer once they have read it.
Piling strategies - beamo - 25th February 2008
Many thanks for these responses so far.
I have discussed the sites with which I am dealing with the appropriate EH Regional Science Advisors, both at specific project meetings and also at one of the day schools last year (and I agree with teamonster that this was very useful).
With regard to the particular example site that I mentioned, waterlogging is maintained by high levels of groundwater, even in summer. This would not be affected by the piling. We are currently installing monitoring equipment to assess the baseline chemistry etc in the groundwater. There are few previous impacts from development and no chance of pile reuse (although I accept the concept of configuring the new pile designs so that these could be reused in the future). All non-piling parts of the new development, and the pile-caps, can be contained within the modern made ground above the significant archaeology.
HB - I take your point about obstructions. I remeber one of the case studies in the EH document referred to a site where the piling had been designed to achieve a less than 5% impact, but the need to probe and then move piles around resulted in a much greater area of loss.
Peter - I am sorry if you find it a 'bit off' that I am asking these questions on BAJR. I have considerable experience in dealing with major developments on sensitive archaeological sites, and in the procuring of piling on such sites, but would never think be so smug as to think that I can't learn from the opinions, experiences and advice of my peers. I always thought that was one of the great bonuses of a forum like this one.
Beamo
Piling strategies - Steven - 29th February 2008
Hi Beamo
I'm sure the RSA has described how the impact of piles have a wider "spread" than just the obvious direct damage (for details see PARIS publications or ask your RSA about "cornflake man"s paper at PARIS 3). Therefore (despite EHs "guidance") it is nearly impossible to calculate percentage of damage as the in-direct impacts are entirely dependant many factors. My response to piling schemes is generally to say that unrecorded loss of remains is unacceptable. As archaeological monitoring of piling is generally impossible I would not accept that as mitigation. If its a housing scheme (with gardens etc) I take the application to be a material change of use which allows PD rights to be exercised in the future which threatens remains and therefore require full excavation as the development implies more threat than the direct impact.
In your case perhaps you should forget preservation in-situ because clearly hammering piles through remains (resulting in un-calculable damage) is not preservation. I would go the excavation route as any other solution seems to involve risk.
I don't quite understand your evaluation/recording shorthand as they are completely different beasts aren't they?. If evaluation hasn't taken place why are you getting into mitigation? An evaluation trench shouldn't be dug through archaeological deposits should it? Maybe a few small sondage in specific areas to assess stratigraphy but not wholesale digging through remains.
I am pretty worried that after 18 years of PPG16 that people think we can design our way out of dealing with archaeology by driving big holes into it. Any piling scheme will create un recorded damage, plus compression over time, plus moisture management issues, plus cause problems for the next poor DC archaeologist who has to deal with the demolition and grubbing out, plus not applying the polluter pays principle, plus not really preserving in-situ but really just acting like the proverbial three monkeys.
Not a personal attack Beamo just a general fatigue with bl**dy piling schemes put forward by developers and consultants who quote EH and Arup survey to justify non action.
Steven
Piling strategies - Sparky - 29th February 2008
Hi Steven,
Not wanting to go off the thread and agreeing mostly with what you write, I am slightly concerned about how an archaeological evaluation can evaluate archaeological deposits without actually excavating them. Sondages don't really tell you much about pits or ditches, can be terribly small and fiddly and sometimes misleading on both urban and rural sites. Furthermore, a characterisation of the achaeology, such as dating material, is required for a decision on mitigation. Perhaps you din't quite mean what I thought you did.
A good example of a bad archaeological approach to the sympathies of piling was an outrageous excavation of the pile-holes...yes the holes...at a monastic site in Lincoln. Don't know what was going through the city archaeologist's head; the requirements of the council to develop cheaply, maybe...?
Who is 'Cornflake Man'?
Cheers
S
Piling strategies - Anna Stocks - 3rd March 2008
[quote]Originally posted by Steven
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In your case perhaps you should forget preservation in-situ because clearly hammering piles through remains (resulting in un-calculable damage) is not preservation. I would go the excavation route as any other solution seems to involve risk.
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One quick point - Excavation is not always the best option across a waterlogged site as it can result in a change in the water table (temporary or permanent) of the surrounding non-excavated area, including outside of the development site itself. This could result in the decay of previously waterlogged deposits which would not otherwise be threatened by the development, and have not been recorded during excavation.