In need of a definition
In need of a definition
(OP)
I am looking for a definition, but need some substantiation (a quote from a text book or other source)
Is a raft foundation a structure supported directly by the underlying soil or can it also include a foundation supported by piles?
Any help appreciated.
Is a raft foundation a structure supported directly by the underlying soil or can it also include a foundation supported by piles?
Any help appreciated.





RE: In need of a definition
A piled raft is a foundation where some the load is distributed between the piles and the soil beneath the raft.
RE: In need of a definition
RE: In need of a definition
RE: In need of a definition
my understanding is as you suggest. In which case if I price for a raft foundation I don't expect to have to excavate around piles, I also don't expect to be told that I have to cut down someone else's precast driven piles included my raft foundation price.
But as mentioned above there is some lack of clarity in the usage of the term "raft" and that with an absence of a method of measurement is enough to cause a confusion. As is fairly common the owner's consultant suggests we just do the work and "sort it out later".
RE: In need of a definition
Sowers doesn't contemplate pile support for mats. He considers them to be soil supported.
Lambe doesn't clearly define a mat, but considers it just a shallow foundation variant.
RE: In need of a definition
thanks. This lack of clarity means that I am now faced with a difficult situation in Vietnam. The owner's consultant says we should have realised from the borehole logs that piles would be required (we are not responsible for design) and therefore we should have allowed for excavation around the piles and cutting at cut-off level.
We didn't allow for this we just priced an itemised BQ for the works based on 2 tender drawings.
RE: In need of a definition
Given that, the approach I would take is that the plans should have shown piles if they were required. To show only the mat foundation and provide boring logs that they expect YOU to interpret and offer further foundation design is absurd. You are the contractor. You are not required to design the project (unless of course you have a design-build contract).
RE: In need of a definition
RE: In need of a definition
@ishvaaag: seems that this is not the case - most use piled-raft foundation; probably depends on the country (remember our discussions of what is a bored pile or a drilled caisson, etc). See: htt
http://www.ejge.com/2009/Ppr0906/Ppr0906s.pdf
Varghese (Indian) says, "A raft or mat foundation consists of a large concrete slab or a slab and beam system resting on soil or rock and supporting all the lods through a num ber of columns or walls. When the raft is supported by piles it is called a piled raft.
I've always considered "raft" and "mat" to be interchangably the same.
RE: In need of a definition
There is no QS but the owner's engineer says piles weren't mentioned because they are not in our scope of work. However he is of the opinion that as we would have known there would be piles by looking at the borehole logs. He also states that as it is common practice in Vietnam that the foundation contractor cuts the piles to level then we are deemed to have included this in our price.
This is not a design and build project.
RE: In need of a definition
at the time of pricing there was no discussion about piles. But some time has elapsed now and in the interim we have become aware that piles were being driven by another contractor. There are 2 issues.
Firstly cutting the piles and taking away the cut off lengths which we originally assumed the piling contractor would do, secondly excavating around the piles which we have only just realised as a valid claim for an increase of rate. The second item is negotiable and depends whether they intend to reduce our excavation quantity due to the volume of the piles.
RE: In need of a definition
please give the title of the book by Varghese (as a useless bit of info I recall that that is a Christian family name)we do seem to be coming to the conclusion that a "raft" is a raft and a "piled raft" has piles.
RE: In need of a definition
It is quite a stretch to expect a subcontractor to infer that a building is to be pile supported based on boring logs. If you were given a complete geotechnical report which excluded shallow footing systems, the owner's engineer might have an argument.
RE: In need of a definition
1. The piling contractor should cut the tops to the required elevation. They are his piles and you do not want to get into further liability of potentially damaging his work by cutting them yourself. This should not even be an issue on your part...not your job.
2. If piles were not anticipated in your bid, and you had nothing other than boring logs and insufficiently detailed plans, you should have a valid claim for extra pay for the more tedious and time consuming excavation around piles...again you have to be more careful not to damage the pile contractor's work.
As for the mat/raft designation, I've heard them throughout my career to be interchangeable; however, BigH's statements make sense...I'm just not sure that most use the vernacular in that manner. As for pile support, it generally is stated if they are pile supported (piled mat, piled raft, pile-supported mat, etc.).
Is there anything indicative in the design of the mat reinforcing that would lead you to conclude that there is a pile interface?
RE: In need of a definition
RE: In need of a definition
RE: In need of a definition
Zambo:
P.C. Varghese, Foundation Engineering, Prentice-Hall of India, 2005. ISBN-81-203-2652-0/
RE: In need of a definition
Vietnam is a bit "wild west" but with a few facts gathered together the owner will probably see sense.
RE: In need of a definition
Bingo - free kick. If they are not in your scope of work then you are not expected to do any work related to them.
I really cannot see how they can wriggle out of that one if you have it in writing.
RE: In need of a definition