Pile Refusal on Very dense Sand
Pile Refusal on Very dense Sand
(OP)
Dear Fellow Engineers,
Anyone have an idea of how to properly analyze the bearing capacity of a driven steel pile that will definitely refuse into very dense soil (N>50) before reaching rock? In other words, I am looking for the end bearing capacity on soil refusal.
Thanks.
Anyone have an idea of how to properly analyze the bearing capacity of a driven steel pile that will definitely refuse into very dense soil (N>50) before reaching rock? In other words, I am looking for the end bearing capacity on soil refusal.
Thanks.





RE: Pile Refusal on Very dense Sand
RE: Pile Refusal on Very dense Sand
RE: Pile Refusal on Very dense Sand
My bearing capacity calculations are based off of experience in similar situations in similar areas. I am sure the pile will refuse on top of solid rock.
Maybe a WEAP analysis would do best.
Please do not try to advise about identifying soils through from split spoons.
Thanks
RE: Pile Refusal on Very dense Sand
Sorry if I offend. Only brought this up because I've seen this to be true many places. On one job (not mine)they had numerous STP borings all calling the very high blow count weathered rock "sand". When the site was opened up, the inspector on the job and the contractor agreed it was a form of rock and you can bet that extra job cost of $ per cubic rock excavation sure taught the geotech report writer a hard lesson. Other negative results from this one case cost the engineer even more. I was only trying to help with my comment question. Glad you are confident with your assessment.
The reason I mentioned now a place in Wisconsin is that there now is a problem there with piles penetrating far into the high blow count "sand" unexpected, very likely a weathered rock situation.
As with questions about how to fix some part that won't come loose on a machine, we sometimes say "Get a bigger hammer". Perhaps that may help here.
Good luck with your situation.
OG
RE: Pile Refusal on Very dense Sand
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RE: Pile Refusal on Very dense Sand
RE: Pile Refusal on Very dense Sand
Thanks a lot for your feedback. I guess get a bigger hammer may help However, then there would be overstress issues just like in WI...
RE: Pile Refusal on Very dense Sand
That would definitely work however the augering will reduce lateral & uplift capacities.
My concern isn't to reach bedrock but rather to properly recommend the correct capacity of a pile when it refuses on soil. In other words I couldn't care less if the pile doesn't reach bedrock I'm just concerned about recommending proper axial downward capacities of a pile.
RE: Pile Refusal on Very dense Sand
Thanks for your question.
I've recommended HP-piles to cut through better as well as closed-ended pipes. Open-ended isn't advisable because of presence of organics.
RE: Pile Refusal on Very dense Sand
An example would be comparing a single-acting Vulcan #1 (15,000 ft-lb, 60 strokes / minute) to a single-acting MKT DE-20 (16,000 ft-lb, 48 strokes /minute).
The Vulcan's 5000 lb. ram free-falling 3 ft., combined with higher blow count rate, will give superior performance to the MKT's 2000 lb. ram free-falling 8 ft.
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RE: Pile Refusal on Very dense Sand
RE: Pile Refusal on Very dense Sand
Secondly, you haven't identified the structure or any settlement criteria - i.e., how sensitive is the structure. Nor have you identified the stratigraphy that you are driving through other than you have 10 ft of very dense sand overlying bedrock nor why you think that you have to "go to rock".
There is no question when driving the close-ended pile, you will refuse in the very dense sand, and not far into it. Is the soil above the very dense sand poor as far as support goes? Are you requiring lateral capacity? These are additional considerations. I would think that you would determine the ultimate bearing and side friction in the "traditional way" - following discussions of maximum values - and go from there. One thing to keep in mind is that even with a pile driven into dense to very dense sand, much of the actual load being carried will be in skin friction/adhesion (which is why I was wondering what the soils above the very dense sand are) with only a limited load carried down to the pile tip. This can be seen in Tomlinson's Figure 7.13 . . . as it takes less movement to mobilized skin friction and more movement to mobilize end-bearing. Unless there was very good reasons not to found in the very dense sand, I am not sure why you wouldn't.
Then, during construction, checks can be made as to confirm your design capacities. Of course, pile load tests are preferred - but that would be on a limited number of piles. As a quick check, the use of the modified Gates dynamic pile driving formula could be used. (http://www1.wisconsindot.gov/documents2/research/0...) I realize that many will not like the use of a dynamic formula but as a check - it can be done on the spot at the end of each driven pile.
RE: Pile Refusal on Very dense Sand