Pile Design (point of fixity)
Pile Design (point of fixity)
(OP)
Dear all,
I have an instance in a pile design where the vertical load is very low such that the point of fixity (which is primarily governed by the diameter of the pile, calculated as per Tomlinson) is deeper than what is required by bearing capacity check. I need a minimum pile diameter in order to practically support the platform above it.
My question is how do i determine where to stop driving my pile in such a case. There should be a practical depth below the point of fixity in order to achieve that point of fixity right?
Ex.
Pile load: 190 kN approx. (SLS)
Pile dia approx. 900 mm
Sea bed level: -8 m
Top of pile: +4 m
Depth of point of fixity below sea bed: 7.5 m
Pile depth required as per bearing capacity check: 6 m below sea bed.
Thanks
VK
I have an instance in a pile design where the vertical load is very low such that the point of fixity (which is primarily governed by the diameter of the pile, calculated as per Tomlinson) is deeper than what is required by bearing capacity check. I need a minimum pile diameter in order to practically support the platform above it.
My question is how do i determine where to stop driving my pile in such a case. There should be a practical depth below the point of fixity in order to achieve that point of fixity right?
Ex.
Pile load: 190 kN approx. (SLS)
Pile dia approx. 900 mm
Sea bed level: -8 m
Top of pile: +4 m
Depth of point of fixity below sea bed: 7.5 m
Pile depth required as per bearing capacity check: 6 m below sea bed.
Thanks
VK






RE: Pile Design (point of fixity)
Have you considered the sea bottom "fluff" in your fixity calculation?
Is there any uplift on the pile?
Have you used L-Pile?
RE: Pile Design (point of fixity)
I tried to consider the lateral load of the pile in order to determine the depth but that again is very small (around 25 kN).
I am sorry but I am not sure what fluff means. There is no uplift. I used hand calculations using Tomlinson.
Thanks
VK
RE: Pile Design (point of fixity)
RE: Pile Design (point of fixity)
RE: Pile Design (point of fixity)
Oh yes, I should have just guessed that. I have assumed that the pile is unsupported upto 1 metre below the sea bed level.
I have not considered any impact loads. That is a fair point.
In any case my doubt still remains. That there are these two independent analyses,
1. Point of fixity calculation
2. Bearing capacity check
It seems more probable (considering my very short experience) that the bearing capacity check will always provide a depth below the point of fixity.
What do we do when it does not?
Thanks.
RE: Pile Design (point of fixity)
Otherwise, I believe you need to provide the larger of the two embedments required. As Ron suggests, you may be able to refine your point of fixity calculations using L-pile or an equivalent spring analysis with the guidance of a geotechnical engineer.
RE: Pile Design (point of fixity)
A time tested "rule of thumb" from the early 20th century predicts that, in good soil, pile embedment = pile projection to resist lateral loads. This indicates (and that is all) that the pile tip should be at approximately Elevation -20. Even that would not be deep enough to ensure fixity at Elevation -15.5.
Things do not add up, recheck your calculations. Also, download "How To Determine Lateral Load Capacity of Piles" from this page of my website: http://www.slideruleera.net/TreatedWood.html
This paper talks about estimating fixity using hand calculations. Don't let the fact that the paper address wood pile deter you, its the same math for other pile materials.
Here is my sketch:
www.SlideRuleEra.net
www.VacuumTubeEra.net