pile engineering solution
pile engineering solution
(OP)
I already finished designing a pile foundation in which the flooring is considered as slab on grade. after driving all the piles in the ground, there was a change in the structural system, instead of using slab on grade we dicided to design it as structural slab because of settlement problem.
After checking the pile capacity that is considering the additional weight coming from the structural slab,grade beam and soil, i notice that the pile reaction exceeds the pile capacity. i am thinking to to add additional piles besides the critical pile making it 3 piles to distribute the pile reactions.
I want to hear your opinions about this. I appreciate if you can suggest other solutions.
After checking the pile capacity that is considering the additional weight coming from the structural slab,grade beam and soil, i notice that the pile reaction exceeds the pile capacity. i am thinking to to add additional piles besides the critical pile making it 3 piles to distribute the pile reactions.
I want to hear your opinions about this. I appreciate if you can suggest other solutions.






RE: pile engineering solution
Jeff
RE: pile engineering solution
RE: pile engineering solution
RE: pile engineering solution
RE: pile engineering solution
It should be no surprise that your piles are overloaded by adding one entire concrete floor, complete with live load. The best advice I can offer is to follow the recommendations of your geotechnical engineer. Add piles as required and you won't have to deal with settlement problems a year or two from now.
BA
RE: pile engineering solution
In short, we are not demanding ordinarily settlements anywhere that won't never be surpassed, but those that experience and reasonable computation show it is reasonable to expect.
RE: pile engineering solution
any opinion i this issue would help me a lot. thanks in advance.
RE: pile engineering solution
Mike McCann
MMC Engineering
RE: pile engineering solution
If there was a soil report prior to design, why was the settlement problem not recognized prior to driving all of the piles? What recommendations did the geotech make originally respecting the slab on grade? What does he have to say about the decision to use a structural slab on grade now? Is there another alternative such as removing questionable soil and placing engineered fill between piles?
You stated:
Are the driven piles timber, steel, precast concrete or other? How are they attached to the pile caps? What is the soil type at the site?
How can you expect a reasonable answer to your question based on the scant information you have provided?
BA
RE: pile engineering solution
There is a soil report prior to driving of piles. It was only recommended there to use concrete piles. we just found out lately that there is an issue of settlement of slab in the neighboring structure. I try to re anlyze the structure using fixed support and spring for pile and i observe that the recation decreases thats why i rised a question regarding pile support. The soil bearing capacity is 60KPa.
RE: pile engineering solution
Request the geotech firm to do additional testing on your site and make recommendations as to the most appropriate measures to be taken to support the grade slab. A structural slab is one possibility but there are others.
As to your question about boundary conditions at the support, a pile is not a fixed support. It is a beam on an elastic foundation, the soil providing elastic reactions throughout the length of pile. How close the support is to full fixity depends of the properties of the pile and the soil.
BA
RE: pile engineering solution
RE: pile engineering solution
the piles are 6m apart, 16 m in length and 600mm diameter. The option that i did is to put a spring support (location of piles) along vertical axis with a spring onstant of k=AE/L and provide fixity on the horizontal axis and restained moment. I just want to clarify that the pile cap is not included in the model.
Just to ask some clarification on what you said " It is a beam on an elastic foundation, the soil providing elastic reactions throughout the length of pile". Does it mean that the pile is release in the horizontal axis?
Thanks.
RLC
RE: pile engineering solution
If it is a friction pile, the resistance to the vertical reaction is presumed to occur uniformly from top to bottom. That may not be true if the soil characteristics are variable within the length of pile, but it is probably about as close as you can guess. In that case, the vertical deflection at top of pile would be approximately FL/2AE, i.e. using the half length instead of the full length.
If the pile is an end bearing pile, the resistance to vertical load occurs at the bottom, so the vertical deflection at top of pile will be FL/AE + F*Ks where Ks represents a spring constant for a load on the soil.
When I said the pile is a beam on an elastic foundation, I was thinking about a moment applied at the top. If the pile is pinned top and bottom and there is no soil around the shaft, the pile bends as a simple beam and its horizontal deflection can be calculated at any height by elementary theory.
Because the pile is surrounded by soil, it is not free to deflect sideways. The soil will resist that movement. If the soil is considered to be an elastic material, the pile may be considered as a beam on an elastic foundation. The support could then be represented as a rotational spring plus a vertical spring.
It is not clear to me how this approach is going to significantly change the load on each pile. If the additional reaction of the structural slab adds too much load to the piles, you must either add piles or find another way to support the slab on grade.
BA
RE: pile engineering solution
RE: pile engineering solution
In RLC's first post he said the piles were driven in the ground. If they are concrete piles, they must be precast.
I agree that the soil profile and a description of the building would be of interest.
BA
RE: pile engineering solution
You are right, he did say they are driven piles. I would just ask him to confirm that, as 600 mm driven piles are not common. Uncommon enough that I have never seen or heard of precast concrete piles of that size. Could they be driven cast in place piles (Franki or similar)?