Pile Size
Pile Size
(OP)
I'm getting an enormous amount of grief for a project I'm on in Florida. I'm a structural engineer for this project and am not a pile expert. My Geotechnical Consultant gave me this design and seems to be quite confident.
The design involves 528-12 inch square prestressed concrete piles spaced at 6'-6". The piles are to be driven into a 15 foot predrilled hole until they meet refusal of 20 blows per inch. The minimum depth (beyond the predrilled hole) is 40'-0". Design load for each pile is 50 tons.
The contractor has been griping about the piles even during the pre-bid. He says he needs 14 inch piles and that's what he bid. He won't give any details on why he thinks this.
Since the pile spacing is based on the size, I'm worried I'm going to have to change my layout. Plus the larger piles will need more driving force and possibly damage adjacent structures.
Does anyone else see a problem with the 12 inch piles?
The design involves 528-12 inch square prestressed concrete piles spaced at 6'-6". The piles are to be driven into a 15 foot predrilled hole until they meet refusal of 20 blows per inch. The minimum depth (beyond the predrilled hole) is 40'-0". Design load for each pile is 50 tons.
The contractor has been griping about the piles even during the pre-bid. He says he needs 14 inch piles and that's what he bid. He won't give any details on why he thinks this.
Since the pile spacing is based on the size, I'm worried I'm going to have to change my layout. Plus the larger piles will need more driving force and possibly damage adjacent structures.
Does anyone else see a problem with the 12 inch piles?





RE: Pile Size
RE: Pile Size
The contractor is saying nothing except he doesn't like what we have.
RE: Pile Size
RE: Pile Size
RE: Pile Size
I'm sure a meeting is in order, but I'm trying to get my thoughts in line.
RE: Pile Size
The issue may be with splices. Many piling companies are only set up to splice certain sizes, and I think 14" is a common one.
RE: Pile Size
RE: Pile Size
RE: Pile Size
Pile driving,depite all the hype, is not an exact science. For 528 piles at 55 feet and lets say $40 per ft, you are over $1,000,000. Such a program should, even without contractor's questions, should have a test pile program. Drive a number of teat piles, I would say 5, with wave eqaution, PDA and at least one static load test. If you have vibration concerns, moniter structures durring driving. If the pile works, the pile works, if not,the design needs to be revised. In any event, production piles should not be ordered until the results of the test pile program are digested.
RE: Pile Size
RE: Pile Size
RE: Pile Size
RE: Pile Size
RE: Pile Size
Two possible reasons for the contractor's atitude occur to me:
First, maybe the contractor has a line on some cheap 14-inchers
left over from another project.
If so, he should share the wealth, IMO.
But maybe his proposal reflected that.
Second, perhaps the contractor has gotten 'in trouble' driving 12-inch
piles in the region. If so, it can be dangerous to discount local experience.
FYI, I believe FDOT still requires a minimum 18-inch pile cross section.
Factors such as corossion and driving stress through hard limestone might be an issue.
RE: Pile Size
RE: Pile Size
RE: Pile Size
Once they submit their piles and start the testing program, maybe we can pin them down. As I mentioned before, the Geotechnical Engineer is responsible for the pile design, inspecting and administering the pile program. However, for now, I'm the first ear bent.
Thank you all for your input.
RE: Pile Size
RE: Pile Size
Long story short, there doesn't appear to be anything wrong with the 12 inch piles, except they result in a more expensive end product.
RE: Pile Size
RE: Pile Size
Simply adding all the piles on the job and multiplying by the orginal capacty and dividing by a new capacity will not give you the number of piles on the job. Some locatons will require a fixed number of piles regardles of capcity.
What Van Komurka suggested, the most economical approach is to select several pile sizes, say 3-5 different piles.
Capacity can be varried by length or size.
He gave the talk at "Design of Cost Efficent Piles" sponsered by the Pile Drivers Contractors Association in New Orleans.
As for auger cast piles, I have not heard of these being used with much sucess except for low capacities. For high capacities, driven piles have much better quality control and an be installed quickly.
RE: Pile Size
We design & install continuous flight auger (CFA) & DeWaal piles (DWP), as well as drive precast piles, micro-piles, etc. Under the right conditions, driven piles are the proper choice - we have driven thousands of them.
CFA piles have been used for design capacities up to 1500 tons (1m diameter CFA in Las Vegas - Wynn Tower).
CFA piles are quite different from conventional auger cast in place piles (ACIP) and installed with a high torque auger that minimizes soil sidewall disturbance and hence ensures intimate contact w/ the soils and high pile capacities. We routinely use 100 ton designs for 14" DWP. DWP are actually augered displacement piles which keep all soil cuttings in the hole thereby increasing the soil density and maximizing pile capacity. In most cases except for dense/hard soils DWP's will far outperform driven piles in capacity and installation time. This has been recently proven through a series of 100 pile load tests on all 3 pile types for a huge project (50,000 piles).
We are currently installing DWP's at oil refineries in LA & TX, where our production is 20+ piles per rig/day to 60-80'.
Using 3-5 different pile sizes may appear to be economical, but it often slows field production because of the equipment change.
cheers,
Rick
Morris-Shea Bridge Co.
morrisshea.com
RE: Pile Size
This type of bid is just asking for some contractor to "underestimate" the amount of piles, and make it up on allowances. Theoretically it's cheaper, but how could you implement it?
RE: Pile Size