Damaged Pile?

[SteelPE]

I have a wood pile that was damaged during driving. From what I have been told, the pile split leaving 70% of the bearing surface in tact. During the procedure, we reissued a repair detail for the location that required the addition of 2 piles to compensate for the eccentricity produced by adding only 1 pile. This was 2-1/2 weeks ago.

Now it is time to form the cap and they find out that they only installed one of the two additional piles. Analysis of the group reveals that the piles are severely overstressed. My solution is to add the pile that was missing. The contractor wants to use the damaged pile and avoid driving another pile. Is the acceptance of a “split” wood pile common and something I have been unaware of?

 

[a2mfk]

Of course he does! You know the answer...

 

[SteelPE]

Of course I do. It's the answer nobody wants to hear.

I'll just leave the contractor alone for a while and see if he comes around to my solution.

 

[msquared48]

In your own words... "Analysis of the group reveals that the piles are severely overstressed."

So, where is the question of what to do?

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[msquared48]

Aside from that point, split pile will rot at the watertable region much faster than intct pile. Install a good one.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[SteelPE]

msquared48,

My analysis was for the group if the damaged pile was ignored. This was a 4 pile group that had one pile split. I reissued a repair that required 5 total (3 existing and 2 new piles in the group. Only 4 were installed (3 existing and 1 of the 2 new piles). The analysis above only was looking at the 4 that were installed. I tried to move the loads around on the pile group to get the cap but was unable to get the group below the allowable. The contractor wanted me to look at including the damaged pile in the analysis.

The good news is that I didn't call them back for a while and now they have come around and are making arrangements to install a new pile. I was just wondering if rejecting the damaged pile is normal in all instances or if there is some criteria for accepting the pile?

 

[Bobber1]

I go with Mike. If it's a treated pile, the treatment only goes so deep. If untreated wood is exposed, the owner is not getting what the owner is paying for.

Bob G.

 

[a2mfk]

I wouldn't fret so much, you did the analysis and it doesn't work. I think this falls under the S#*$ happens category.

Beer-thirty on my watch, have a good weekend everyone!

 

[delagina]

it doesnt make sense to a non-engineer that you are replacing 2 piles for 1 damage pile. it's all vertical loads for them never the moment.

 

[SteelPE]

delagina,

I can see it from their point of view. To my surprise, the geotech thought that you could just add an additional pile. I don't think he had ever run the numbers on a pile group.

 

[BigH]

Question - was the design of the pile based on end-bearing (Likely) or does it derive its capacity on skin friction only? What is the soils you are driving through and bearing on? When I was in NJ and we used a lot of wood piles, an observation I made - approximate - was that the skin friction (and don't forget that you are dealing with a tapered pile - not a straight sided pile - see Nordlund) - the skin friction was typically the "allowable load" after you added the base capacity and put on a 2.5 or so safety factor. In other words, the skin friction was the basis for support and the end bearing the safety factor.

In your case, I would have driven the extra piles as this was what was instructed - but from a forensic point of view I would have looked hard at the where the capacity of the pile/group was being derived and if you had 4 good 'ends' it would probably have been enough. As for the eccentricty - was it outside the normal limits - or just seemed to be a "good choice" - which is perfectly acceptable approach based on experience.

BTW - did your wood piles have tip protection? a steel shoe or ring around the tip?

 

[SteelPE]

Big H,

The decision has already been made and I suspect a new pile will be driven on Monday.... but to answer your question from what I can remember (remember, I am a structural engineer. The piles were being driven through 20 feet of urban fill which was above an organic layer (I think). The piles were developing their capacity based upon skin friction with no end bearing. The urban fill made it very difficult to locate the piles within the planned location (+ tolerance) which cause a whole host of other problems.

I had not inspected the pile personally, but from what I gathered, the damaged had taken place in the upper layers (see fill/organics) and not at the location where we were trying to develop the skin friction. This is why I was slightly unsure. Since we were not using this section of pile to develop skin friction it was essentially acting as a large column delivering the loads to the section that was developing skin friction.

From my experience, I am responsible from the bottom of the cap up... but for some reason the GC was looking to me for a decision. There may be a reason for that.... but I will not get into it.

In the end there were to many question for me to feel comfortable... and the contractor came around to my position once he had some time to think about it.

 

[IFRs]

Can you strengthen the pile cap so it spans the weak pile group to nearby good piles?