Piling Problem

[kieran1]

I have a situation where load bearing piles have been installed behind a proposed jetty. The contractor has said the piles were installed to refusal, which I doubt.

It is proposed to dredge the area under the piles after a concrete beam is cast, to a level 6.0m below water level. The piles are 11.8m long and top of pile level is 5.73m above water level. This leaves an embedment depth of only 70mm.

This is my concern. I was not involved until after the piles were installed. My thoughts are to not allow any dredging, but this will render the project unworkable.

Anyone any suggestions.

I'm thinking of sand bags in front of the piles to prevent the soil in this area from being removed. This is in Africa so tremie concrete and any solution which requires western technology is not possible. The jetty line is only 2.0m from the pile line.

Kieran

 

[msquared48]

Africa, huh?

Well then I assume there are no pile logs or formal documentation to back up the contractor's claim...

How big of a bond did the contractor post, if any?

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

 

[kieran1]

No Pile Logs, No bond, No nothing and you would not believe some of the previous projects this contractor has undertaken around the world. Very famous projects.

But unfortunately i'm left to sort it out, with very little resources. Need some "out of the box" thinking and ideas.

Kieran

 

[msquared48]

Well, you need the refusal of the pile proven to you, correct? If so, then make him prove it to you. Has he been paid in full for the work to date? And does he have any work to do yet on the contract?

After getting the OK to do this from your superiors, make him an offer that's hard to refuse. Tell him that you need the refusal proven to you since it is a safety issue. He needs to test, say "X" number of pile of your choosing. If they are OK, he will be paid for the test. If not, every pile will be tested at his expense and driven to the proper depth within "Y" number of workdays.

If he does not want to do that, get a contractor who will, charge him for the testing, and don't use him again, low bidder or not. Let him know that your company will make sure that his professional reputation will be impacted, diplomatically.

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

 

[kieran1]

He has already moved off site. Crazy thing is the piles (Steel CHS) were not even long enough to extend to underside of concrete beam level. I've had to arrange additional sections to be welded on to extend the piles, some by up to 2m. Then I find out about the dredging level.

Contractor has been paid, as far as I know. Absolute amateurs running this job before I arrived.

Very tempted to walk at this stage.

Kieran

 

[msquared48]

Might be a REAL good idea.

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

 

[Ron]

kieran1...agree with Mike...probably a good time to haul a$$. If you can't, then consider PDA to check capacity. I would probably opt for splicing and driving deeper. I would not allow dredging at this point.

 

[Zambo]

I've worked in West Africa a few times and with good contractors, using skilled supervision good quality work can be achived.

I'm not sure I entirely understand the situation you are describing. Can you confirm the following:

1. you have a CHS pile wall which is running parallel to the shore (or whatever land you have).

2. perpendicular to the CHS pile wall there will be a future jetty extending out to the sea.

3. the piles are approx 11.8m long with 5.8m above water and 6m below water. Now it is planned to dredge to a full 6m depth below water level. In this case the pile toe embedment will be 70mm (nominally zero).

4. the only thing which will keep the piles in place will be the concrete beam at the top of the piles.

But now I wonder if the above is correct. Is this a wall of piles retaining soil behind it or are they load bearing piles taking a vertical load?

If these piles are at the shore and it is the future jetty which will provide the required draft for vessels to come alongside, why is dredging needed at all?

Obviously if you dredge to within 70mm of the toe of the pile they will not serve the intended purpose. But also I don't see why it is needed to dredge so close and deep.

If my understanding is correct then the piles should be left as is and then the additional depth for vessels will be provided from the jetty which is not yet constructed.

Or am I just confused??

 

[kieran1]

18m long piles were installed perpendicular to the shore. To support a floating jetty. My piles are located behind these piles on an arc. Some are within 1.0m of the jetty piles. I'm so worried about the piles at each end of the arc as these will be on land. Its those nearest the jetty that will be undermined by the dredging.

The jetty piles are supposed to have been designed as embedded cantilevers.

Im thinking of installing precast concrete wall sections behind the 18m piles to retain the ground behind which my piles are located.

Just need to figure out how to install these wall sections, so that when dredging commences it doesn't take the material behind the wall sections. Need to key the walls into the bed.

I'm also going to insist that all piles are tested and signed off by the piling contractor. I will not accept any liabilty for these items.

Kieran

 

[Zambo]

I'm still not sure I've completely got it.

For the new precast concrete wall sections what level will they be constructed at? (they aren't precast concrete sheet pile sections that can be driven are they?)

http://www.humeconcrete.com.my/SheetPile.html

It seems that there are solutions to your problem, such as steel sheet piles, but if you don't go significantly deeper than the dredging I can't see how you will retain the soil and protect your "short" piles.

 

[kieran1]

sorry don't have any details I can share as yet. The precast wall sections will span laterally between the jetty piles. Need to try and key these wall sections below the dredging line. If I use a 6.0m wide wall panel and key it below the dredging line by 1.0m, it should give me a minimum of 5.0m of soil behind the wall for embedment.

I will post again when I crunch some numbers and figure out how if this is buildable.

Kieran

 

[BigH]

Could you post a sketch section and plan? It might help everyone to visualize it. One wouldn't even use "zero" embedment for spread foundations unless totally on rock . . .

 

[kieran1]

Here is a plan

Kieran

 

[kieran1]

And a section including what i'm proposing

Kieran

 

[BigHarvey]

Looking at your section, you could replace the concrete panel by sheetpiles connected to your jetty piles to form a combi-wall.

 

[kieran1]

Thanks for the suggestion BigHarvey. Unfortunately we don't have any sheet piles available. Thats why i'm using the precast wall panels as we can make them on site. We have very limited resources.

Kieran

 

[Zambo]

kieran 1,

thanks for the information, it looks like an interesting, if frustrating project.

The precast wall is a good idea from a constructability point of view as you will be able install it by excavating (dredging) nearby and it will tend to sink and be guided by the piles. But I can see a few design issues. The wall has to span a considerable distance between piles, how thick will it have to be? Can the piles take the additional lateral loads? To stop the wall sections from sinking too far do they have to be connected to the piles.

To me the dredging line looks wrong. If you had the crane and clamshell bucket on your floating dock then it could dredge to the 6m depth that you require (is it 6m you need for the largest vessel to come alongside?) Then the proifile would give you the support you need for your 12m long piles. I can't really see the point of dredging up against the 18m piles when no vessel will ever be able to get close to them

 

[kieran1]

Thanks Zambo it is frustrating. I have already suggested the dredging line be moved back and the slope provided at 40 degrees this will provide at least 4.5m of embedment. I would be happy with that.

I will still provide the wall panels, if the jetty piles can resist the lateral loading. I would estimate the wall panels need to be 800mm thick. Thats alot of concrete.

Another solution would be sand bagging the front of the jetty to retain the backfill. This would be easier, but very difficult to ensure quality control. I would fill the sand bags with 50% cement.

Kieran

 

[Zambo]

For your sand bag technique first you have to agree the best possible dredging line to protect your piles. Once you have that line and associated slope in front of the 18m piles you have a few options. Sand bags are one idea, rock armour (if you have rock available from a quarry), if only smaller rocks are available perhaps you can produce gabions locally.

What length are you going to provide your added protection (be it precats concrete, sand bags or other) over. As you mention not all your piles are compromised.

 

[kieran1]

Zambo,

I have since been unable to get any information relating to the pile capacity or design etc. I find this incredible. All I've been told is they were driven to refusal. I am not taking any responsibility for the piles.

For this reason I have ruled out the precast wall idea as I cannot be sure the piles will support the lateral reactions. I thought about the gabion idea, but I cannot source any baskets or suitable stone.

I am going to cast precast concrete blocks and use them in front of the jetty piles and slope the ground behind and stabilise with sand bags. The area covered is approxiately 40m in length.
I think this will be the most practical solution with what I've got available.

Kieran