Steel Pile Friction

[mudcatwilly]

I am designing a temporary retaining wall consisting of steel soldier piles and wood lagging. The wall will have to be removed, so I am planning to set the steel piles in drilled holes about 16 feet bgs and then backfill the holes around the piles with class 2 base rock. To remove the piles, I want to use a large excavator and lift them out of the gravel filled holes. What do you think is a suitable friction force to use in order to calculate the required force that will be required of the excavator to lift the piles out of the holes?

These will be W12x50 piles, 22 feet long (16 feet bgs) set in 18-inch diameter holes. The excavator will be able to sit on relatively flat ground at a close distance to lift the piles out. With those parameters, the excavator can lift about 20k vertically.

 

[dcarr82775]

How do you plan on compacting the fill around the pile? It needs to be dense so that the pile can push against it for passive pressures. We once had a contractor change our design without our knowledge and do something similar to what you described. The wall moved a lot and had to be braced internally to prevent undermining the house behind the cut. Requiring the wall to be removed makes things difficult, but I would stay away from what you propose. Just my 2 cents.

 

[DRC1]

I would expect 10-20 tons in sand for resistance. If you use a small vibrator suspended from the backhoe, they will come out easily. Vibrator will not produce a lot of vibration.

 

[mudcatwilly]

In response to the concern about wall deflection, I'm not worried about that. The purpose of the temporary wall is to create a shoulder along an existing narrow roadway that is cut into a steep slope. We want the shoulder so we can sit on it and drill below the road without completely shutting down the road. We just need it as a temporary construction platform in order to build a much larger wall below it.

 

[PEinc]

What will prevent the Class 2 base rock from running out from around the soldier beam when you excavate to install the lagging? Instead of loose base course stone, use LOW STRENGHT, flowable fill (about 100 psi). You may need to vibrate the soldiers to get them out.

Usually, the soldier beams are cut off about 3 or 4 feet below finished grade with the rest of the system being abandoned in place. Full removal can sometimes cause voids and settlement problems.

http://www.PeirceEngineering.com

 

[mudcatwilly]

The base rock will only be added to the holes up until the bottom of the exposed wall elevation. The temporary wall is being installed on a down slope, so the soldier piles will be sticking out of the ground when we install the lagging. Then we will add compacted fill behind the wall to build the drilling platform. The reason we have to remove the wall is because it is a highly environmentally sensitive sight and the owner (government) does not want any buried structures left behind.

Again, the only question I have is how much friction to use in my calculations to pull the piles out of the ground. I don't care if the wall deflects an inch or two. When we build the big wall below the temporary wall, all of the soil will end up getting reworked and compacted. The only thing that will remain are the holes filled with base rock.

 

[VAD]

Mudcatwilly:

Just a thought looking at the ease of removal of piles first. I presume that in reoving the piles you would first remove the backfill against the wall, then the lagging. Could you use a hydovac truck to remove the stone fill from the pile holes. At least some can be removed by this process and allow you to use less force in removing the H-piles.

Alternatively the brute force approach would require you to calculate the frictional resistance afforded by the gravel on the pile. Friction values of stone against steel are available in the literature or some close assumption can be used, and as well one needs to add the weight of the pile and stone, and some frictional resistance of the stone against the excavated pile hole. Pouring some water down the pile holes can possibly assist in friction reduction.

Nice problem to play around with numbers and concepts

 

[Brad805]

I think it will require a much larger excavator or a crane. If you use something like 500psf, the forces seems to be in the 40k range. I have seen allowable shaft frictional values equal to 500psf in gravels, so the force could be far greater. Plus none of those values take into account what is going to happen when the wall is loaded, deforms, and presses some of the rock into the drilled shaft. If the client has made it mandatory these be removed, and this is the best solution, I think you need to conduct a mock up test. We have tried removing old piles in the past, and most of the time you wind up breaking and bending things before you make any progress. I doubt you will find many contractors to give you a guarantee or fixed price to remove them if there is a large quantity of these. He could end up in the poor house if the removal goes badly.

Another way to look at it is from a pile driving standpoint. If it takes a 5000lb hammer dropping 8ft to drive a pile that last 2", how much do you think it will take to get pull it out? The trick is getting the pile to start pulling out.

Brad

 

[aeoliantexan]

A contractor I know told me he does this regularly. At the time we were discussing an excavation into shale. He does a lot of big pipeline work and has very large traxcavators; so I am guessing he pulls them with those.

 

[DRC1]

Pulling piles in clays is significantly easier than pulling piles in stone. Again the best way to do this is to use a vibratory driver/extractor. I would not recomend pulling with a crane,unless you are using a vibratory extractor.

 

[PSlem]

You might try this sleeve or their coating which are designed to reduce downdrag in fill applications.

http://www.foundationtechnologies.com/Yellow-Jacket.php

 

[PilebuckEngineer]

Just pulled some hp 14x117 soldier piles today filled with cdf. We woke them up with a 4400 in lb hammer then puled them. The trick is to take them down first, which breaks the skin fricton, then pull them up. The lagging will be a lost cause...

 

[PEinc]

Interesting. Thanks, PilebuckEngineer.

http://www.PeirceEngineering.com