Sliding a landscape foundation wall to the intended location 2

[RHTPE]

One of my contractor clients has decided to attempt to "slide" a incorrectly located retaining wall to its desired location.

My task is focused more on the mechanics of the "slide" and the steps involved. I have seen this done with pad footings for interior columns but never for a retaining wall and its footing. The cost:benefit analysis is my client's problem, not mine.

I expect that the footing sits on compacted processed gravel. The wall is about 6 feet tall. The heavy equipment is available to tug on the wall. I would expect to connect to the footing (rather than the wall) so that the wall does not topple over. Obviously I have to consider the rigging and its geometry and the forces involved so that no one component is undersized.

My questions for the group:
- Has anyone been through something similar?
- What coefficient of friction might be a good guess so I can estimate the required force to slide the assembly?

It need not be said that demolishing and rebuilding the footing & wall might still be in the cards should the move prove to be unsuccessful. If it works, my client saves a bundle. If it doesn't, he hasn't invested a lot in the attempt.


Ralph
Structures Consulting
Northeast USA

 

[oldestguy]

My experience was with moving foundation, fixing the ground and moving back. Just make sure the machine is big enough. For a wall, I'd cut into sections and move each to avoid breaking it in half. For friction consider an angle of friction of at least 30 for loose material, possibly as high as 36 degrees. If some how cemented material 45 degrees would be possible, but very unlikely.

 

[GeoPaveTraffic]

I agree with oldestguy.

Depends on the material below the wall footing and how the wall was constructed.

I wish him the best of luck. I expect that the forces involved are way higher than he expects and that he will break a lot of cables and/or equipment trying to move the wall.

Mike Lambert

 

[Lomarandil]

Similar to Oldestguy's suggestion, Caltrans publishes a friction factor of 0.6 for concrete set on dry gravel, so I'd suspect the ultimate value is higher than that.

 

[Ron]

You might consider some instrumentation on the wall and the footing to determine the real-time stresses and tilting.

 

[RHTPE]

Good idea Ron. More thoughts on that later (I do not have the resources for sophisticated instrumentation).

See the attachment for a plan sketch. Overall length of wall is 36'. Footing is continuous under expansion joints.

What we're considering as of today:
[li]1. Wait for appropriate weather. Right now we have sub-zero possibilities. Footing & one wall face have been partially backfilled.[/li]
[li]2. We will likely use a large excavator, positioned so that the bucket will be against the farside of the wall, and pull the wall towards the machine.[/li]
[li]2a. The bucket will contact the side of the footing at mid-footing thickness with some timber crush material between the cutting edge and the footing.[/li]
[li]3. The footing has T & B longitudinal bars so we can consider it to be a beam lying on its side on the ground.[/li]
[li]4. The footing at the pivot point has to be cut to permit the assembly to pivot. Dowels into the straight wall to remain as-is could be the 'hinges'. Might add back-up members at the pivot point to help as hinges.[/li]
[li]5. Now, the fun part - determine where to apply force to the wall so that it slides in the desired direction.[/li]

Should be a fun exercise. Any more thoughts out there?



Ralph
Structures Consulting
Northeast USA

 

[dirtsqueezer]

You might want to make sure those 30 day breaks have come in, too. Best of luck, there, cowboy.

 

[oldestguy]

I'd set some stakes ahead of the move direction, showing where it should stop, in case there is some flexing of it. If there was the possibility, a group of workers, each in an excavation in the back side, each with a hand powered jack could move it in a more controlled manner than with one push on one place.

 

[RHTPE]

dirtsqueezer - I'm not too concerned above concrete strength, but you point is valid and I will request the 28 day breaks.

oldestguy - I would be inclined to agree with your thinking, but I am forced to work with what my client has at his disposal. We are moving the wall towards the retained side, so any partial backfill has to be removed down to bottom of footing elevation. Before the slide the base will have to be compacted and the grade trimmed so we're not 'plowing' dirt any more than necessary.

I get the fun stuff from contractors. Just wish it were vastly more profitable.


Ralph
Structures Consulting
Northeast USA

 

[KootK]

Your retaining wall is barely a retaining wall at all in terms of proportions. With a footing that narrow, I expect you'll have a very difficult time keeping the thing from flopping over. Here's another, Flintstone-ish, idea:

1) Cut the footing as required to divide the wall into chunks.

2) At the ends of each segment, core a hole in the wall safely above the centre of gravity.

3) Do whatever rigging voodo you gotta do to set up the holes at the wall ends as lifting/sling points.

4) Pull the excavator up close to one of the wall ends and lift it by the rigging.

5) Switch from side to side and walk the wall into position.

Concerns:

1) Excavator lifting capacity
2) General safety.
3) Getting wall segments to line up well after the move.




I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[dicksewerrat]

Is the 10 inches only at the end of the second 18 ft. arc? and is the 'pivot point where you will saw cut and patch when all is done? I would find out how much this will cost and what anew wall will cost. then go to the owner and negotiate some kind of deal for acceptance. You are only talking about a small are gained by moving the wall.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[aeoliantexan]

I think you can probably do what you are planning. I agree that the coefficient of friction on the sand may be higher than expected.

Let me suggest a completely different approach:
Separate the part of the wall to be moved from the part to remain.
Dig 3 or 4 trenches under the footing, oriented in the direction you want to move it. Say at least 2 feet wide, 6 feet long, 1.5 feet deep.
Lay two 6" by 12" hardwood timbers in each trench. One of each pair must have a planed surface.
Set 2 jacks on the rough timber of each pair and raise the wall about 3 inches.
Lay another timber on each of the non-loaded timbers, planed surface down. First, though, smear grease generously on the surfaces that will come together.
Set the wall down on the greased timbers.
Bolt a husky wooden block or piece of steel angle to one end of each of the bottom timbers.
Place jacks horizontally between the end of each upper timber and the block and move the wall with the jacks.

This will take longer than your plan, but you can have better control, a better chance of ending just where you want, and reduced risk.

 

[RHTPE]

aeoliantexan - I like your idea, BUT I suspect the footing bears on compacted, somewhat coarse, processed gravel, not sand. The footing is not going to have a relatively smooth bottom, so if it's lifted, slid, and lowered, it's not necessarily going to settle back down to its original elevation because of the irregularities. It may also leave it prone to some additional settlement over time. One end of the wall butts up to another wall that will remain, so elevation control is important. Both sides of all walls get a stone veneer with minimal tolerance, so plumbness and elevation will be important.

By sliding it on the compacted gravel I think that any "outie" irregularities will simply plow through the gravel, and the entire footing + wall will not change elevation.

What concerns me is the lack of control. It will take substantial force to start it moving and getting it to stop precisely where it should requires some additional thought. I have been thinking of positioning some precast traffic barriers or concrete deadmen (perpendicular to the wall) so that their ends are on the line where things should be. Hopefully they will have enough mass to act as a stop.


Ralph
Structures Consulting
Northeast USA

 

[oldestguy]

RHTPE:

It sure is an interesting problem. A few thoughts. Suppose it does not stop exactly where you want and also suppose the the exact shape (an arc?) is not repeated. Will anyone know or care? Assuming a back-hoe bucket is the pusher, can you work it out that it finally "wiggles" the wall back and forth in case the rough support soil leaves it a little high at a location where it matters?

 

[aeoliantexan]

RHTPE:
I suppose you could dish the proposed bearing location, fill it with fluid concrete, lower the footing to the desired elevation, and leave it on the jacks until the concrete sets.

 

[RHTPE]

Sorry about the delay in reporting the final outcome.

Once my client realized the prep work require for the methodology that I developed, he decided to demolish and reconstruct.

Probably a more realistic outcome than trying to slide/rotate the footing + wall to the correct location.


Ralph
Structures Consulting
Northeast USA

 

[KootK]

Reason prevails! Thanks for the update.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Ron]

Thanks for the follow up, Ralph.

 

[racookpe1978]

Shucks. At -30 degrees, I was going to go the opposite way, and recommend sliding it on an ice-filled level surface back towards the embankment. Now, that leaves you the problem of getting rid of the ice/water/mud melt after the move completes, but should be little more difficult than a water-mud "pond" behind a retaining wall after melting/building during the summer.

 

[RHTPE]

racookpe1978 - I was kinda hopeful he'd give it a go so I could find out if my guesstimation of where to apply the force, and in what direction the force should act, would indeed slide/rotate the wall correctly. Kind of an Archimedes thing. With the least amount of damage to the wall in the process, of course.

With this client, there will be another opportunity to correct an "oops".

Keeps my involvement in our craft interesting.



Ralph
Structures Consulting
Northeast USA