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Commercial job, question about securing a cut next to a parking area

joispoi

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Mar 1, 2008
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I looked at a job for one of my customers this morning. The objective is to add more loading docks to a shipping warehouse. The work involved requires removing 5 bays from their current locations and then installing 12 new bays. That's the straight forward part

There's nothing particularly complicated about it, but there's an area that I need to dig out next to a recently paved parking lot. The soil is sandy and I don't have enough room to slope back the face of the cut between where I have to put in a new footing and the parking area that's about 4 feet higher and right up against the cut.

20140705_093214[1].jpg

The wall in the picture needs to slide 3 feet to the left. The parking area above was recently paved and must be conserved.

What's my best option for stabilizing the cut so that the bank doesn't collapse and damage the asphalt? The soil is pretty much pure sand. There's about 60 feet of wall to replace. It's around 4 feet at the lowest point and comes up to grade at the top of the ramp as can be seen in the picture.

I'm not set up for sheet piling. The biggest machine I have is a 5 ton mini.

One idea that comes to mind is lime injection soil stabilization before I dig. Has anybody tried this approach or have a different idea?
 

oceanobob

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Hopscotch, Blindside Forming, judicious use of water jetting, etc come to mind.
Shoring using temp posts then excavate and place backing between.

Can you use the existing wall as a brace point?

Lime needs to react, but you've indicated sandy soil. Never had luck with that combo but you can get cement to function.

We have observed pics on the web showing folks using helical anchors as temp pilings to accomplish this but have not found one mfg that will validate the use.

More finicky techniques at the three and four foot deep area .... four feet finished could become five plus feet to put concrete footing below the final surface.

What is your plan for the permanent wall restraint - a standard mass footing or drilled shaft?

Definitely get an engineer's point of view so you don't underestimate the forces; sometimes all that is available is the finished retaining wall design and the contractor has to seek additional sage.
 

mitch504

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Andrews SC
Sheet piling was going to be my answer, but, you killed that for me. :mad:

Here's a wild idea that probably won't work, but maybe thinking about it will give you an idea.
What if you dug along the line of the new wall with a trencher, put a plywood form on the good side, and then pour the new wall in place, with anchors as necessary.
 

CM1995

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Are they going to asphalt the 3' area in the lower section after the wall is built? Considering the options and associated expense of underpinning the upper parking lot, it may be cheaper in the end to saw cut 4-5' of the upper asphalt, remove it in order to get a slope that will stay there and then re-lay the asphalt if they are going to pave the lower section.

I read where you stated the upper parking area must be preserved but with all options weighed, may be the cheapest route to remove some of it.
 

oceanobob

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Maybe the upper a/c must remain in place for truck access?
This need to have heavy loads w transient passing at the edge of an excavation is the type of job I always seem to be faced with....
 

pondo

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Hi, I know u said not set up for sheet pile but since it's sand why not just post pounder and drive/pound a continuous wall of sq posts 4x4 or if really concerned make them 6x6...could add some horizontal posts, bolting them to the vertical for extra strength where wall get over 2ft.
But u get the idea. Then u would have finished retaining wall when done.
 

old-iron-habit

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You might be able to drive H beams down with the hoe bucket, then lag them with rough cut 2 x10 or 2x 12 as you dig. Fill behind the lagging if it shuffles away. Best way to lag them is to weld corse thread bolts to the front(digging side) of the H beam and using a plate washer simply add lagging as you dig each foot. Try to get the H beams down 9 to 10 ft if you are excavating 5. With 2x12 you should be able to space the soldier pile at 8 ft and get by with a 8" H beam. You can get shorter as the excavation gets shallower.
 

Red Roan

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I must admit, I like CM's ideal of just cutting back the parking lot & rebuilding it. You said the soil was " Sandy". I'd have to see just how " Sandy " it was before offering up an alternate.

If it were me, I'd use pre cast concrete blocks to make the wall out of. Have the blocks sitting there, and as soon as you make a few pulls with the Hoe & get it on grade, lay a couple of blocks in before the sand makes up it's mind to slide down. I've done a handful of stream restoration projects with these blocks. They are cheap, easy to work with, and don't look too bad either. They come in a few different sizes, and once they are set, they ain't goin anywhere.

And as a capper, I'd backfill the little bit of overdig with flowable fill up to within 6" - 8" of grade.

All depends just how slippery that sand wants to be, but if it were me, I'd certainly be willing to try that option before getting into underpinng , or any other types of shoring.
 

buckfever

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I have done something like this in the past like old-iron-habit said. Drive H-beams into the ground at 8 foot centers. Then trench between the post and slide 6 x6's to make a temp wall or if the owner will agree use precast concrete panels and just make that the permanent wall.

If your worried about pounding the post in contact a local guard rail install company. They can pound the post in and pull them out when you are done.
 

joispoi

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All good ideas so far, guys. Thanks.

I think CM is right on this one. The work required to try to save the asphalt isn't going to be justifiable. The customer is pretty objective when it comes to ROI so I think he'll understand when I show him some numbers. I think the best solution is going to be to put a CYA clause in contract stating that the asphalt may have to be replaced at an additional cost. I can probably get away with digging it out and then driving some I beams on 10 foot centers and then adding form boards in between them. I only have to dig down about 5 feet measuring from the top of the wall so there isn't going to be much pressure on the shoring.
 

CM1995

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The work required to try to save the asphalt isn't going to be justifiable

No it's not. One of the biggest expenses on a small job is mobilization with a paving crew, adding 10 tons or so of hot mix is a much lower cost compared to installing and removing shoring. They can do that in a day easily.

Since the excavation is shallow and the wall height is only 4', it's the most economical way to go. Who knows, you may not have to remove the upper asphalt at all, you'll find out once you start excavating.

Another option if the material does slough off and undermines the upper asphalt, once the wall is built use flowable fill or lean concrete as backfill which would support any undermined areas of the upper parking lot. Still much cheaper than shoring.
 

tylermckee

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I like the idea of using something like a redirock block retaining wall, since it's only 60'x4' you can excavate and have the wall rebuilt in one day. With a little luck the sand won't sluff off too much and you'll be done. Plus side is they look better than a poured wall IMOimage.jpg
 

RBMcCloskey

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Support of Excavation

I suggest you install H-Piles and Lagging. I would suggest a W10 x 60 section spaced at 5.0' o/c @ 15.0' each, based on a cantilever of 2 to 1; 5.0' exposed and 10.0' buried. Lagging use 3" x 12" Oak.

1) Drill holes using truck mounted auger, fill the hole with water and bentonite to support the hole, set the H-Pile and backfill the hole with 2,000 psi concrete.
2) Excavate and lag, slope the excavation away from the H-Piles and hand dig at the beam flanges to set the lags, set the lags against the inside front flange, back pack the lags with hay to prevent soil loss and space the lags +/- 1/4" this allows and water that accumulates behind the lagging to drain.
3) Cut off the H-Piles to grade.
4) Install a fence or plantings along the top of the wall, yes they will drive off the wall without a barrier.
5) Have design checked and approved by a Professional Engineer.
 
Last edited:

dozerman400

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12' long 4x4's make a point at one end, drive them in with the hoe every 3' or so. Put some plywood 4'x8' sheets down the long way so each piece is behind three 4'x4's. Need to dig a little, push down on plywood, backfill plywood as you go. I have done this in clay, sand and more. If you hit rocks or garbage material this can be a head ache. Check plywood for any leaning in, may have to put more 4'x4''s.

You may have to adjust this some. I don't have an engineering degree, but I have dug a lot of holes in tight places with this method.

Be safe, if it don't look right, it probably is not.

I would try some kind of shoring, neighbors can be difficult with patch jobs.
 

joispoi

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I haven't checked on this thread in a while. A lot of very good replies here. This job is not going to happen.

Thanks for the input.
 
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