Wall Construction

[LC06]

Hello,

I'm a Civil/Site Engineer and I'm currently dealing with the permitting process for a residential subdivision. The access road to the subdivision requires a 30-foot high retaining wall to be constructed in a cut. The soils are very course sand overlaying course gravely sand. The problem I've ran into is that I'm not sure how to generally construct this wall. How would the excavation be stabilized? Would sheeting be used? Shoring? The cons. comm. does want some sort general explanation. Any thoughts? I've attached a cross-section.

Thanks!

 

[MTPipeliner]

It may be helpful if you talk to a construction contractor in the area to get their opinion about how to approach it. I think there are several ways to accomplish it.

The first idea that came to my mind is to overexcavate behind the wall then fill it in and compact as you build the wall.

 

[civilperson]

Drill holes for auger cast piles and use top down construction.

 

[cvg]

30 foot high shoring will probably cost you around $50 per square foot which is $1,500 per linear foot just to construct the shoring system. At that point you may as well just build a concrete facing and leave the shoring in place. Another option is to excavate the 30 feet and lay it back at 1:1 or flatter depending on your safe angle of repose. If you do that, you may want to step your wall back so you don't have to backfill as much.

 

[born2drill]

There are many different ways to do what you're proposing. If you have the room to lay the soil back with an open cut then build up your MSE wall it will probably be cheapest. But that will require you to slope a long way from the back of the geogrids up to existing grade. I don't know if you have that kind of room.

It usually doesn't make sense to build a top-down wall only to place a bottom-up one in front of it. As others mentioned above, soldier beam and lagging or soil nail walls can be used for permanent applications.

As for price, it will vary greatly depending on the size of the job, subsurface conditions, access, location, and whether union or open shop labor is used. It may end up being a little cheaper than cvg's $50/sf. It may end up being a whole lot more...

 

[Drumchaser]

LC06

No expert here. But I will try to help.

Has the block wall "system" been designed yet? If so you should have strap length and locations of lengths for a given height of wall (hW). This will give you the actual work excav. limits required to construct the wall. And maybe this has been done and your sections are to scale.

I think you are going to need some geotechnical data on the soils of your cut.

I would use the sheet pile, make the cut, then build the wall, place fill in area between proposed top of wall and behind sheet face, place top soil and establish good vegetative in this area, remove the sheets.

 

[PEinc]

LC06,

Call Moretrench in Assonet, MA and Schnabel Foundation Company in Southborough, MA. They may be local and can give you design-build proposals for a permanently tiedback or soil nailed wall.

 

[oldestguy]

One more thought:

That's a pretty high wall for one to design if he has not done that much before. I'd let someone else take responsibility for it, specifically an experienced contractor

Sometimes for public type work you might just bid the idea with the final result specified as to the wall dimensions and location. Then, require the contractor to design and build it at his fixed price with a guarantee as to structurally capability. That way you don't design or take responsibility for it, since that is not your expertise. Of course require the designer to be fully licensed,etc.

The types of firms mentioned above are the kind you should use with provided evidence of past similar work. This way you get the wall you want at lowest cost.

 

[LCruiser]

I agree with born2drill. Soil Nails or permanent soldier piles. You might leave it to a design build contractor though. Depending on where you are a local contractor of one kind or another might have significantly lower mobilization costs. It's a small wall, leave it up to the market...

 

[born2drill]

Just remember, LCruiser - you get what you pay for. Watch out for cheap prices from contractors who are in over their heads. PEinc named two excellent companies. (one being my former employer)

If LC06 let us know where this project is, many of us here could get him in touch with the right people in his area....

 

[Drumchaser]

LC

if I were the owner, there would be a Mech Stab Earth wall (like you see on highway projects) the block wall (my opinion only) is only for 6-7 foot heights.

I have seen others build them 30 ft high. I would not. Several potential issues. $$$$$, maint., closely monitoring.

 

[davep043]

I'm with several others here, I'd look for design-build services, with either soil nail or soldier-pile and permanent tiebacks. A cast-in-place permanent facing can be used with soldier piles, while soil nailing more often uses a gunnite facing. With clean sands and gravel, there may be difficulties either way in maintaining short-term stability of the cut face. Excavation support contractors can provide some details as to how they'd handle it.

 

[eea]

Solider pile or sheet pile would be my initial considerations. Assuming aesthetics aren't an issue, my experience is that a high section modulus cantilevered sheetpile would go quicker during construction. If your preliminary design crests over into tie backs, I'd look at solider pile. I had Schnabel on a solider pile project, no faults except they kept pushing for high strength tie backs to increase spacing & reduce # of piles. One might call it value engineering, another might call it reducing your factor of safety.

 

[fattdad]

I'd go design build. Wish what you want on paper (i.e., top of wall, bottom of wall, grades,etc.) and have the contractor submit sealed design drawings and have the onus to put it in place.

Bear in mind that if you are cutting close the property line, the availability of a construction easement may allow for greater options in the contractor's approach.

f-d

¡papá gordo ain’t no madre flaca!

 

[PEinc]

IMHO, 30 feet is too high to consider cantilevered sheet piling. It could be quicker but it would be very heavy, very long, very expensive, and would probably deflect too much (unless, again, it is even longer, heasvier, more expensive).

As I said before, call Moretrench and/or Schnabel for a design build proposal.

Also, "high strength tie backs to increase spacing & reduce # of piles" does not reduce the safety factor. This statement is more likely to indicate limited tiedback wall experience from anyone who believes the statement.

 

[born2drill]

Right. Fewer tiebacks with higher capacity will in most cases be cheaper and faster, but certainly no less safe. Ground anchors are one of the most reliable construction techniques out there. Remember every one is tested!

Also, the necessity for tiebacks isn't what determines whether you use sheets or beams.

 

[chicopee]

Looking at your worksheet, it appears that the design is with doublwall. If you are from the North East, contact Atlantic Pipe Corp in Plainville,Ct since they design and build such retaining walls. Doublewall is an excellent product.

 

[PEinc]

It doesn't matter if the wall was originally designed for Doublewall. You would still need another temporary sheeting wall to build the doublewall. Therefore, the originally designed wall is not economical.

 

[jlewis1002]

Give you another thought on your wall. You might want to look at doing a secant pile wall. Then you can design the strength you need for minimizing the tie-backs with the use of either HD beams or extra rebar in your columns. The other replys are right, get an experienced contractor. Moretrench and Schnabel are both good. You might also look at Remedial Construction Services, (RECON) out of Houton Texas also. They have offices all over the U.S. now. I'm sure they can cover you where your at.

 

[born2drill]

I'm not sure why everyone is so in love with the secant pile wall lately, but I'd venture to say that a secant wall will be way beyond the budget for temporary earth retention on a residential subdivision.