Emergency Retaining Wall with Stream at Toe 4

[cpkuehn33]

A municipality has recently reached out with an emergency project. A slope directly adjacent to an existing road is showing serious signs of instability. The problem area is approximately 40 feet in length (along face of wall) and a maximum height of 20 feet. I mainly design temporary and permanent anchor earth retention systems (i.e. tiebacks, soil nails, helicals, etc.) however the wrinkle in this project is the road is directly tangent to a curve in a stream at this location.

I'm still in the fact gathering stage of this project, but from what I've seen the existing soil slope appears to be at a 2V:1H slope. We're collecting survey data and geotechnical borings now, but the municipality would like the road geometry and stream geometry to remain unchanged. So my first thought was sheet piles, however in the pictures I've been sent the stream bed appears to be rock and/or boulders.

So my question is if a sheet pile wall won't work due to constructability, and an MSE system won't work due to existing geometries is there a way to mitigate scour concerns using either a soil nail wall or soldier pile will? I know GEC 7 essentially says alternate systems should be considered if scour is a factor for traditional soil nail walls, and I haven't found anything in GEC 4 addressing scour. I myself am still researching any publications which would address this issue, but figured I would ask here concurrently.

As always, any help is appreciated.

Thanks.

 

[GeoEnvGuy]

O piles

 

[BigH]

Can you post some pictures? They always help.

 

[cpkuehn33]

Pictures attached.

GeoEnvG I'm not that familiar with O-Piles, but they seem like they would be cost prohibitive for a project of this size. I'll reach out to the manufacturer though for some budgetary numbers.

 

[Mad Mike]

I would envisage a soil-nailed wall to support the soil face below the road, and then some scour-protection at the immediate base of this. A tight stone packing (rip-rap) might suffice for the latter, but would have to be inspected/maintained after storms. Try squeeze in a line of gabions...

All the best,
Mike

 

[cpkuehn33]

Mad Mike, that's also where my thoughts went initially. I was considering taking nails down to bottom of stream and extending filter fabric and rip-rap to 24" below current bottom of stream. The stream isn't very deep currently, probably 3-4 feet at wall face.

I was hoping somebody has done something like this before to confirm my concept, since I typically see gabion walls used for this sort of thing traditionally.

 

[Mad Mike]

I'm familiar enough with the soil-nailed wall component- I haven't installed one in this situation before so could not give the details of the interface between wall and rip-rap. As with you, I've always looked to gabions in this situation.

My feeling is that your proposal is spot on, but wait for others to comment.

Cheers,
Mike

 

[oldestguy]

I'd look at a bunch or rip-rap and be done with it.

 

[MTNClimber]

I agree with OG, if the regulators will allow it.

 

[cpkuehn33]

Unfortunately rip rap won't work without changing the stream "path". The municipality is worried about the permitting time delays, so they're trying to look at some other options.

 

[PEinc]

Whatever you do will be at least partly into the creek and will require permitting.

http://www.PeirceEngineering.com

 

[JAE]

How about some gravity blocks - like Stone Strong?

 

[oldestguy]

This is an emergency and waiting for permits can have half the side of the road in the creek.

 

[r13]

Quite assertive !

 

[PEinc]

Yeah, keep telling that to Maryland DNR.

http://www.PeirceEngineering.com

 

[oldestguy]

How ya gunna do that when the office is empty and the folks are home watching a soap opera?

 

[r13]

Maybe provide temporary erosion fabric with a few rock layers along the bank, and wait for the final word on permanent solution.

 

[cvg]

soil nail, shotcrete facing and extend the shotcrete below the ground as far as possible. backfill the trench with riprap. since it is 2:1 slope, can you shotcrete without the nails? is there seepage from uphill?

 

[Obregon]

An Anchored Gabion Wall will do it.

 

[miningman]

Prepare a proposal..technically valid , even if a bit expensive. Submit it to the AHJ and wait for their response. If the road slides into the creek while waiting for their response, who cares?? It might focus their attention in the future. It looks as tho there is lots oaf room to move the course of the stream once authorization has been granted