Repair of Segmental Block Retaining Wall

[eric1037]

I am working on a project that involves a contractor that constructed a segmental block retaining wall (Rockwood Classic 6 block) without the benefit of engineering.

Consequently, the wall is now starting to overturn and/or slide.

I am trying to come up with some different alternatives for stabilizing the wall. We are constrained because a house is located about 6 to 8 feet from the face of the wall. There is a 32 degree slope at the top of the wall. There is very limited access.

To complicate matters futher, we are about 15 feet from the property line. The wall is retaining relatively clean sand.

Therefore, tearing down the wall and starting over will have to be accomplished using hand excavation methods. With the slope as steep as it is, I believe the sand would cave and it would be a nightmare to deal with.

I am considering some type of tieback system including soil nailing, helical anchors, etc., but I am not sure how to anchor to the wall since it is mortarless and the blocks are practically independant. I have considered using whalers and anchoring to those.

I have also consider dismantling part of the wall and using h-piles to anchor the geogrid back.

I guess I am looking for additional input from people who have had experience with this type of situation. Is there any other way to stabilize the wall that I haven't considered?

Thanks in advance!

 

[bridgebuster]

Last week I attended a lecture on this subject, given by Professor Robert Koerner of Drexel University.

Soil nailing and shotcrete is a common remedy as well as rebuilding the wall.

Remember one thing - drainage is critical.

 

[PEinc]

Soil nailing a clean sand with grouted nails may be somewhat more difficult than nailing a more cohesive soil. The nail drill holes may need to be cased to prevent their collapse. This can be more expensive and require larger drilling equipment for your tight work area. You may be able to install small diameter helical soil nails by removing isolated blocks. After the nails are in, you could attach a new facing (shotcrete? Boulder Scape?) over the front of the block wall. The helical nails could damage the geogrids (less so if installed horizontally between grid layers).

I'm sure the Koerner lecture was as informative as it was entertaining! He's "The Man."

 

[MSEMan]

I would be worried that with only 6-8 ft of space in front of the wall you won't be able to get a rig in for anchoring or drilling.

A lot depends on the geometry and the ability of the sand to cut in a temporary condition but - have you thought about cutting the surcharge slope back and constructing another wall (or series of walls)at higher level offset horizontally from the existing? Since you will be reducing the net surcharge, overturning and sliding forces will be reduced (of course you will also reduce the resistance to sliding)and the resultant of the horizontal forces will be more favourable. You will want to found these walls as deeply as possibly to minimise the forces acting on the existing wall. This is sort of an engineer the loads rather than the wall approach.

 

[eric1037]

Thanks for all of the input so far.

After some discussions with specialty contractors, I am finding that it is more economical to dismantel and rebuild the wall due to the small size of the wall. It is only about 75 feet long. I am considering a tiered wall system to reduce the disturbance to the slope.

I have attached a drawing of the situation. I thought it may help things.

 

[valleyboy]

Would it be possible to grout the existing wall from above to solidify the existing backfill, thus forming a mass retaining wall which would be adequate to resist the horizontal forces?

Just a thought.

 

[PSlem]

How will you excavate back far enough to install longer geogrid without supporting the cut or encroaching on the neighboring property? What are the consequences of a slip failure? I would fix this with helical anchors and shotcrete.