Four Tier segmental Retaining Wall w/o Geo-Grid

[kxa]

I was looking for some suggestions to repair this segmental retaining wall that was not constructed correctly in the first place. After a section of the wall collapsed, I was called to inspect it and found out that there was no geo-grid installed and now, after over ten years, there are signs of movements but mostly at the top of the walls. Plan and photo are attached.

The blocks are not the interlocking type and can even slide on each other. There is a filter fabric directly behind the wall with about a couple of inches of crushed stone.

I was thinking of using soil anchors like Manta-Ray and build a CMU wall section by section as we remove and replace the existing blocks. This way, the CMU wall and the anchor will hold back the soil and the blocks could be used as decorative facing. I also thought about gravity walls but they are big and take too much space and not practical here.

The only info I have on soil is that this was cut into a hill and it’s about 500’ from ocean. There is no way I can get boring done at the top.

Any suggestion is appreciated.

 

[kxa]

Here is the Plan & Section view.

 

[FixedEarth]

For such short walls, see if you can use a timber retaining wall just in front of the existing segmental wall with crushed gravel and subdrain between the old and the new wall.

 

[kxa]

The problem is how to make sure the lower tier can hold up the upper ones. There is not much room and don't want to use soldier piles or gravity wals.

I was wondering if anybody ever had a situation like this before. I want to see if there is a way to restrain the slope the most cost effective way and with minimum damage to the layout and plantings.

 

[FixedEarth]

kxa- based on your section the upper wall and also middle wall are not surcharging the lower wall. I had similar job earlier this year. They had CMU wall but it was failing in sliding. So we added a 3 ft deep keyway at the toe.

You need to ask the soils firm to check the global and surficial soil slope stability and to provide geotechnical criteria for your new wall. This way we get to fix it one time. I agree, this existing wall - it is a miracle it stood this long. Other alternatives include Rubble wall and Geogrid wall.

 

[kxa]

Thanks for your input. I will try to get a geotech engineer involved. Just wondering, how did you put a 3' keyway in front of an existing CMU wall that was failing in sliding.

 

[FixedEarth]

The calculated F.S. against sliding was less than 1.50 but the retaining wall has not "failed".

 

[dcarr82775]

The plan shows the tiers get very close together, but your photo and sketch shows the tiers far apart. If the walls do get as close as the plan shows the lower tiers will certainly see the surcharge of the upper ones.

 

[RFreund]

I agree that if the walls are 11' or more apart and only 4' tall then they don't seem to be influencing each other. You can double check this with NCMA's design manual for segmental walls (Approximate tier surcharge). I would replace with Keystone Standard units (about 20" deep). It looks like for the heights and slopes, they should work. Although double check this. It is a gravity segmental wall system and seems like an economical replacement with out having to excavate and put in grid. However if they don't mind the excavation, have your choice with a grided wall system.

EIT

http://www.HowToEngineer.com

 

[aeoliantexan]

Walls like this won't meet standards, but they usually deteriorate slowly. When they collapse, water is usually involved. Your photo seems to indicate that the fabric is against the wall and the gravel behind the fabric. The fabric should be between the soil and the gravel. The soil may have moved through the gravel and clogged the fabric; then the wall tried to hold water during a heavy rain. A poor footing may also have contributed.

The section indicates an overall slope of about 3H:1V. The soil might be stable without walls, just grade it and put the sod back. Sell the salvaged stone.

You may be able to make the stone you have work by battering the walls into the slope. You will need a good footing, wider gravel zone with the fabric in the right place, and surface drainage that does not trap water behind the wall.

I agree, you need a geotech. Tell him to bring a hand auger.