Four Tier segmental Retaining Wall w/o Geo-Grid 1

[kxa]

I originally posted this in the geotech forum but there very little traffic there!

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.

 

[kxa]

This link should work

 

[kxa]

Here is a photo:

 

[JedClampett]

If you're not an expert in segmental retaining walls, you need to get one involved. These things are pretty scary, with failures happening every year or two. The fact that yours failed, you have no Geotechnical report, nor hope of getting one activates my Spidey sense.
I couldn't view your attachments, but I don't know if it's from your end, my end or Eng-Tips end.

 

[hokie66]

Those aren't segmental retaining walls, they are just blocks stacked up 3' or 4' tall. You don't repair those. You rebuild them. Next time, do it right, and if you don't want it to lean out, lean it back while building. You could stack the blocks in front of the new wall if that look is desired.

 

[concretemasonry]

hokie is right. Those are not segmental retaining wall block (SRWs). they are just antiqued thicj paving stones meant for walkways, patios and lightly loaded driveways.

It was probably designed by a landscaper not familiar with what is needed.

Even though the heights of the individual walls are not great, a flat surface has no way to be stacked with a consistent batter that is needed, especially when water and fine soil provide lubrication for sliding.

What is needed in the end is is a real SRW (possibly a smaller size) that provides positive shear resistance (lugs or pins) and a controlled batter. There are such units that are "tumbled/antiqued" that can also have geo-grid (if needed) attached while maintaining a similar appearance. The major 4 retaining walls systems (Allan Block, Anchor Wall Systems, Keystone and Versalok) all have some units that could be used. All have run real life tests to determine the connection of the SRW to the geo-grid under wet conditions.

What has happened in one area can be expected to occur to the rest of the walls sometime in the future.

Many Geo engineers are familiar with the problems and products and even some structural engineers get involved.

Dick


Engineer and international traveler interested in construction techniques, problems and proper design.

 

[kxa]

Thanks. You are right. It was put up by a landscaper several years ago and suprisingly, it has help up this long. they kept the wall height below 4' to avoid bldg dept permit and inspection. Anyway, the client wants to maintain the plants and the look of slope. Any amount of geogrid installation could potentially result in undermining of the top tiers. Although each wall is short (under 4'), they add up to about 15' in a short distance (steep slope).

I thought about soil anchors and reinforced CMU walls starting at the bottom tier. The cost will probably be significantly less than replacing the pavers with SRW blocks and the installation of geogrid.

 

[concretemasonry]

kxa -

The arbitrary 4' (or 5' in some areas) is a simple administrative number to go by. I does not take into account the surcharge or the soil level rising above the top of the wall that usually has an effect with the magnitude depending on the soil properties.

Just replacing the units with real SRWs with shear lugs and a uniform batter may be a place to start and eliminate the excessive excavation for the geo-grid.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[RFreund]

See my response in Earth Retention forum.

EIT

http://www.HowToEngineer.com

 

[concretemasonry]

kxa - Since you are trying to do DIY repair job, all you do is to rebuild the remaining portions with more appropriate materials (SRWs with shear lugs) to extend the life of original concept.

Unfortunately, the "design"/engineering was made to easily fit the contours and provide access. With a guess at the actual slope, a SRW design and installation with 2 or 3 walls with geogrid (if necessary). Unfortunately this is not a "pick and shovel" project for an individual and equipment is required. The SRW systems that allow plantings are not adequate fot the walls heights

I have over 20 similar installations within 2 miles of me of similar heights (5 to 10'), but most of them use geo-grid for an economic solution, considering the wall curvature and varying height.

The reinforce CMU or concrete walls are not practical considering the varying heights and curvature of the walls necessary. This is exemplified by the use of high, curved walls up to 35' high of varying heights.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.