×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Four Tier segmental Retaining Wall w/o Geo-Grid

Four Tier segmental Retaining Wall w/o Geo-Grid

Four Tier segmental Retaining Wall w/o Geo-Grid

(OP)
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.

RE: Four Tier segmental Retaining Wall w/o Geo-Grid

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.

RE: Four Tier segmental Retaining Wall w/o Geo-Grid

(OP)
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.

RE: Four Tier segmental Retaining Wall w/o Geo-Grid

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.

RE: Four Tier segmental Retaining Wall w/o Geo-Grid

(OP)
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.

RE: Four Tier segmental Retaining Wall w/o Geo-Grid

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

RE: Four Tier segmental Retaining Wall w/o Geo-Grid

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.

RE: Four Tier segmental Retaining Wall w/o Geo-Grid

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
www.HowToEngineer.com

RE: Four Tier segmental Retaining Wall w/o Geo-Grid

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.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources