×
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

Retaining Wall Review

Retaining Wall Review

Retaining Wall Review

(OP)
Hi,

I'm doing a design review for the stabilisation of a 30 foot cut face. The slope of the land beyond the face is fairly steep at 27-30 degrees. The topsoil layer is about 3 feet thick but the rest of the face appears to be cemented granular material of varying consistency. See attached picture. The engineer has proposed a 20 foot high masonry retaining wall and the final 10 feet, has proposed a geomat. The engineer has also specified 1% cement by volume to the backfill and the width of the backfill zone varies between 3-6 feet. The design looks very lean to me and the only way I can say the wall works is if the cement stabilized backfill lowers the active pressure on the wall significantly and if they have determined that the cut face is stable and full active wedge is not developed. What friction angle would one consider for the backfill described below?

crushed stone + 1% cement by volume
sand + 1% cement by volume
coarse grained gravelly/sandy soil + 1% cement by volume

Thanks

RE: Retaining Wall Review

What will the slope of the cut face be? Assuming the cut face is stable, all you are faced with is some covering to prevent erosion. It all depends on the slope selected. I'd look into the "silo effect". I did a slope like this once and it took some estimate of "backfill height". As recall "not much".

RE: Retaining Wall Review

(OP)
The cut face is near vertical. Any thoughts on what the friction angle would be for the cement stabilised fill?

RE: Retaining Wall Review

The wall I refereed to was a new cut sloped back about 1 horizontal to about 6 or 8 vertical and stable in itself. The wall itself was large cut blocks of dolomite, no mortar. That was typical of the area (Dubuque, IA) but about 40 to 50 feet high. Somewhat unusual for the area. Drainage in back was required to avoid building up any water from above. That could be at the cut slope behind all that fill. The sloped cut of the soft weathered rock in back made for a much more stable situation than vertical. In your case, I'd be much concerned about any drainage from above getting behind a somewhat cohesive sand backfill and pushing whole thing over.
Thus lab tests for permeability as well as strength (friction angle and cohesion)could tell a lot as to what to do. Adding binder to the backfill may be a major mistake. For sure that wall ought to be porous, full height, as with precast blocks. I'd not use a cast concrete wall. Give thought to tied back construction also. A complete stability study, along with lab tests would be my thought. In connection with this, our recent area wide few days of 11 plus inches of rain might have taken down walls, but so far the news doesn't mention that.

RE: Retaining Wall Review

tclat,

This is a nice question that I don't have answer too. Let's keep it updated. I would like to know the binder effect on the backfill too.

RE: Retaining Wall Review

OG again. As I view this, it is an unusual kind of wall or earth cut protection, due to the lack of slope, width of backfill and a watershed up above. There maybe more things unknown to us here. Thus, I'd get back to the geotech with your question and inquire about any analyses done. Their experience with this treatment also would be good to know. I'd not try to second guess the geotech, but certainly ask for a complete explanation. You should be satisfied before doing the job.

RE: Retaining Wall Review

Hey, I'm still skeptical. Looking up Internet search for GeoMat comes up with info on its use for foundation wall drainage. I see nothing for using this as a covering for exposed earth near vertical surfaces "way up there". Documentation as to successful examples of use for protecting earth cuts from erosion, etc. definitely would be needed if I had anything to do about this job. Sit back and re-think what to do.

RE: Retaining Wall Review

(OP)
OG....the cut face is about 1H:10V. Why are you skeptical about the binder? Forgot to mention there is a cut off drain at the top of the wall.

RE: Retaining Wall Review

I say once more:
Documentation as to successful examples of use for protecting earth cuts from erosion, etc. definitely would be needed

Any protection from erosion helps, but none are perfect.

Oh, very important to check the geotech's insurance. They may need it.

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! Already a Member? Login


Resources

White Paper - How to Capitalize on HVAC/R Trends to Drive Business Growth
According to Steve Yurek, CEO of the Air Conditioning, Heating and Refrigeration Institute, the HVAC/R industry is facing change on all fronts. This includes challenging trends on contractors and distributors like new refrigerants, growing automation, complex sensors and monitoring, green initiatives and a technician shortage. We look at these trends and outline actionable insights on how it all can be turned into a competitive advantage and business opportunity. Download Now
eBook - Manufacturing the Cars of Tomorrow
In this ebook, we'll explore how additive manufacturing is going to transform the way cars are made. This includes commentary from thought leaders such as Ford's CTO, Ken Washington, Customer case studies of ways 3D printing is being used today, and a variety of part examples where 3D printing is already impacting how automobiles are made. Download Now
White Paper - Smart Manufacturing for Semiconductor
New technologies and approaches present great opportunities for semiconductor manufacturers to achieve high levels of innovation, yield and improvement. This white paper explores some of these cutting-edge technologies and how they can be applied effectively in the semiconductor industry. Read about how Smart Manufacturing is transforming the semiconductor industry. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close