×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Are you an
Engineering professional?
Join Eng-Tips Forums!
• Talk With Other Members
• Be Notified Of Responses
• Keyword Search
Favorite Forums
• Automated Signatures
• Best Of All, It's Free!

*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.

# Cantilever Retaining Wall - Soil Pressure

## Cantilever Retaining Wall - Soil Pressure

(OP)

I have a question regarding the eccentricity of retaining wall footings, in regards to calculating footing bearing pressures.
â€¨Below is a quick overview of my procedure.
-neglect passive resistance
-neglect overburden on toe

B = base width of footing
Mo = overturning moment
Mr = resisting moment
Ps = weight of soil + weight of concrete

I calculate the eccentricity:
e = (Mr - Mo) / Ps

I check if the eccentricity is in the middle third:
e > B/6 (if it is not in the middle third)

Lets say it is not in the middle third, for sake of discussion. I know that this is not always a deal-breaker, but lets say I want to get e < B/6. Are there any dimensional changes that I can make to the structure (excluding decreasing the stem height) that will decrease the eccentricity?

My initial guess was to increase B.
-if I increase the toe width, then Mr increases due to the larger moment arms
-if I increase the heel width, then Mr increases due to the weight of the additional soil on the heel.

In both of the above cases Mr greatly increases, thus increasing the eccentricity.

Am I looking at this incorrectly? Or is there no easy way to decrease the eccentricity on the retaining wall footing?

### RE: Cantilever Retaining Wall - Soil Pressure

I think that your equation is correct for level backfill. Besides increasing B, you can use granular backfill which has larger angle of friction and unit weights.

### RE: Cantilever Retaining Wall - Soil Pressure

For the simple case of level backfill, increasing the footing heel below the backfill increases your factor of safety, lowers your max bearing pressure. Every time.
Sloped backfill is more complicated, where increasing the footing heel dimension increases both driving and resisting moments (not equally, though).
There are many retaining wall example problems in concrete text books, and the CRSI retaining wall (chapter 14) discussion and example is helpful and commonly referenced.

### RE: Cantilever Retaining Wall - Soil Pressure

Are you using factored design loads? If so, I believe there is a different limiting eccentricity.

### RE: Cantilever Retaining Wall - Soil Pressure

(OP)
Thanks for the responses. I will look at the references.

If I continue have problems I will scan a copy of the calls.

Thanks

#### 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.

#### Resources

eBook - The Future of Product Development is Here
Looking to make the design and manufacturing of your products more agile? For engineering and manufacturing organizations, the need for digital transformation of product development processes just became more urgent than ever so we wanted to share an eBook that will help you build a practical roadmap for your journey. 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:

• Talk To Other Members
• Notification Of Responses To Questions
• Favorite Forums One Click Access
• Keyword Search Of All Posts, And More...

Register now while it's still free!