×
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

Vertical component of active pressure in retaining walls
2

Vertical component of active pressure in retaining walls

Vertical component of active pressure in retaining walls

(OP)
This was discussed once on thread507-128311, but I'm not sure what to conclude about it.  Enercalc gives the option of using the vertical component of active pressure for retaining wall stability calculations.  Their structural engineer says there is some disagreement about using it in the literature.  My plan checker won't allow using it unless I can justify it.  Does anyone have an insight to whether to use the Enercalc option or not?

Thanks

RE: Vertical component of active pressure in retaining walls

If your using Rankines formula I would not but if your using Coulombs formula I would. What are the dimensions of your footing and wall height. Typically a gravity wall/no footing or a large footing with a small "heel" dimension justifies Coulombs formula. I don't have the Enercalc. Good Luck.

RE: Vertical component of active pressure in retaining walls

See the old standby:  Terzaghi and Peck (1967) - they have a few simplistic charts (4 cases) - which shows this I believe.

RE: Vertical component of active pressure in retaining walls

(OP)
Thanks BigH.  I have the 1967 edition of Terzaghi and Peck but can't find the charts you mention.  Do you have the page number? I've got to brush up on lateral earth pressure theory.

RE: Vertical component of active pressure in retaining walls

We totally ignore the vertical component of the active pressure, so we do not select that Enercal option.

RE: Vertical component of active pressure in retaining walls

I don't have the '67 version with me; the '95 version is in the office.  However, if you have NAVFAC's DM-7.2, go to pages 7.2-86 and 7.2-87. If you don't have the manual, go to VulcanHammer's web site - you can download it from there.
cheers

RE: Vertical component of active pressure in retaining walls

(OP)
Thanks BigH for the reference to VulcanHammer.  

I'm trying to picture the location of the active vertical component.  It seems to be acting on the stem, pushing it downwards.  Is that where it is?

RE: Vertical component of active pressure in retaining walls

petrosoft,

Yes, on the back face of the stem.

Jeff

RE: Vertical component of active pressure in retaining walls

(OP)
I've researched the issue, reading Coduto, Terzaghi and Peck and talked to Enercalc.  There is a vertical component of active pressure in the Coulomb theory.  Enercalc uses a coefficient of friction on the wall equal to 2/3 the internal soil friction.  That makes sense if the wall is concrete (rough) and the backfill is granular.  

I'm not sure when the Coulomb formulation is justified and when it isn't. Maybe that is the reason for the option in Enercalc.

Any thoughts welcome.  

RE: Vertical component of active pressure in retaining walls

Coulomb takes into account the friction between the soil and the wall; Rankine does not.  You can use Coulomb when it is appropriate to account for the wall friction and Rankine when it isn't.  

RE: Vertical component of active pressure in retaining walls

(OP)
I guess that when using a concrete or masonry wall and granular backfill, Coulomb is OK.


Thanks---Peter

RE: Vertical component of active pressure in retaining walls

When designing a cantilever wall (cantilever on soil side), the portion of soil above the cantilever is used as a resisting force.  The forces from the retained soil beyond the cantilever are assummed to react along a vertical section at the end of the cantilever.  Therefore, there is no wall friction and Rankine would be applicible.  

Coulomb could be used where there was no cantilever, or where the cantilever was on the exposed side of the wall.  In this case, the soil forces would be acting against the wall and friction would be applicible.

You do get a component of vertical force from Rankine where there is sloping backfill.  

RE: Vertical component of active pressure in retaining walls

(OP)
Hi moe333,

Cudoto's Foundation Design text (2001) page 797 states that the active component of vertical pressure is used to resist OTM in cantilevered retaining walls.  The development active pressure assumes a slight outward wall movement so the soil wedge falls slightly while clinging to wall with friction.  The only requirements are for outward movement of the wall and a rough wall surface.  I don't know if clay backfill would also develop long term friction force.

RE: Vertical component of active pressure in retaining walls

Clay soils tend to creep over time such that active pressures revert to at-rest pressures over time, even with wall movement.  Therefore, I would use at-rest pressure for clayey backfill.

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