Gravity retaining wall - Design reference 16

[LR11]

I was wondering of there's a recommended reference for the design of gravity retaining walls.
I'm looking into the design of a limestone block wall between 1.5m to 2m above ground level.

 

[SlideRuleEra]

Although the following are for proprietary retaining wall systems, their design manuals have pretty good coverage of the basics for gravity, and other types:

Allan Block Engineering Manual

Keystone Design Manual

http://www.SlideRuleEra.net

 

[Settingsun]

Hong Kong Geoguide 1 is also available online.

 

[Celt83]

this guide by the Colorado DOT has been the best resource I've found on rockery style walls: Link

My Personal Open Source Structural Applications:

https://github.com/buddyd16/Structural-Engineering

Open Source Structural GitHub Group:

https://github.com/open-struct-engineer

 

[dauwerda]

Here is a link to a design manual published by the National Concrete Masonry Association:

https://ncma.org/resource/srw-design-manual/

 

[LR11]

Thanks to both for responding.
In reading one of the references it mentions that "gravity" walls do not include those with mortar.
If you have a single leaf of blocks with mortar, what mode is considered, it wouldn't be bending would it? In the case with mortar, do you know of a reference. Maybe in reading the above it will make it clear.
Cheers.

PS. The notifications on this site don't really work.

 

[STrctPono]

I still use my Braja M Das (6th Edition) text book from undergraduate studies. That will talk about global stability checks for gravity retaining walls. I additionally follow my State DOT's requirement that checks stresses in the mortared stone and limits it to 100 psi compressive stress (under any loading condition), 0 psi tensile stress (under sustained loads only), and 10 psi tensile stress (with extreme event loads).

 

[LR11]

OK great, thanks for advising.
As a comment, a few months ago I do recall considering a situation with tension in mortar, with an allowable stress of 0.2MPa.
The reference: Technical Note 65, Bond Strength in Masonry Construction, CCAA.

 

[LR11]

Has anyone come across an example for an arrangement pf blockwork that increasingly tapers towards the base.
No footing.

 

[Settingsun]

That'd be similar to a gabion wall. I think you'll find more written about gabions than ungrouted rock walls.

 

[BigH]

Rule of thumb I've read and used for initial sizing is that the base to height ratio would be in the order of 0.7H.

See:

https://blockwalls.co.uk/gravity-retaining-walls/

 

[LR11]

OK thanks again.
I vaguely remember a free body diagram with a bunch of blocks and friction being induced as they rotated.
Unfortunate cannot find again.

 

[LR11]

With respect to this, I wanted to know if there are recommended design model/s.
With and without mortar. For plain blocks.
The closest I have seen is from Design Manual for Segmental Retaining Walls, from the National Concrete Masonry Association. But the multiple depth system is not addressed.
I have seen standard details and the rule of thumb guides, but wanted to get into the detail.

Or is it experimentally based? Or it it the tried and tested rules?

@steveh49, I couldn't find anything with respect to gabion walls to compare with.

 

[r13]

This should be just a simple stability problem, ΣFx = 0, and maintain M_R/M_OT > 1, at any given elevation.

 

[LR11]

Thanks for responding.
I can understand the shear stability.
With respect to overturning: Let's say you had multiple blocks without mortar. As they rotate individually, the sides would shear and press against each other. I don't know enough about retaining walls to know what limit state assumptions are made, the amount of rotation. So the blocks may have more capacity compared to the individual sum.
I wanted to see something and work through it until I was comfortable.
By the way, I'm looking at the "Multiple depth" case as can be seen in the image just before your post.

 

[r13]

ΣFx = 0, and maintain MR/MOT > 1, at any given elevation.

If the wall can satisfy the requirement, you should not have rotation problem, because it needs to overcome the friction to rotate. You can experiment with setting a few layers (1 to 3) of block with backfill, and see the result.

 

[LR11]

@retired13, I guess my query for rotation was in the sense of what would be allowed to engage friction between blocks, in the hypothetical design scenario.
For steelwork, plastic deformation is accepted and documented as a design model.
I don't have a good feel for a retaining wall with blocks though.
Just need to understand what's happening, given there is a masonry structure adjacent which doesn't like movement.

 

[r13]

You should be able to find answers from these document/articles.

Link
Link

https://files.engineering.com/getfi...d25e1b5b83&file=Segmental_Retaining_Walls.pdf

 

[LR11]

OK thank you but I have seen these and there is nothing specific to this application though.

 

[r13]

For steelwork, plastic deformation is accepted and documented as a design model.

I'm puzzled with the statement above. You are asking the rotation potential of a "rigid body", that does not posses plastic behavior. A rigid body subjected to a horizontal load will have two failure mode - sliding and rotation. Rotation will not occur, if it is allowed to slide. Rotation will occur under two conditions - sliding is prevented by shear friction (µW), and the resultant force falls outside of the pivot point. The whole point of the design of the SRW is thus to avoid the two failure mode with self weight of the blocks, and with the assistance of tiebacks (if necessary).

The bond is an important factor in retaining wall design. However the lack of bond strength is made up by limiting the height of wall, and making the wall more massive. For example, for a constant wall thickness, the concrete wall can be 10' tall, but be 8' for masonry, and 6' or less using dry blocks. However, by increasing the thickness for the latter two, the 10' height can also achieved for the masonry and block walls. Maybe I don't understand your question well, thus my answers are not to the point, but I sincerely hope you are not confusing yourself.