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Gravity retaining wall - Design reference
16

Gravity retaining wall - Design reference

Gravity retaining wall - Design reference

(OP)
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.

RE: Gravity retaining wall - Design reference

2
Hong Kong Geoguide 1 is also available online.

RE: Gravity retaining wall - Design reference

(OP)
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.

RE: Gravity retaining wall - Design reference

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).

RE: Gravity retaining wall - Design reference

(OP)
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.

RE: Gravity retaining wall - Design reference

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

RE: Gravity retaining wall - Design reference

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

RE: Gravity retaining wall - Design reference

(OP)
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.

RE: Gravity retaining wall - Design reference

(OP)
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.

RE: Gravity retaining wall - Design reference

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

RE: Gravity retaining wall - Design reference

(OP)
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.

RE: Gravity retaining wall - Design reference

Quote:

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.

RE: Gravity retaining wall - Design reference

(OP)
@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.

RE: Gravity retaining wall - Design reference

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

RE: Gravity retaining wall - Design reference

Quote:

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.

RE: Gravity retaining wall - Design reference

(OP)
The above is for a single block only. I can understand that.
Take the hypothetical case for three blocks.
The overturning restraint offered by three individual blocks is 3.Wi.T/2, where Wi is the individual weight and T is the thickness.
For a hypothetical single block, 3 times the width, the restraint is 3.Wi.3T/2 ... 3 times as much.
What I'm guessing is that the actual restraint is somewhere in between, because of the friction developed.

Is the normal practice to take each block as acting individually then?

With respect to the tiebacks, I don't believe they are actually used locally, I could be wrong though. Not sure if I mentioned, these are reconstituted limestone blocks, 0.35m x 0.35m in section, 1m long, plain faces (without keys/protrusions), soil is sand-clay profile typically.

RE: Gravity retaining wall - Design reference

Redi-Rock has some useful design tools. Their older manuals are more designer-friendly. A lot concrete suppliers in the NE USA stock forms for some type of Large Block Retaining Wall.

RE: Gravity retaining wall - Design reference

(OP)
This is what is done locally.
The hatched blocks are in the transverse direction and are perhaps an interlocking mechanism.

RE: Gravity retaining wall - Design reference

The wall is designed to match the backfill pressure, minimum on top, maximum at the bottom, with the transverse blocks, it forms a grid system, which is quite stable. A very pleasant and stable wall, just by eyeball it.

RE: Gravity retaining wall - Design reference

(OP)
OK thanks for your comments.

RE: Gravity retaining wall - Design reference

For those walls that are several blocks wide in cross-section and which have no tension capacity between blocks, I've only ever seen checks of: friction at the various levels; and middle-third resultant location for full wall height required. But I've never been quite convinced this is sufficient for internal stability, ie no further checks required. Especially for irregular stone where the contact points between various stones may not be ideal from a theoretical perspective.

RE: Gravity retaining wall - Design reference

(OP)
Thanks for commenting.
If block/block or block/soil friction coefficient was below 0.5, the shear stability would govern, regardless of assumptions. The friction values for block/block are above 0.5 from what I looked into last week, for limestone.
Not that I can't do the statics but I wanted to know what the tried and proven method was, with and without mortar. I don't have any knowledge either of experimental or factual evidence ... for that reason I wanted to see a How-To guide.

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