Rockery Wall with Geogrid reinforcement

[LordofDirt]

Hello,

I am new to the forum. I am looking for some general guidelines or a technical document on the design of tiered rockery walls with geogrid reinforcement. I have experience designing rockery (gravity) walls and experience designing MSE walls, but I am not sure exactly how to approach this problem.

My first thought was to use the miraslope software for design of a reinforced slope with a batter of approximately 10 degrees and then the rockery wall would just act as a facing.

Any help is appreciated.

Thank you

 

[TigerGuy]

I've never seen a rockery wall with geogrid reinforcement. Typically, rockery walls are used for cut embankments, and geogrid reinforced walls are used for built up areas.

 

[LOTE]

I have designed several of these. I will use a combination of Vespa and MSEW+/Ressa. There is not a great resource for this, but you will find some helpful info in FHWA-CFL/TD-06-006.

Some things that I think are important:
1. Limit the connection strength to something lower than you would with an SRW block.
2. Confirm the rock sizes. Generally this limits your minimum spacing and will control the required strength for your geogrid. For instance, the maximum vertically spacing of geogrid for a coherent mass is 30", so vertical height of the rocks will need to be limited to less than this.
3. A lot of times contractors will use more of a rip-rap in the drainage stone section versus a #57 stone to keep the rocks for spilling out. This will increase the installation damage on the geogrid.

I am happy to answer any additional questions you have.

 

[LordofDirt]

Lote,

Thanks for your response, very helpful. In your designs for these walls, is the geogrid actually connected/sandwiched between the boulders? or is the geogrid wrapped and independent of the rockery wall?

Thank you

 

[Jrit]

It is in the one's we design (grid installed between boulders, similar to a block wall). Similar methodology to LOTE. I also agree stepping up the grid strength a bit due to damage.

 

[LordofDirt]

May I ask how the geogrid is placed between the boulders? With the rockery walls I see, the courses of rock rarely align in linear rows, this would mean the geogrid would have to follow the uneven alignment of boulders as well. Do you have any photos or details you could share?

Thank you

 

[LOTE]

Yes, in my designs the geogrid is sandwiched between the boulders, like an SRW. I put a maximum spacing between each layer of geogrid to allow for some tolerance for different rock sizes.

Here are a few pictures. I generally see more rectangular shaped boulders for this application, like from outcropping rocks. The contractor can arrange the rocks by size to get fairly uniform lifts. Round boulders would not be a good application for this.

 

[geotechguy1]

I done one of these, similar approach to LOTE - Vespa / MSEW. The hard part is that the geogrids are friction fit and there isn't really alot (any?) data you can use for pullout. Another approach would be to design it as a wrapped face and then basically just have the rocks as a facing

 

[LordofDirt]

All,

Thanks for your help.

LOTE, your pictures are very helpful. In my area, the boulders we use are large and more rounded and achieving relatively level courses of rock is much more difficult.

GeotechGuy1, My approach will be similar to yours. with wrapped geogrid behind a veneer wall. Do you use a reduction factor for the pullout?

Thanks

 

[LOTE]

With the wrapped approach, as long as the wrap is sufficiently long (permanent wire face wall typically use 4'-5'), then no reduction in pullout is needed.

 

[DarronC]

LOTE;
You must not have any seismic forces in your area.
We typically use 75% of the wall height as grid embedment. Rock fitting is critical. I usually request one extra long rock for every 7 rocks, which will pin the two below, the two above and the two on either side.

We put a swale to redirect the water coming down the slope above the wall.

 

[DarronC]

LoD;
You may find it useful to split your boulders, along their long axis, into quarters. This will create easily stackable triangular sections. You can use a 3/4" Hilti rock drill and feathers and wedges. It goes very fast.