DIY retaining walls should not be more than 4 feet. 8 feet is not for the novice because of special engineering considerations to prevent the wall collapse. Anything you read on retaining walls should tell you your limit is 4 feet. For an 8 foot wall, you should consult a professional for advice on proper design, then you could still do the work yourself.

If I cut back into the hill side, is it plausible to make two walls that measure 4' per? Thus reducing the stress and providing a more decorative look at the same time with an area for plantings? I appreciate your response "gottagarden", and I hope you'll continue to give me any ideas you have.

The Dry Stone Conservancy is supposedly planning a workshop in Perryville, KY in the near future. You might want to look into it...

Here is a link that might be useful: Check this out...

Hey interesting topic.

I have seen a few retaining walls in my neighborhood that were laid on a very shallow angle. I would guess the rise to run was something like 3/1. So for an eight foot wall you would have like a 3 foot run. (I know my math doesn't work out) In that situation I doesn't seem that there is a lot pressure on the wall. I would guess however that if you are trying to retain fairly new material you stones might tend to sink in a bit.

Another thing I noticed is that they used a lot of fieldstone, so there were gaps, but they used small plants to fill in the holes. I looked really nice. If I get a chance I'll take a pic and post it.

Regards

Dave

treebeard, thanks for the heads up on the drystone workshop. I'll definitely look into that. I'm currently a student at UK in the Landscape Architecture program and have been commissioned for this job by a woman who thinks I should know it all already. Unfortunately I do not. actuary97, I would appreciate the images if you can get them, and my intent is to use plantings wherever I can as a sort of "green mortar". I don't have the space for a 3 foot run, however, so I'm looking into building 2 individual walls with a terrace for plantings between. If anyone has some more ideas, I would truly appreciate them. Thanks a lot for all of the responses!

treebeard, do you know WHICH Perryville, KY will be hosting the workshop? There are 3. Thanks.

If you've never constructed a stone retaining wall before, whether mortared or dry set, it doesn't matter..., an 8' tall dry set wall is not something you want to start off with. Even changing the design to 2 smaller offset walls carries with it the need for a little real engineering in order to understand the zones of influence of one wall's foundation & load upon the other, the load above the higher wall, the horizontal distance between the 2 walls, ground and surface (rain) water locally, the characteristics of the existing soils upon which the wall(s) may be founded, and last but not least, local or regional codes that may pertain to wall construction of given heights. Certainly, there are an inexperienced many who go forward with projects like this and many are successfully completed, but usually by chance and not design.

Old rules of thumb, by which many of us (older folks) still work, tell that the base of the wall should be founded upon and supported by a compacted layer of gravel or crushed stone at least 6" thick, all on top of native soils which have been previously compacted (with all organic soils removed). They tell us that the width of the wall's base should be about 40% of the height of the wall, and the base should be buried at least 12" below adjacent grade. They also tell us that the visible face of the wall should batter back at least 3 (horizontal) to 12 (vertical)...the back of the wall in that case being nearly vertical...and that the top of the wall (capstone) should be 12"-18" wide. Along the way, 'through-stones' should be installed at certain intervals both horizontally and vertically. (Through-stones being those whose ends can be seen at both the face and back of the wall, thereby 'tying' both faces together.) And,with regard to drainage of groundwater from behind the wall, they tell us to remember that the wall is dry set, without mortar, possessing a myriad of spaces that can carry water from front to back without the need for mechanical devices such as pipes (drain tile) or weeps. The important thing is placing free-draining material (like gravel or crushed stone) behind the wall 6"-12" thick to allow the water to migrate easily to the spaces in the wall.

Now, all of this should be viewed in the context of the type of stone being used. Rules of thumb are just that, nothing more, and shouldn't be considered engineering advice. Flat stones of nearly regular size and shape are fairly easy to work with. 'Found fieldstone', if anything like the native fieldstone found here in New England, is extremely irregular, tending more to the 'rounded' than the 'flat', and can be very difficult and time consuming to work with. It's not at all impossible, but best done by someone with experience. At the very least, almost each and every stone placement needs to be carefully thought out, reviewed, and reviewed again.

All of this being said, 'tis your project and your effort, so at the least, plan on it taking 4 times as long as you initially thought, making patience, care, and safety utmost in the course of events.

I appreciate your "suggestions", and they will all be taken to heart and considered very seriously when I start the project (That is, if I ever manage to remove myself from the fetal position I currently hold). Understanding that I may not be able to devote adequate time to this project, are there other methods for building the wall that will be more soundly constructed by myself, an amateur, and more time efficient? Other materials?

Sorry, I only know what the website tells me...it would be best to make contact with the Conservancy for more information.

I've never participated in one of the Conservancy's workshops, but I have participated in a few in which the stonemaster was a member of the Dry Walling Association in England, and have found them to be quite valuable...although mastering the techniques as required by the association to be eligible for the masters test is quite beyond my talents.

I would imagine the Conservancy's workshops to be similar in content and value.

Thanks so much for the information, treebeard. Your correspondence here has given me an itch to learn more about this topic and the art of dry walling. Living in Kentucky, in the Bluegrass region, they are crucial factors in our built landscape. There's a tradition and heritage in those walls that I believe won't be realized until I learn more about the difficulty of their construction. I appreciate the education you've provided me access to, and fully intend to take advantage of it. Every day is a new lesson. Thanks again.

Leaving native stone out of the equation, and hopefully the same with timber, one would be left with non-native, imported stone that can usually be found at larger nurseries or purveyors of landscape construction materials by the pallet, and are usually quite flat and easily stacked, or modular concrete block.

The former (the more shale-like stone of a flat nature) can be put together in a fashion similar to the 'rules of thumb' mentioned above, with less of the time consuming thought process associated with each stone. The mass of the wall would still, due to the laws of gravity, want to be in keeping with the 'rules of thumb', same with the base, batter, backfill, and drainage.

The latter, (modular block), has it's own set of requirements. Those vary slightly from block manufacturer to manufacturer, but are all basically the same. Block set 8' high will likely require the installation of a geogrid fabric at certain intervals within the wall extending into the grade behind the wall, as the wall progresses vertically, which serve as 'ties' from the wall into the earth behind the wall. Most block manufacturers offer blocks for both battered and perfectly vertical installation, but both will require the geogrid beyond a certain height, varying from brand to brand.

While the block is quite easy to stack, and the batter is pretty much figured out for the installer as it's built into each block section, the need to the geogrid tieback can slow things down.

And again, beyond the rules of thumb, there really is a need to examine the soils and the zones of influence in the design, prior to construction, to be sure that the walls will, in fact, stay where they're initially placed, even in the worst weather normally associated with a region.

Again, thanks for the great information. As for the soils, the region generally boasts heavy clay soils, bringing with them a high level of expansion or shrink/swell activity. This particular plat is home to a much nicer soil, higher in organic matter, and probably pushing more towards the silt/loam areas, so I don't fore see that as an issue. However, for cost effectiveness, she is now considering landscape timbers in conjunction with the stone.

My idea is to build the majority of the load bearing wall with railroad timbers, allowing terraces for planting areas and level places where I can construct small, non-loadbearing drystone walls. This way, I can place plantings in front of the ties in the form of evergreen shrubs to mask the unsightly appearance of the timbers. Once this is accomplished, I think I can create the appearance of a large stone wall by allowing the stone to show through in multiple areas, with no planting in front, but probably inside the "planter boxes" that will be created.

You seem to be the resident expert. Does this make sense to you? It seems that a retaining wall be easier constructed out of the larger timbers and they will create a reasonable base for the stone areas. Let me know what you think. Thanks a lot.

treyr

Although my years of being a fan of timber walls has long since past, there's really nothing wrong structurally with using timber as long as the timbers are properly connected together (using at least 60d spikes and/or rebar drilled and driven vertically through multiple timbers), and deadmen are installed at appropriate intervals to tie the wall back into the earth behind the wall. As for smaller stone walls above the timber elements, assuming that they are, indeed, small, and set back from the face of the timber wall some distance, then you're probably OK.

A couple of things to remember, though. Using real railroad ties means you'll get plenty dirty and covered with the 'treatment' that ties are known for. In the 'ol days, it used to be creosote. It may still be. Your client will also be exposed to same, and should be made aware of that. Using landscape timbers (6x6 min) as found at local lumber yards and big box outlets may be cleaner. But in the long run, wood is wood, and no matter how well it's treated, it will eventually succumb to the elements and Mother Nature...whereas stone goes on forever.

Of course, depending upon your age and that of your client, that may not be an issue, as in most cases, the longevity of the material is such that we may be long gone (or moved outta town) by the time things break down.