Riprap for retaining wall?

[pago cruiser]

Finally - after about 10 years... getting my 40x30 started. Sticks and stucco, nothing fancy. But part of my driveway has a short (50') length of 16% slope, and the garage approach has a cross-slope I am trying to minimize.

Need about 200 LF of 2-4+ foot retaining wall, in basically a long arc. This will contain about 500 yards of fill, and bring the garage approach to about a 5% slope; which I think I can live with. I would also be adding to one side of the driveway in order to level it as well. So this will be vehicular load bearing.

Have looked at massive overfill (basically fill dirt sloughed out for 10-15 feet from the finished edge) poured concrete retaining wall (really, really pricey), concrete footings and blocks (really pricey), segmented blocks (pricey), gabions pricey, but I do not know why? metal baskets and river rock), shotcrete (lots of big equipment and skilled labor = kinda pricey), and today a local Contractor suggested to just keep it simple and cost efficient - Riprap.

Property is outside Tucson, 4000' foot elevation, and I am on a hilltop - so no drainage or groundwater issues. While southern AZ gets their usual monsoons (as they call them, with their about 6" total during the summer - which is actually rather farcical if you have ever lived in a rain forest that sees 200" a year... but I digress), it is generally dry. Hence, the desert moniker. So I am not too concerned with water issues undermining or washing away the rocks.

Has anybody used this for this application? Pics? Tips? Issues?

Thanks.

Kinda like this; but a little taller, lots longer, with 5-7" rocks:

 

[ccogg]

It’s possible to make a good wall with rocks, but 5-7in is really small. It all depends on the angle of the wall.


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[wayout]

I'd go with the contractors advice but also include geogrid in the project. Even though you don't expect water to settle the riprap, gravity will.
Gravel travels no matter what size and finding the angle of repose for the material being considered will help determine if your plans will work.
Sharp, chunky stone along with geogrid should do it.

 

[SundayFunday]

Kinda like this; but a little taller, lots longer, with 5-7" rocks:

You might want to clarify what kind of wall your contractor is calling riprap. In my mind, your picture is a "Boulder retaining wall" and is not cheap.

Riprap as I'm familiar with is smaller rock dumped over sloping ground to prevent erosion .... very often used on shorelines.

Still works, but be sure you getting what you envision.

 

[Mainiac Mat]

Dropping a couple hundred bucks to have a civil engineer advise you might be a worth the effort. The little lizards will love you if you go with the riprap, but 4+ feet is kind of getting up there in my mind.

 

[firebirdparts]

My dad has a mile long driveway that he built over very steep terrain and that he's maintained for 60 years now. We get 10 times your rain plus snow and freezing. It seems to me that you don't actually need a whole of effort to hold that road still in Arizona. If you are going to have a concrete driveway, then your main concern is just to avoid any movement that would lead to damaging the driveway. But you may not be planning that, I don't know. If the road is not paved, honestly, you wouldn't need any of these things. Around here earth will hold a 100% slope if you just stay off it, but of course that's clay.

Without rain, material ought to stay where you put it. The big detriment to rip rap, as I see it, is lawn maintenance around it. If that doesn't bother you, I think it's gracious overkill in the desert. I don't know if you water grass or mow, but that would be a consideration. If it's just scrubby desert then you would be fine with the appearance of it, I think. I have always loved the appearance of limestone.

 

[nadogail]

are you talking about mesh bags of cement, sand and gravel stacked dry like I have seen along riverbanks?

In my opinion it works fine, if you have enough time and money. The labor in filling, carrying, and stacking those bags would scare me away.

I am sure it works fine because I have seen it used to protect bridges; but the expense of all the labor to mix, fill, carry, and stack those heavy bags relegates it to major budget jobs.

 

[tarmy]

Yep...

Needed a trailer storage area...and a place to wash boats. Neighbor was cool with it as I wanted in near the property line too.

It is best to use angular rock. I only had what was around...volcanic round type...but lots of it!.

I have a backhoe on my tractor with a hydraulic thumb which made it possible to stack the rock. The first course must be bedded in a key way to prevent the wall from blowing out. The layback of the wall is important as well to keep it from toppling over.

 

[csp]

I have built a couple of retaining walls using rip rap. They really don't do much "retaining" as the slope behind them was stable and about a 3:1. I just wanted a sharp cutoff between my lawn and the natural landscape.

It's a lot of work and a lot of time to determine which rock to place where. The second wall, which isn't pictured but is where the falling over railroad ties are, took less time as I got the hang of being able to visualize placement vs trial and error.

The top of this wall isn't a constant height as I wanted it to follow the existing elevation. It hasn't moved a bit that I can see in the 12 years it has been in place.

I had 20 tons delivered and probably used all but two of them.

 

[csp]

Duplicate post in error

 

[ccogg]

Beautiful wall!


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[sweetk30]

if you dont need super fancy call local concrete places that do bulk delivery for big jobs . they make and sell BIG blocks in both smooth and textured face finish for jobs like this . they take a big piece of equipment to set them but they dont move much at all after . i see lots of people use them around here and there still were they were set . even the state / county use them for water control in creeks and small rivers here to funnel the water in the tubes under roads so the water dont wash away the bank edges . you can gain usable space also since they can be stacked straight up and not needed to tapper out as much as smaller stuff or rip rap rocks .

here is a site with them in all styles and uses . https://inter-block.com/

 

[theoldwizard1]

The riprap as I'm familiar with is smaller rock dumped over sloping ground to prevent erosion .... very often used on shorelines.

Just the opposite of what I have heard ! Usually very LARGE rock as they have to prevent the waves from eroding the soil behind.

 

[theoldwizard1]

Need about 200 LF of 2-4+ foot retaining wall ...
I would also be adding to one side of the driveway in order to level it as well. So this will be vehicular load bearing. ...
taller, lots longer, with 5-7" rocks

Normally, Tucson would be a good place for a loose rock wall ! Water and freeze/thaw cycles is what causes them to fail. However, the additional weight of the concrete driveway and vehicle traffic are not a good idea. Even if the wall doesn't fail completely, I think the fill will settle and crack the driveway.

Most retaining walls fail for two reasons: 1) inadequate footing and 2) inadequate drainage.

 

[rustyjames]

Gabion walls could be another option.

 

[Copymutt]

Caliche won’t settle further than it already has, unless you jackhammer it.

 

[theoldwizard1]

Gabion walls could be another option.

It would still need some serious deadman anchors to prevent them from moving.

 

[AP514]

Caliche won’t settle further than it already has, unless you jackhammer it.

You lived in Tucson also

To the OP are you Far East or North in the foothills ?

 

[four.cycle]

"The riprap as I'm familiar with is..."

Obviously from the responses the definition of "rip-rap" varies by geographic location.
In Western Washington, Oregon, and Northern California, THIS is "rip-rap" (aka "bank armoring"):



^ the rocks in the foreground at right vary from about 18" - 36" in length.

 

[pago cruiser]

Thanks all for the comments and ideas. Some great wall pics as well.
I hope to visit some sites this weekend to see what the Contractor is referring to.

To answer some of the comments:
The "5-7" size is what I remember seeing somewhere around here in a similar application; but it was for a 20' length driveway - not a 200' long curved mass that varies in elevation by 10'.

I did look at gabions - but the Shotcrete guy indicated gabions are about 2x his price for the height (about 4') I am looking at. As I am trying really hard to avoid the dam site work costing more than the garage... I think gabions are out. Although they would seem (to me) the cheapest and easiest systems with 1) a graded flat area, 2) 20 baskets (at 10'L x 3' x 3'), and 3) around 3.3 yards of rock in each. Seems a perfect job for day laborers - and not necessarily requiring Union Mason Contractor to set each stone. As I think about it though, I need 4 feet; but I have seen gabion cages in excess of 6', so that would not be a deal breaker.

I discussed the riprap with a Civil acquaintance. The Contractor was suggesting a 1:1 riprap slope. The Civil suggested a 2:1; but with the caveat that he does not use riprap in this manner. He (the Civil) did suggest on "stepping" the riprap - as opposed to dumping rocks and just following the contours.

The Contractor did mention using a toe-in - not sure how far he is thinking - as well as some geogrid.

Speaking of caliche - that is pretty much what my entire property is, with a few areas with 3-6" sand topsoil - mostly around native vegetation. I've copied this from a site with a good description:

"One of the most obstinate aspects of dirt in the Sonoran Desert is the concrete-like caliche (pronounced kuh-LEE-chee). The name comes from the Latin root for calcium, and it is referred to as the calcic horizon by soil scientists. Calcium carbonate cements particles together, forming a rock-hard layer among sandier deposits of mineral soil. These layers of hardpan can be as much as 6 feet thick in Southern Arizona."

For power, I am going to have to trench about 120LF at 36" deep. This is going to ****; but is a problem for later...

I like the idea of those giant blocks; there is a pre-cast place (Jensen) in Phoenix who apparently make them. Could not find any costs however. And they would definitely require stepping the wall. One problem I see is that my max height is about 48" - and the Jensen Big Blocks are only 18"H.

I've attached an excerpt of my site DWG to show the scale of this convoluted cluster thing - at about 200LF it warrants getting it right the first time... It is still showing a gabion wall in an arc from top left to lower right.

I am amazed that everything I need to get done seems so...complicated.

 

[Roadster J]

Riprap is a surface cover for erosion protection. It is not an earth retaining structure. Of course you could build a wall with the riprap stones, but then you would have a wall, not riprap.

If the underlying soil is stable at the angle your proposing, then riprap could be used as the surface cover to protect the underlying soil from water and wind erosion.

If the soil is not stable at the proposed angle, then the structure has to retain the material behind it and you are talking about wall. The wall will have to resist the active pressure of the soil as the soil will be pushing against it.

If you need a wall, I think the style/type you are looking for would be a “rockery wall”. Stone size would be larger starting in a 12”-18” range.

I have a booklet of some general rockery guidelines on the network at work. It’s old but it might be good for background information. I will look for it when I am in the office.



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[pago cruiser]

That's kinda what I had always thought; yet the Contractor seemed to be pushing this, and my Civil acquaintance guy did not push back - one bit.

A "Rockery wall" sounds a bit more suitable; kinda like the big block things. But I think you are right, in that as long as the angle of repose is stabile, any of these things are just a... pretty border.

Would appreciate the Rockery Wall info.

 

[Mainiac Mat]

Might help to define what is meant by rip rap.

Around here (north east) it's refers to rocks that are the size of your fist to the size of a pint of milk. It is often put in drainage ditches along sloped sections of road. The idea is to slow down the flow of the run off to minimize erosion.