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Edgewater
01-28-2006, 07:20 PM
can someone clarify a few thngs for me.
I will not attempt a project before I am convinced that I know how to do it inside and out.

For a wall, i have 3 questions.

1) The drawings in the tech manual for the stone we use says to layers of geotextile to tie the wall back into the soil. What is the difference between goetex and grid. Also, how is it ancored to the block.

2) When backfilling the wall. Lets say it calls for 48 inch lengths of geotex as ties, is that whole area done with 3/4 clean and wrapped in geotex, or are the horizontal layers of geotex sandwiched with soil.

3) In the drawings, it show the 4 inch perf drain in the compacted 0-3/4 base below the footing, with the compacted base extending to the back of the backfill zone at a 2% slop. Do you guy put your drains in the 0-3/4 or in the 3/4 clean??

Just want to get this clear befor I build any wall. I have done several patios, but no walls.

cgland
01-29-2006, 11:10 AM
Edge - THe difference between geotex and geogrid is huge! Geogrid is material used to reinforce SRW's. Geotextile is a fabric used as a soil separator.
1) It is anchored to the block simply by laying it on the block and utilizing the block pins and next course to hold it in place. If your SRW has a lip system the weight of the next courses holds it in place.

2) The backfill material used in the grid zone would be up to the engineer. This depends on many factors i.e soil type, toe slope, slope behind the wall..etc. If you were just doing a 3-4' wall grid may not be a necessity depending on the block. In those situations (where I am approaching the manufacturers max height w/o grid I may throw a pull in depending on the slope and what I will be retaining.
Most cases you will be able to use topsoil for your backfill zone (behind your 1 foot of drainage stone. If this is the case and you have multiple pulls of grid you will have to wrap each segment with geotex. You don't want to wrap it totally, but just enough so that the soil will not leach into your clean stone. Then just place grid as usual.
3) We place our drain tile on the 3/4 mod. We slope the compacted stone to an adequate degree to achieve runoff. (If you use black corrugated, make sure you don't have any dead zones (dips that could trap water and impede flow)) Once we have our pitch, we place the drain tile on the mod stone and continue the backfill process w/ clean 3/4".

I hope this helps. I am not the best at explaing things while I am typing. I will try to find a diagram to explain #2

Chris

cgland
01-29-2006, 11:16 AM
Edge - go to Anchorwall.com

There, click on contractors and then cad drawings. There you will find a wealth on info and diagrams on all facets of SRW installation.

Chris

UNISCAPER
01-29-2006, 12:00 PM
If in fact that drawing tells you to use geo textile fabric to back tie your wall, call the design firm and question what they wrote. Ask for a revision on the specifications. If they refuse, fire the engineer and get someone who knows what the hell they are talking about.

Chris explained the differences very well. Even though homeonwers style manuals are the most basic and manipulated things ever written, I can't imagine a block maker writing that you use Geo Textile for back ties.

Edgewater
01-29-2006, 01:18 PM
I have posted a drawing of what the maual shows. I noticed that in the site Chris sent me to, the drain is right behind the footing and there is a pocket of 3/4 clean that brings water to the drain from the excavation line. Does it vary from wall type to wall type, or do you guys think that one particular drain placement is better?

Also, if you were to do 1 foot of backfill with stone, and the rest was soil, then I assume the drain must be right behind the wall. In that case, you have to wrap each pocket of drainage gravel with geo right?

I would like to see this done first hand, but most of the guys around here (In my area) are very paranoid and think that helping someone out is bad for themselves.

Thanks for the help.
Adam

cgland
01-29-2006, 11:36 PM
[QUOTE=Edgewater]I have posted a drawing of what the maual shows. I noticed that in the site Chris sent me to, the drain is right behind the footing and there is a pocket of 3/4 clean that brings water to the drain from the excavation line. Does it vary from wall type to wall type, or do you guys think that one particular drain placement is better?

It should always be against the back of the wall.

Also, if you were to do 1 foot of backfill with stone, and the rest was soil, then I assume the drain must be right behind the wall. In that case, you have to wrap each pocket of drainage gravel with geo right?

Exactly! But don't wrap it totally or your grid will not mesh with the stone and slide too easily.

I would like to see this done first hand, but most of the guys around here (In my area) are very paranoid and think that helping someone out is bad for themselves.

Some people are way too pretentious.

Chris

UNISCAPER
01-30-2006, 12:30 AM
Actually, depending on the site situations, you could have a pipe behind the wall, connected to daylight, and also a pipe at the cut line by the end of the grid. In this diagram, they show the cut line as being one straight line tapering up to the top of the grade. And, in reality, this is what we usually find when we arrive at sites where a grading contractors job was to make those earth cuts to build the wall along with his other site work.

What the ideal situation is, would be to step cut the back of the earth, so one cut would be at the back of the grid, the other about half way up would be another 2' deeper (farther away from the wall) than the bottom cut. This stops, or slows drastically, water from running down that cut line to the bottom of the footing.

The pipe you see drawn at the back of the cut in the drawing is used to extract water that would follow that cut down between the backfill in the reinforcement zone (footing) and the virgin soil where the footing cut stopped.

In the event of heavy rain, or a wet year, if water follwed that cut and found its way to the bottom of the grid, the soils could get wet and develope a condition the engineers call "plastcitiy". When that occurs, they turn to pudding, and that 95% compaction you worked so hard to get comes apart because there is no holding capacity. In the event water, (hydrostatic pressure) builds behind the wall, the grid can actually slide through the soil as the wall pushes away from the footing. The wall in this scenario can and will fail.

So, if the engineer calls for a pipe at that cut, you need make it perforated and place 3/4 gravel around it and daylight the pipe. You also need a pipe behind the wall. Connect them to a standardized drain pipe, and make sure water going through that pipe can be kept separate from the perforated pipe behind the wall. Don't use that black snake pipe. That stuff is not rigid and will eventually fail. I prefer SDR-35, rigid PVC plastic pipe.

There is one other thing I am curious about in this drawing. I see how they set a reversse pitch in the grade so water will drain towards the pipe.

What will not work is the place they show the bottom block. You show compacted base under the wall, but there is no embedment course, i.e. a course of wall in a trench that sits below grade. Not doing that will cause a global stability issue, because the wall toe will kick out. The standrd requirement for SRW walls is for every 8" of elevation, you need 1" of wall course buried (embeded) with a minimum of one full course below grade regardless of height.

I hope this helps!

Edgewater
01-30-2006, 02:52 AM
Not having and of the wall buried is my fault in the drawing.

What I wanted to know was weather the pipe should go on the same level as the footing, or below it. Also, as you said, there is a pitch away from the wall in the base agg., our local manufacturers spec it that way, and you guys (Chris) have show images of it pitched towards the wall with the drain right behing it.

I understand what you have said, and also that the homeowner type manuals are probably to generalized.

The only project that is on the bid horizon right now is a 3 foot tall wall about 50' long with flat lawn and no extra load at the top. I think that would be a good starter.


Thanks for all the clarifications

Adam

UNISCAPER
01-30-2006, 03:25 AM
It depends. In the ideal scenario, you would place the pipe on the leveling pad, with connections to drain the water that ran under the wall. Unless you can do that, you need to use the next best scenario. Place the pipe at the same elevation as the outside grade at the toe of the wall, then dump it out the wall face. If you place the pipe below grade with no place for the water to go, all it will do is sit there and cause trouble in the footing.

You should also have grid on the bottom course.

Edgewater
01-30-2006, 09:55 AM
Is there a particular manufacturer of Grid that is better than others?

I have never even seen it at any of the garden centers I buy from. But then again, we do weird things here like set pavers on stone dust.

Thanks again for all your help.

Adam

UNISCAPER
01-30-2006, 10:48 AM
Tony Risi lives somewhere near your area I beleive, and he was working through Unilock Montreal last I knew. He is actually the guy who invented modern day grids, he used to call his Risi-Grid. Try going through Unilock they should be able to set you up. If you are using Keystone, they have a great reputation with Strata-Grid. Then there is Tensar soil retention. That is a vinal product you have to cut with a saw.

For a 3' wall and no load, Strata 150 is probably good, is is a unilateral application, so you can install it both ways. Anything heavier than that you will have to cut because it is directional.

Check those two places out they should be able to help you.....

excalibur
01-30-2006, 11:01 AM
Actually, there are geotextiles that can be used for reinforcement. While it is not nearly as common of an application as using them for separation, they are out there, and they are a legitimate solution. A qualified engineer could explain their reasoning for such an application, and in my opinion, should not be fired because they will not change their specs. Now, keep in mind that not just any fabric can be used - it has to be a product designed as reinforcing fabric. For instance the thin grey stuff you use to separate say river rock when laid over clay would be virtually useless as Bill pointed out.

UNISCAPER
01-30-2006, 11:20 PM
Ya never know what you'll learn around here. I've never seen reinforcing fabric, let alone ever used it. Excaliber do you have a manufacturer in mind that makes this stuff? Like maybe Mirafied or someone ilike that? I am curious now to see what it is.

cgland
01-31-2006, 12:02 AM
I too have never heard of that. You would think that the "fabric" would need holes in it to achieve cohesion with the soil and give it a grip. I don't believe that a fabric can be used for this purpose unless there was something else involved in the installation.

chris

excalibur
01-31-2006, 01:33 AM
Bill,

Mirafi does indeed make some of it. Seems like you were talking with segmental retaining walls though, and you are correct, it does not really compete with geogrid because of cost and handling. Mirafi has a reinforce geotext line - you can see on their website. Chris - the weight and friction hold it in. Have you ever tried pulling out fabric that had a foot of rock on it? Nearly impossible. They use the reinforced fabric in wrapped walls and sometimes as reinforcement for gabion walls - Mirafi has case studies of each on their website. So, turns out Bill was right with regards to segmental wall stuff. When it comes to the landscape stuff, I should have checked first as I know Bill is the man when it comes to a lot of this stuff. But, when it comes to less pretty stuff (Usually for larger or hidden applications), reinforcing fabrics have their place. The strongest fabrics are very close in strength to the strongest of grids. Again, these are not the same stuff you use for separation.

Bill, thanks for starting the discussion - gave me a reason to go back and review some of this stuff that has been rolling around in my head for a couple of years.

Casey

casmi
04-12-2012, 12:25 AM
Can i use geogrid to tie back blocks but for the backfilling use light wt concrete & geogrid would be embedded in concrete