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View Full Version : Learned a lesson today....


PAPS
06-01-2002, 09:12 PM
Built a couple - Techo Creta walls... Now... There is very little/barely room to use Grid (irrigation/prop. line)... so we just went about building w/out. Was back-fillin with 3/4 but NOT compacting (don't ask me why we didnt..just wasn't think + in a rush i guess) So at one point in the wall... there was a lot of dirt excavated (about 5-6 ft. behind the wall, the rest of wall maybe 1 ft.) And sure enough in the area where there was alot of extra excavation... the wall caved forward.... We had it built to out final height (about 6.0 ft) and the weight of the loose gravel was just too much. So, before it caved... we noticed it bowed forward alot... so we began to take down that section to re-compact and put grid... and when i was walking behind the wall.... it fell forward... no one was hurt... but learned an important lesson on why compaction/grid is a must. Anyways... we had the whole wall re-built in 3 hrs... end of story...

Question? when using Creta... do u have to step the walls back over a certain height...??? we have a 6ft section... but it not 6 ft for too long... it gets smaller as it ascends up the drive.... maybe 6ft x 8 ft long.

paul
06-01-2002, 10:21 PM
I think you've found aout about banter:) Too bad it was the hard way. Critical walls need some form of retainage, whether grid or banter. Grid is a much easier and safer method but at times when you have no room for it or when you have problem sites banter can save your butt. If you would have had 1/4" of banter on the wall it would not have fallen forward.

Turfdude
06-02-2002, 06:16 PM
Bryan,

You know any wall over 4' should have an engineer's stamped seal on it. A goo friend of mine put in a large wall for a local diner. The wall is about 125' long 2 tiers ranging from a min of 4' to max of 9' - each tier. Anyhow, the top wall is not set back far enough from bottom wall IMHO, and bottom wall is setting on clay, and a lot of clay behind. They installed this wall w/out plans, and without geogrid. !.5 yrs later, kaboom - 40' collapse of lower wall into heavily traveled secondary road - on a Sunday. Crew sent 2 days rebuilding wall - with more stone backfill and geogrid.

They had plenty of pipe and all behind, but a soils engineer probably would have suggested some overkill methods to give some relief to the hydrostatic pressure.

Like you said ... lesson learned. Use the newly acquired knowledge and move on. Quality always surpases quantity in the end. "You can do the job right ... or you can do the job OVER"

Bob

paul
06-02-2002, 07:07 PM
I've been asked about banter, banter is installing walls with a lean to the inside of the wall. The wall is built looking like this \.
This provides for a stronger wall as long as the base course is buried deep enough. All walls over 4' should have a engineers stamp on them, but not too many engineers know about banter. It's easier for a engineer to use a companies information on the wall unit and add in grid. The hardest part is grading the first course to the correct back pitch. One more thing your base needs to be 6" to a foot deeper and you must reach 95% compaction on your back fill.

steveair
06-02-2002, 09:35 PM
Hello,

Max. height for creta/mini-creta built straight up is 30" unless grid is installed (you pretty much destroyed those specs if you built yours straight)

I know a lot guys prefer to build straight walls along drives becsause the set back of the blocks as they step up a incline don't follow the straight drive, but its wrong to do so if you are going to reach those kind of heights.

Max height for creta/mini-creta is 48" built with set back and no grid.

Anything over 48" needs grid/engineered with the set-back, while anything over 30" no set-back needs grid and/or engineered.

I believe I've mentioned this before, but will say it again. I really don't think such blocks as creta and mini creta should be used for anything over the specs. They really are more or less "decoravitive wall block" Techo can be built high, but requires much more support than many of the other systems out there.

Just look at the blocks. Versa-lok are 12 x 16 x 6 each. Some of the creta's are 9 x 6 x 3. Simple principles tell you that a wall built from 'little' pieces is going to be much less stable than a wall built from 'big pieces', and therefore is going to need extra help carrying a load.

At least it happend now instead of few months later when the job was finished.

My favorite thing now is all these new 'garden wall' blocks that have no means what so ever to connect to each other. they are just flat, square blocks that you stack on top of each other. I am seeing so many of these things go up around here to heights of 2, 3, even 4 ft! What are these people thinking? The spec sheet specifically says the a bonding adhesive must be used to connect the blocks for support, but I don't think I've seen one glued together yet. I'm just waiting to see the messes they make in a few years.



steve

LawnLad
06-03-2002, 10:23 AM
Question for you Paul....

When you speak of banter (I always thought it was batter... learn something new every day) - manufactured blocks have a set back designed into them, 3, 6, 12 degree set back. Maybe I'm confusing terms, but I thought that the setback/banter or rake of the wall was the same thing. Are you suggesting that the actual blocks of the wall are set on a pitch leaning back into the hill - and this is banter? Is this to say in this type of application that you don't set your blocks level?

paul
06-03-2002, 01:25 PM
Yes the actual block will be set off level. It's much harder to install this way, but you can increase the strength anywhere from 50% to 200%.

AGLA
06-03-2002, 06:25 PM
I could be wrong, but I would think that by pitching your wall back is going to weaken your wall toward global failure. That is when the material right behind the wall breaks from the slope rotating and pushing out the bottom of the wall. I thought batter helps against failure that topples the wall from the top.
I used Keystone a lot in a previous job. Although not the most attractive, it had a lot more mass than the solid stackables after you fill in the voids with gravel. We had nasty slippery silt & clay in very hilly terrain (the Palouse). Soil in fields would actually slump out occaissionally. Keystone worked very well up to 4' without geogrid in normal situations. ...It does not look as nice as most of these new products, though.
I like the look of Roman Pisa, but I sure see a lot of broken blocks in walls.

paul
06-03-2002, 07:03 PM
It can if not properly built. But when you need more holding power and you can increase the depth of the toe of the wall your strenght increases. Rotational forces on the wall can be controled. Latteral forces at the toe can be controled by reinforcing the toe with a concrete curb or better soils, plus proper back fill and compaction.