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Mike33
07-16-2007, 10:09 PM
here is some pics of a large srw that failed in my area. This wall is around our new hospital under construction. The height is some places looks around 30-40' and must be arond 1/3 mile long. 2 months ago i drove by and took a slight look and thought that wall has a heck out a bow in it, na couldnt be. The next week it blew out . An out of town contractor must be in deep crap. Look at the drainage stone, 1' wide hell i have more in a 3' wall than they have here. They are actually re-building it back up the same domb way i think that is in pic 1 or 2. The backfill soil was all clay. Check out pic 5 does it look like it is leaning also?
Mike

crab
07-16-2007, 10:45 PM
ok there is a time and place for wall bricks .this my not be the one.

tthomass
07-16-2007, 10:54 PM
That hurts......I bet they were low bid though!

ChampionLS
07-16-2007, 10:59 PM
A job of that size, I'm sure they know why it failed. Looks like Keystone block. It has no locking back lip,only a 5/16" fiberglass pin to hold it. Each block usually takes two pins. Not good enough for my liking.

crab
07-16-2007, 11:03 PM
:laugh: dude keystone block whatever,look how the slope is cut ,may i suggest rock ,maybe large rock????????

ChampionLS
07-16-2007, 11:07 PM
I saw a Allan Block wall job today that almost made me crash my truck. I didn't have my trusty camera, but I WILL take some pictures tomorrow. Wait until you see how some moron stacked these blocks up! OMG...it doesn't get any worse than this.

Mike33
07-17-2007, 07:11 AM
What do you think of the last pic? Dont it look like the top is leaning?
mike

turfquip
07-17-2007, 07:56 AM
Yes, it appears to be leaning.

Why no Geogrid? It will fail again IMO, I just hope no one is injured or worse when it does.

The weight of the blocks stacked 30 feet high and all the gravel behind it will push it forward. There's nothing to hold it back.

D Felix
07-17-2007, 01:32 PM
Those are NOT Keystone. I'm not 100% sure what they are, but I think they are Rockwoods.

I'm not very familiar with Rockwood, so I do not remember if they use pins or not. FWIW, I would much rather have pins (Keystone or Versa-lok) than a back lip like Anchor. I've used all three, and I am certain the Keystones and VL's are NOT going anywhere. Can not say the same for Anchor...

There is geogrid there- don't you see it hanging down from the backfill soil? That's part of the reason pinned blocks are inherently better than lipped- you have positive contact with the grid....

GroundScapesIncorporated
07-17-2007, 03:43 PM
Those are NOT Keystone. I'm not 100% sure what they are, but I think they are Rockwoods.

I'm not very familiar with Rockwood, so I do not remember if they use pins or not. FWIW, I would much rather have pins (Keystone or Versa-lok) than a back lip like Anchor. I've used all three, and I am certain the Keystones and VL's are NOT going anywhere. Can not say the same for Anchor...

There is geogrid there- don't you see it hanging down from the backfill soil? That's part of the reason pinned blocks are inherently better than lipped- you have positive contact with the grid....

I think you are right.
Looks like Rockwood to me as well.
I do not believe Rockwood has pins.

I have seen many many pictures of failed walls and never seen one of Versa-lok or other pinning style walls that had failed.

D Felix
07-17-2007, 04:10 PM
Sheshovel posted some pics of a Keystone wall that failed. However it simply blew out- the faces of the block came off, leaving the tails. That wall, though, had a LOT of other issues un-related to the geo-grid and pinning.

I am somewhat sure that had that Rockwood wall been engineered and installed correctly (as long as the hieght and other specs were within manufacturer specs), it would not have failed. I don't know of any walls that failed due to poor manufacturing....

mrusk
07-17-2007, 06:43 PM
Mike, I have never had a wall plan done by a engineer that called for more then 1 foot of 3/4 clean stone.

GreenMonster
07-17-2007, 10:06 PM
There is geogrid there- don't you see it hanging down from the backfill soil? That's part of the reason pinned blocks are inherently better than lipped- you have positive contact with the grid....

Ya know, I've brought this up here before, and no one has touched it, but, if the function of geo-grid is to stabilize the soil, why does the contact with the block via lip or pin even matter?

From what we're being told about geo-grid in NCMA classes, or any SRW manufacturer sponsored course, the grid should be able to go up against the back of the block -- that is, not even contact the block -- and do the job of soil stabilization as it is being sold to us. thoughts???

Mike33
07-17-2007, 10:17 PM
Mike, I have never had a wall plan done by a engineer that called for more then 1 foot of 3/4 clean stone.
I agree you are more than correct. I do it as a piece of mind. My feeling is the more drainage stone used the more pressure is taken off of that wall. Of course with some of my new competion i bid against it is tough to supply all the stone i have been doing and be in the price game.
Mike

Mike33
07-17-2007, 10:23 PM
Ya know, I've brought this up here before, and no one has touched it, but, if the function of geo-grid is to stabilize the soil, why does the contact with the block via lip or pin even matter?

From what we're being told about geo-grid in NCMA classes, or any SRW manufacturer sponsored course, the grid should be able to go up against the back of the block -- that is, not even contact the block -- and do the job of soil stabilization as it is being sold to us. thoughts???
Good point, i use open core and i would think when i place the grid under and fill the block with clean stone all that weight would hold the grid as good as a pin. However i watched this wall being built it was actually backfilled with all clay and if it rained the day before it was wet fill, they didnt care. It came from the other side where hosp. was being excavted and moved in for the wall. The excavter cont. was on a dead line and was giving away fill so guess who didnt have to buy any fill?
Mike

Henry
07-17-2007, 10:52 PM
If you look closely at the rockwood blocks they have a raised square on top that is used for connection.

Mike, do you remember how far back they excavated for that wall?

senatorcongressman
07-18-2007, 08:34 AM
I'm no soil engineer, but I would imagine there is some spec for how much expansive soil needs to be removed from behind a wall, as a function of its height. (I'm thinking angle of repose here) Preaching to the choir, but expansive soil (clay) is not a suitable backfill for a wall. No amount of Geogrid is going to keep that clay from expanding and pushing against the wall. That's why the top (what's left of it) is leaning forward.

There is a bound-to-fail wall of similar height outside Lowes near my house that gives me the creeps every time I drive along side it. I'll snap a pic next time I'm there.

PatriotLandscape
07-18-2007, 06:06 PM
40' tall and no grid gotta love the low bidder.

Mike33
07-18-2007, 06:55 PM
I dont remember excavation that well, it is close to me but off of my path. I do know the block didnt have no batter it was speced to go straight up.
Mike

Mike33
07-18-2007, 07:00 PM
40' tall and no grid gotta love the low bidder.

Look a little closer Patriot there is grid, they have it pinned back to the bank. I dont know on how many courses they did or how far back. The funny thing is look close at the pics, it fell out to the ground level and they are building it back the same way. Wouldn't you of thought with a zero batter you would probably darn near have to grid every course? I have never worked with a batter like that to know the grid specs.
Mike

turfquip
07-18-2007, 09:58 PM
There is geogrid there- don't you see it hanging down from the backfill soil? That's part of the reason pinned blocks are inherently better than lipped- you have positive contact with the grid....

OK my bad... I first thought that had been used as a soil separation fabric and not in a soil stabilization (as in engineered) role.

ChampionLS
07-18-2007, 10:19 PM
Everyone hold your horses. Theres a lot of different thoughts going on here. Geo-grid serves two purposes. 1) it does stabilize the soil, but only by acting as a tie back, as it locks the wall with the soil mass. 2) Placement of Geo-grid is critical, along with it's length. The retained soil mass needs to be brought up to grade with the appropriate course of block, and compacted.

Adding more than one foot of drainage aggregate will put stress on the wall, as the weight of the stone and it's mass need to also be retained. There is no cohesiveness with loose stone.

Clay should never ever be used as back fill in any wall project. The back filling was done by bulldozer or whatever probably helped heave the wall forward. They should have trucked in suitable fill, such as bank run gravel, which is free draining and compatible. This wall looks pretty vertical. I bet the batter is less than 3 degrees. For that height, 12 degrees would be optimal.

Mike33
07-18-2007, 10:27 PM
Everyone hold your horses. Theres a lot of different thoughts going on here. Geo-grid serves two purposes. 1) it does stabilize the soil, but only by acting as a tie back, as it locks the wall with the soil mass. 2) Placement of Geo-grid is critical, along with it's length. The retained soil mass needs to be brought up to grade with the appropriate course of block, and compacted.

Adding more than one foot of drainage aggregate will put stress on the wall, as the weight of the stone and it's mass need to also be retained. There is no cohesiveness with loose stone.

Clay should never ever be used as back fill in any wall project. The back filling was done by bulldozer or whatever probably helped heave the wall forward. They should have trucked in suitable fill, such as bank run gravel, which is free draining and compatible. This wall looks pretty vertical. I bet the batter is less than 3 degrees. For that height, 12 degrees would be optimal.
Read my earlier post on batter of this wall.
Mike

ChampionLS
07-18-2007, 10:32 PM
I did.... thats crazy!!! Anything that's built straight up, and then back filled will no longer be straight up. For the same reason bridges are arched. The shortest distance between two points is a straight line. If a bridge was straight, it can easily bow down, sag and eventually fail. When it's arched up, it's longer than a straight line and can't compress. By design it's fail proof. A wall that has zero degree batter rely's 100 % on the weight of the block, and lots of geo-grid to hold it there. I hope nobody got killed when it fell over.

Mike33
07-18-2007, 10:48 PM
I did.... thats crazy!!! Anything that's built straight up, and then back filled will no longer be straight up. For the same reason bridges are arched. The shortest distance between two points is a straight line. If a bridge was straight, it can easily bow down, sag and eventually fail. When it's arched up, it's longer than a straight line and can't compress. By design it's fail proof. A wall that has zero degree batter rely's 100 % on the weight of the block, and lots of geo-grid to hold it there. I hope nobody got killed when it fell over.
What is really bad, very embarassing for my area is that this is our new hospital. This wall is probably 1/3 mile long is cars going to be parked up there? I e-mailed by sales rep whom is out of the area she told me they ( ab ) bidded the block and the specs was for a vertical wall. Ab has a 3 degree and which is still damn near straight up and they bailed out. She even said a vertical wall has 1 way to go, fall over. Also every one here gets on the enginered kick when i speak of bulding 6' walls. How about the stupid sob that enginered this one? I sure as hell would not go with his plan. I'll try to get some more pics this week end if i can get closer, but hell i really dont feel like getting close to any parts of this one. Check out the last pic i swear that part is getting ready to go.
Mike

orionkf
07-19-2007, 01:16 AM
1) it does stabilize the soil, but only by acting as a tie back, as it locks the wall with the soil mass. 2) Placement of Geo-grid is critical, along with it's length.

1) Disagree. I thought it stabilized the soil by breaking the natural shear plane, enabling the reinforced zone to act as a single mass, in effect making a new shear plane further back and/or with a lessened angle. In theory, I believe as someone alluded to earlier, you could have a nearly vertical soil mass, with no connection, or with no wall in front of it even (similar to what is left behind the fallen section).

The wall to soil mass connection is holding the wall veneer to the soil mass and not stabilizing the soil per se. The wall itself would not be enough weight to hold back that amount of soil.

2) Agreed.

Adding more than one foot of drainage aggregate will put stress on the wall, as the weight of the stone and it's mass need to also be retained. There is no cohesiveness with loose stone.

So...are you saying that more than 1 foot of 3/4" clean is BAD for the wall?? And that 3/4" angular washed stone has NO cohesiveness??

If so, I would have to disagree on both counts. I have seen clean stone be nearly vertical after it was compacted and then cut back. Loose stone would have less cohesiveness, but still some.

Clay should never ever be used as back fill in any wall project. The back filling was done by bulldozer or whatever probably helped heave the wall forward. They should have trucked in suitable fill, such as bank run gravel, which is free draining and compatible. This wall looks pretty vertical. I bet the batter is less than 3 degrees. For that height, 12 degrees would be optimal.

Agreed on both points.

zedosix
07-19-2007, 02:06 PM
I saw a Allan Block wall job today that almost made me crash my truck. I didn't have my trusty camera, but I WILL take some pictures tomorrow. Wait until you see how some moron stacked these blocks up! OMG...it doesn't get any worse than this.


I wouldn't use allan block for a wall 1' high. That stuff is pathetic.

PatriotLandscape
07-19-2007, 04:41 PM
if there is grid involved with this wall (it looked like filter fabric at first glance) they are not installing it correctly during the rebuild or not using it at all.

grid should be installed in the same plane of the course it is installed on and that grid seems to be pitched from different sections. I can't really tell but it doesn't look like they are incorporating it into the new wall.

EgansCountryGardens
07-19-2007, 08:46 PM
Geogrid is not intended to be used as a tie-back to the soil. As a matter of fact, if the geogrid is installed and not tied into the wall, it should make no difference at all. If you take a 5 gallon bucket full of sand and tip it upsidedown, you will get a pile of sand shaped like an upside down cone. However, if you take sand, and lay it every two inches with a sheet of geogrid at every layer, you will get almost a full cube of sand. It stabilizes the soil so that it doesn't laterally migrate.

GreenMonster
07-19-2007, 08:54 PM
Geogrid is not intended to be used as a tie-back to the soil. As a matter of fact, if the geogrid is installed and not tied into the wall, it should make no difference at all. If you take a 5 gallon bucket full of sand and tip it upsidedown, you will get a pile of sand shaped like an upside down cone. However, if you take sand, and lay it every two inches with a sheet of geogrid at every layer, you will get almost a full cube of sand. It stabilizes the soil so that it doesn't laterally migrate.

1) Disagree. I thought it stabilized the soil by breaking the natural shear plane, enabling the reinforced zone to act as a single mass, in effect making a new shear plane further back and/or with a lessened angle. In theory, I believe as someone alluded to earlier, you could have a nearly vertical soil mass, with no connection, or with no wall in front of it even (similar to what is left behind the fallen section).

The wall to soil mass connection is holding the wall veneer to the soil mass and not stabilizing the soil per se. The wall itself would not be enough weight to hold back that amount of soil.



This is what I'm saying. So, why are the block manufacturers making claims that they have better connection to the grid via pins, lip, rock lock, etc?

Does it really even matter???? From what we're being told by NCMA, no, it doesn't.

As much as engineers have an uncanny knack for driving me crazy, I would actually like some engineer input on this.