Segmented wall failure in VA

[CM1995]

This is going to be expensive -

http://www.wset.com/story/24424658/...ne-wall-gives-way-at-south-peak-in-roanoke-co


From looking at the pictures I have a good idea what one of the causes of failure is, curious to see what others think.

 

[51kw]

Hydraulic pressure from water trapped behind it.

 

[dirtmonkey]

No drainage.

 

[Steve Frazier]

Ditto above. A good portion of my business was to install walls of this type and I received factory training to do it. They prescribed that there should be perforated pipe at the bottom of the wall run to daylight at some point with a 1' minimum depth of clear stone directly behind the wall protected by geotextile.

 

[Turbo21835]

It certainly looks like a lack of drainage issue. But if you look, there is geotextile fabric in those pictures. This leads me to believe there may have been some stone in there too. Not sure on drainage. Not sure what the weather was like down there, but I wonder if its been cold and there may have been some freeze issue that compromised some construction/material/design defect?

Now the bigger question is what would you do to fix this? I cant imagine trusting what is there and rebuilding it. I also cant imagine removing everything and starting over. Seems like it would make more sense to build a new wall in front of the old one and fill with stone?

 

[CM1995]

Lack of proper sized stone backfill behind the wall and hydraulic pressure looks to be one reason the wall failed. However notice just the top portion of the wall fell. The picture shows some stone backfill in the reinforced zone directly behind the wall, maybe 4-6'.



I had my suspicions that the water behind the wall that caused the issue, came from a storm pipe above. If you notice there is not much shoulder between the curb and the wall, not a lot of room for a large amount of water to enter behind the wall.

There were two MSE walls that failed in the Birmingham area at two different shopping centers. One of the failures was due to a storm pipe that settled where it entered a stacked manhole, behind the wall. The water obviously leaked from the pipe and went directly behind the wall. The loading dock for the Circuit City settled about 4' due to the failure.

Hayward Baker spent several months at that site, stabilizing that wall and they are currently working at the other site stabilizing a JC Penny. There is no telling how much that cost..

It seems a storm drain failure might be the culprit here as well - http://www.wdbj7.com/news/local/tra...ng/-/20128466/23883306/-/qk822qz/-/index.html

I don't buy the "pressure in the pipe" pushed against the wall. There was a bad connection that allowed the storm water to exit the pipe and saturated the material behind the wall.

The last major Keystone wall I built was 15' high at it's tallest and 187' long. We installed a sheet drain between the existing fill and the reinforced zone. The reinforced zone was entirely backfilled with #57 stone, horizontally 20' in some places. Proper draining is the life of these walls and special care needs to be taken when running storm sewer within the reinforced zone.

There is no way I would have built that wall without having at least 10-15' of stone backfill horizontally behind it.

 

[nedly05]

Im thinking its a lack of drainage. If there was crushed stone back there it seems as though we should be able to see some sign of it. Glad I'm not responsible for that mess, its definitely going to be expensive to fix!!

 

[CM1995]

Now the bigger question is what would you do to fix this? I cant imagine trusting what is there and rebuilding it. I also cant imagine removing everything and starting over. Seems like it would make more sense to build a new wall in front of the old one and fill with stone?

Good question and topic of discussion.

I would be inclined to repair it, after all the site assessments have been made. If the bottom portion of the wall is in good shape, excavate the upper portion carefully and rebuild that section. If the storm pipe was the culprit, then a thorough investigation of the integrity of the storm piping close to the wall should be done and repair that first.

Any manholes and storm piping adjacent to the wall should have had mechanical or concrete restraints to keep any pipe connections from settling, something we don't do when laying normal storm piping. Encasing the RCP in flowable fill or concrete close to the wall might have prevented this from happening.

If you think about it, if they just laid the RCP like normal - rubber gaskets, bell and spigot, and joint number 2,3 or 4 out of the manhole settled enough to allow water to leak out, that would be more water than the wall is designed to drain in a concentrated area.

Whatever happens, this is a very expensive failure that needs to be used as an educational tool for anyone doing this sort of work.

 

[CM1995]

My suspicions are confirmed -

Roanoke Co., VA - Engineers say they know what caused a retaining wall to fail over the weekend near 220, leaving quite a mess on a high profile development being built near Tanglewood Mall.

It happened Saturday soon after heavy rains hit the area.

Luckily no one was hurt, but there are a lot of people wondering what exactly happened.

The engineer who designed the wall at the South Peak development says the partial collapse was apparently an issue that had been developing unbeknownst to anyone, until about 800-square feet of that wall gave way.

The primary factor, according to an engineer, was an improperly installed drainage pipe that has been seeping water for some time.

The problem caused the wall to separate from the geo-grid that holds the wall in place.

That separation was exasperated significantly during Saturday's downpour.

"There was a separation between the curb and gutter and the asphalt pavement that occurred, I believe, after the initial movement of the wall and opened a gap allowing more water to get in there," explained GeoTech Engineer Mike Circeo.

"Things like this happen. Especially when you are dealing with a project of this size and complexity of this one. We're dealing with it the right. While we fix it we will continue to develop the other aspects," said South Peak Developer Hunter Smith.

The rest of the wall has been inspected, ABC 13 has learned, and there are no other issues from what engineers can tell.

While crews are reconfiguring parts of the drainage system, ABC 13 is told the repair to the wall itself will take about two weeks to complete.

http://www.wset.com/story/24437949/...alled-pipe-caused-wall-collapse-in-roanoke-co

ROANOKE COUNTY, VA -
(story has been updated with information from Roanoke County and the project engineer)

We are continuing to follow the South Peak Development wall collapse that happened Saturday, shutting down traffic along US 220. No one was hurt.

The project engineer Mike Circeo with Circeo Geotech says the wall collapsed because of a storm water pipe that was leaking. The water forced the wall out but he says it's more of a cosmetic issue than a structural one.

"The wall itself I think is designed to withstand a certain amount of water that seeps in behind it but when you have a concentrated flow like this there really isn't any way to plan for that. You just need to make sure that work is being done properly so they don't continue to lose water outside the pipe," said Circeo who has been with the project since the beginning.

Engineers, developers and inspectors from Roanoke County and the project have been at the site since Saturday afternoon when this all happened.

Right now Roanoke County tells us they are waiting for a written report from the engineer but says drivers shouldn't worry.

"Certainly it looks like a safety issue but this right now is an active site, meaning construction will continue to take place. that issue it's just the cost of doing business it can be repaired," said Tarek Moneir, the Roanoke County Deputy Director of Development Services who oversees engineering for the county.

Cireco says there could be other pipes affected. There are eight retaining walls and storm pipes between most of the walls. Each pipe will have to be inspected. Cireco says the only way to do that is by a camera. The pipes are all buried six to twenty feet in the ground. If other pipes need to be repaired they can put in a pipe liner instead of digging up the wall.

"The site's been inspected both by the public and private sector. The walls have been engineered. It's an unfortunate event, things like this happen but the only thing that you can do is fix it and move on," said Hunter Smith, the president of Smith/Packett, the South Peak developer.

We've requested inspection reports but haven't received them yet. Meanwhile Roanoke County tells us to their knowledge nothing ever came up as an issue in past reports.

http://www.wnct.com/story/24434051/south

 

[td25c]

I agree about drainage and proper backfill stone. We have to do the same on poured concrete walls or they can fail. Not being familiar with this block system I first assumed the fabric we see still hanging in the picture was geotextile cloth laid against the inside of the block. If I understand correct this is actually "geo-Grid" that is installed in the fill every so many feet with the outer edge tying into the block for support ? www.keystonewalls.com/media/Technotes/bckfllmvmnt.pdf

Interesting product www.keystonewalls.com/media/Literature/CS0950-RockyMtAirport.pdf

 

[CM1995]

Not being familiar with this block system I first assumed the fabric we see was geotextile cloth laid against the inside of the block. I understand correct this is actually "geo-Grid" that is installed in the fill every so many feet with the outer edge tying into the block for support ?

That's geogrid which is different from woven and non-woven geotextile cloths. It's specified at a certain interval horizontally, so many courses of block and gives the wall it's "hold back" strength. It's attached to the blocks with fiberglass pins and rolled out to the designed length in the reinforced soil zone. Some manufacturers use different styles of anchorage to the blocks, not just fiberglass pins but the walls I have built have all been designed that way.

 

[Hitachi225]

Any idea what a repair like that would run? probably close to the original cost of the wall , if not more?

 

[td25c]

Thanks for the answer CM. My only experience with block walls were the smaller blocks that had a lip on the inside to lock each row together and we weren't going very tall with them so no tie system was used.

Back to the wall failure in VA. Is it possible they are pushing past the limits of the product ? Man that wall looks 25 to 30 feet tall ! I just wonder even with proper drainage & backfill if the plastic geogrid tie system might still deteriorate & fail over time.

 

[CM1995]

Back to the wall failure in VA. Is it possible they are pushing past the limits of the product ? Man that wall looks 25 to 30 feet tall ! I just wonder even with proper drainage & backfill if the plastic geogrid tie system might still deteriorate & fail over time.

I tend to have that same train of thought TD, although my skepticism of the wall system would be how the geogrid is anchored to the blocks. A wall that tall has many opportunities for connections to fail. In my opinion, the geogrid would last longer than the life of the wall, buried in the ground away from sunlight.

The weakness I see is the connection point to the blocks, if this connection is not kept then one just has a wall made of stacked CMU blocks.

 

[Steve Frazier]

I worked with Unilock Pisa II, it has a cast in keyway system to hold everything together. I did a wall with the brand pictured here once where the homeowner had already purchased the block, I didn't care for the plastic pin system. You were supposed to fill the voids with pea stone as well to give the wall some additional mass. Unilock is a solid concrete block. The geogrid resembled a snow fence, on walls over 4' high they were required to be engineered, which was provided free of charge by Unilock. The geogrid has fiberglass strands running in one direction, the other part of the grid is just a textile to hold the fiberglass sections at the proper distance. It's imperative that they are not confused or the wall will fail. The mesh was laid over the prescribed course of block almost all the way to the front of it so the grid was pinched in the keyway. The weight of the upper courses held it in place and it went back into the backfill a prescribed distance with compaction.

Behind the wall was the clear stone I mentioned that had a layer of filter fabric between it and the backfill to keep the backfill from migrating. It was a fiberglass felt product.

 

[td25c]

This may not be a good comparison CM. But I have seen plastic field tile go bad over the years. Farmer called & said he had some sinkholes in the field so we took the skid loader & hoe to investigate. We found the plastic tile broke about every 16 to 18 inches . The whole dam field was like that. Farmer ended up re-tiling the field. I always thought plastic was good forever if kept out of sunlight. This tile would have been first installed in the late 1970's. I know plastic has come a long way sense then but on a big tall project like the block wall in VA. I would still question it. Like my dad always said..... "If you want something to last.... Build it out of concrete & steel".

I'd be a nervous wreck working on the a project like the wall in VA relying on plastic to hold it all up. Heck .. even on a 4' tall concrete retaining wall I put a deadman in every 25 to 30 feet with drain tile cast in it. I'm old school & skeptical

 

[wnydirtguy]

I would agree on lack of drainage. on a wall that tall I would have considered put more drainage pipes in. Maybe one at the top for ground run off and half way down. In a time of a lot of rain it would take awhile to drain the water to the bottom and out a 4" pipe.

 

[qball]

Sheet pile and tie-backs. Tear out that fragile block wall, call Hayward-Baker and have them drive sheets with tie-backs. They will last forever.

 

[CM1995]

TD25C the geogrid spec'd in these walls is tough as nails and not your normal plastic.

Geogrids are commonly made polymer materials, such as polyester, polyethylene or polyproylene. They may be wovern or knitted from yarns, heat-welded from strips of material, or produced by punching a regular pattern of holes in sheets of material, then stretched into a grid.

http://en.wikipedia.org/wiki/Geogrid

Some more information- http://www.nilex.com/book/export/html/22

Who knows at this point what type grid the engineer spec'd for this wall but I believe the grid didn't contribute to the failure -the leaking storm drain was the culprit. These walls are designed to handle water on top and behind them as a system but not designed to handle a point flow being introduced behind it.

 

[td25c]

Yeah CM , that's interesting about the geogrid and I agree its tougher than the plastic of yesteryear. Yes it's amazing how quickly moving water can under mine fill damaging a structure.

Hey... I think I found some overhead views of the wall & facility. Scroll down & check out the first photo under Residential updates October 2013 http://www.southpeak.net/photo-galleries/