Localized Soil Failure in Crib Wall 1

[Riggly]

I am seeking advise on the how to repair localized soil failure within crib walls.
The walls range in height from 11 ft to 22ft, and the soil is sloped behind the walls and rise several feet above the top of wall. Several localized areas within the walls have exhibited moderate to severe soil lost. Is there any means/techniques out there to replace the soil without tearing down the walls?
Is placing geofabric just behind the face of the wall in order to retain the soil acceptable?

Any thoughts?.

Thanks

 

[GOTEK]

Hi Riggly,

You don't mention the condition of your walls so I am assuming that you're walls are in good condition and you're only concerned with the loss of material in your crib wall.

How many cells have lost soil, i.e., is it localized or global? Where are the voids...is there a predominant level of the crib structure where the soil seems to be leaving? Have you examined the site to see if there are surface or groundwater issues? What is the degree of your backslope? Some preliminary ideas are to use shotcrete or flowable fill to fill in your voids, but you should examine the site for drainage (water) issues as well as stability issues first. Can you give us some more information?

To answer your last question, I believe that geotextile behind the cribbing would help sigificantly and if the structure was built today more than likely it would have benn specified. But simply placing geotextile behind the wall may not solve the real problem.

 

[Riggly]

Gotek,
Thanks for your input. I did mentioned that the soil loss was localized, but these losses have occurred in several cells at varying height along the walls. The cribs are intact. Does not look like there is a ground water issue. Our borings have disclosed groundwater at least 5 feet below the foundation in one of the walls. From my observation, part of the problem appears to be surface run-off.

The backslope is in the region of 2.5(horizontal): 1 (vertical). One of the walls also appeared to have failed due to a landslide (circular). This wall will be replaced. The site is wooded and difficult to access, and the existing wall is founded about 25ft down the top of the slope. There are neaby structures, including a one story building and a 4 story building within 75 ft of the walls.

 

[PEinc]

Is it possible that the crib walls were never completely and properly backfilled when they were built? Maybe the fill is just settling inside the cribs. If there is no settlement behind the back wall of the cribs, then the problem may be just the fill soil shifting into unfilled rib inside the crib.

 

[Riggly]

PEinc,
There is no apparent settlement within the cribs. The soil viewed from the face the cribs is fairly dry, and is predominantly sand, with little silt and some clay.

 

[PEinc]

Your original post said, "I am seeking advise(sic) on how to repair localized soil failure within crib walls" and " Several localized areas within the walls have exhibited moderate to severe soil lost" and "these losses have occurred in several cells at varying height along the walls." Well, where is the settlement or lost soil? You should try to better explain your problem.

 

[Riggly]

PEinc
The soil loss is from the vertical face of the wall.

 

[PEinc]

Can you install weep hole in the front, between ribs and then shotcrete a solid facing?

 

[GOTEK]

Riggly,

You say that the soil loss is from the vertical face and yet the soils are fairly dry. What is the composition of the soil lossed is it predominantly fines or is it similiar to the backfill material? What is the age of your retaining stucture? Would you consider facing the structure as PEinc has suggested? Does the backslope fill material over-top or lie below the horizontal timbers? If below then perhaps surface water could be infiltrating the soils at the face of the crib wall and exiting via the weakest link. You did mention that you thought there were surface water issues, perhaps the installation of a diversion ditch above the wall would help reduce the soil loss. I have installed these behind walls with "infinite" slopes of 1.5H to 1.0V.


When you say moderate to severe soil loss...how large are the voids?

If a replacement structure is being cosidered for the entire sructure,some structure types (other than crib walls)to consider are a soil nail wall (unless your fills behind the crib wall are consolidating then I would be concerned about applying a bending force to the nails)and maybe a soldier pile wall - which may blend well, aesthetically, into the existing timber crib wall. Both are cut-wall applications rather than fill walls, but research the benefits to your site.

 

[Riggly]

The loss soil is same as the backfill GOTEK, and the structure is about 10yrs. The backslope material over-tops the timbers, allowing surface run-off down the face of the wall.
PEinc suggestion, and the soldier pile wall sounds like viable alternatives

Most of the voids are in the region of 2ft wide and 1' to 1.5' deep. In one location the soil was completely washed away from the cribs and all the timbers were exposed. The was an underground drain pipe that daylighted directly over that region and was the prime cause.

Thanks guys.