Retaining Wall for Landslip
Retaining Wall for Landslip
(OP)
Hi,
I am looking at a job on a moderately steep slope (1V:2H) where a road was cut along the contours along the boundary line. The cut apparently stayed unprotected and during heavy rains a land slip occured along a portion of the cut into the neighbouring property.
I'm looking at advising the following
1. Remove of all slipped and loose material
2. Cut a horizontal bench the across the base of the slip surface
3. construct a retaining wall at the base of the cut along the boundary to the height of the previous ground level
4. Reconstructing the land behind the retaining structure to its original slope of 1V:2H.
My logic being that we would essentially recreate what existed before the land was cut and the retaining wall would be designed to support the sloping backfill. Does this seem logical and practical?
Are there any other reasonable solutions?
From an overall stability point of view is it logical to conclude that the construction of the 1V:2H embankment against the existing slip surface will give an overall factor of safety similar to what obtained before the slope was the cut and before the slip occured?
Thanks
I am looking at a job on a moderately steep slope (1V:2H) where a road was cut along the contours along the boundary line. The cut apparently stayed unprotected and during heavy rains a land slip occured along a portion of the cut into the neighbouring property.
I'm looking at advising the following
1. Remove of all slipped and loose material
2. Cut a horizontal bench the across the base of the slip surface
3. construct a retaining wall at the base of the cut along the boundary to the height of the previous ground level
4. Reconstructing the land behind the retaining structure to its original slope of 1V:2H.
My logic being that we would essentially recreate what existed before the land was cut and the retaining wall would be designed to support the sloping backfill. Does this seem logical and practical?
Are there any other reasonable solutions?
From an overall stability point of view is it logical to conclude that the construction of the 1V:2H embankment against the existing slip surface will give an overall factor of safety similar to what obtained before the slope was the cut and before the slip occured?
Thanks





RE: Retaining Wall for Landslip
RE: Retaining Wall for Landslip
I normally would but I am located in a very small island where geotechnical engineers really do not exist. Even engaging Civil/Structural engineering for a job like this is uncommon. (probably why the slip in the first place)
Because of the size of the slip....just over 7m along the cut, it would be difficult for me to advise to the client to fly in a geotechnical engineer from abroad. I would like to advise something conservative but not over the top that can't be explained logically.
Do you have any comments regarding construction of the embankment as I outlined in my original post?
Thanks
RE: Retaining Wall for Landslip
RE: Retaining Wall for Landslip
Keep in mind also that you only know that the slope failed. You don't quite know whether it was a rotational failure or a wedge failure. For example, is there some underlying horizon of clay that is providing a horizontal base to the sliding surface?
There are several methods to stablize slopes. A retaining wall may be one choice, providing you can demonstrate that the post-corrective-action geometries provide a safety factor of 1.5 or such.
You can also consider soil nails or flattening the original 2H:1V slope (or other such modifications to the original grading plan. All this is make-believe stuff when there is no knowledge of the soil strength parameters that'll govern design. Also, at this point, there is limited data on the underlying geology (i.e., depth and attitudes of layers).
These are not shade-tree geotech problems!
f-d
¡papá gordo ain't no madre flaca!
RE: Retaining Wall for Landslip
RE: Retaining Wall for Landslip
The failure is not a deep seated rotational but more translational. The soil is residual but sits on a compacted rock of tuff consistency. Its not a very hard rock but is generally stable throughout the island and on the rest of the site. The cuts were not left vertical but where battered to about a 1:1 slope. It seems like a larger pocket of residual soil existed where the slip occured. I was not on the job prior to the slip so I can't tell what happened. I do know that it was torrential rains over several days that caused the slip.
Its not common to build retaining walls along roads but slip has gone into the neighbouring property and the owner is making a big deal.
I was hoping that reconstructing the slope behind the retaining wall to its previous slope 1:2 would be atleast result in a similar factor of safety of what existed before so that I would not have to do a detailed slope stability analysis. (tedious to do by hand and not really my expertise)
I would have thought that it would be essential to create benches across the slip surface to allow for the proper compaction of the backfill.
Any other thoughts?
TT
RE: Retaining Wall for Landslip
Simple slop stabilizing techniques shall be considered. also drainage is a critical aspect of success.
RE: Retaining Wall for Landslip
RE: Retaining Wall for Landslip
RE: Retaining Wall for Landslip
RE: Retaining Wall for Landslip
1. if water is still seeping / running between the layers you really do not have a whole lot of time to work as the soil is likely to move shortly after you expose it. If so, providing drainage at a distance upwards becomes necessary.
2. if you have access to rock blocks say 1m x 1m or 1m 2m, you can design a gravity wall which is quick to construct, stable and self draining. This approach has been proven valid on several jobs we have designed on of which is 11 to 19m high. for added stability, you can slope the wall back while providing a base about 70% (or better) of the height.
depending on the amount of water present bewteen the layers, you may still be able to apply this aproach but you'll have to do it strips of 3m or so just to limit the risk of new slippage.
RE: Retaining Wall for Landslip
I'd suggest diversion ditches as high up the area as possible, even on the neighbor's land if possible. If that is done "properly" you may not need a wall after all. In your efforts, put most effort on this aspect.
In some cases a diversion of ground water seepage also is needed, with sub-drains in the soil above the slope, diverting that water slightly sloping, parallel to the contours. I use this method frequently for failing slopes and it works. Fill the trench above the pipe with concrete sand, not gravel or rock since they are not filters for soil and will plug up.