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Discussion Starter · #1 ·
Hi I'm new to this forum and I just have a project I am struggling with in the planning phase.

I have 3 tiered walls I need to build. The existing retaining wall made of railroad ties is degrading and about to fall over. Customer insists on segmental retaining wall but I have no experience in building them whatsoever. There is not enough space to maintain the 2-1 rule in between the walls. Lowest wall will be 3.5 ft. middle is about 2 ft. and the top wall is an existing solid concrete wall.

I plan to use Nicolock ALTA segmental blocks. I will use geogrid because the second wall is SLIGHTLY under the 2:1 rule (is geogrid even necessary?) Is this wall going to last and are semental blocks a solid option for this project? The alternative would be solid poured concrete blocks with rebars ect.

Thanks!
 

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Thorough investigation

I see in your photos, that a thorough investigation should be undertaken prior to any works(including pre-removal of materials)
1) small test holes augered or hand dug(1 shovel wide) just below the upper concrete block wall.(each end and probably center) To a depth to competent native material, - Rock, gravel, non-disturbed compact glacial till, un-disturbed compacted sands/silts.
2) also the same in each of the terraces (each end and probably center)
3) an evaluation of what is behind the cement blocks, the bearing load, the past history of what preparation was done before any construction work was done for this block wall and what-is-behind-it??? This is a wildcard that needs to be taken into the equation.
4) water drainage ;
a) upslope of the area and the home
b) ditches & culverts upslope of the home
c) home roof, patio and basement drainage and water discharge points AND any possible ground over-saturation from these points.

I do note that the slope materials to the side (that the failing wall is on) of the house look suspiciously like bulldozed or basement excavation waste, making even more important the correct knowledge of what is existing underground.

From the ground investigations a person knowledgeable in soils and water(surface and subsurface) will be able to make a recommendation to go forward.
If you send me photos of the soil samples I may be able to help you come up with an action plan. Eric
 

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Discussion Starter · #3 ·
Thanks!

Soil and drainage were exactly what I was worried about. I'll get those pictures up ASAP.
 

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Soil sample.

Soil sample.
Not great stuff! I am concerned. I assume you dug down to competent undisturbed native ground. How deep did you dig? Did you dig a number of test holes. Ideally you would make a record of each hole: depth, measurements of levels where the sub-surface materials change. and a photo of the hole that shows the sides of the hole, and the material at the bottom.

I see deformity in the wood retaining walls, I must ask again, what is happening with the cement block wall? Is it showing signs of cracking? signs of settlement?(differential settlement??), what is behind the cement block wall?? any signs of issues??
What about the house basement - any signs of cracks in the basement wall? basement floor? Is that end of the house showing any signs of settlement?. If you give me the street address I can look at the place on google earth and Google street map. Suggest you email me the information to keep it private. my user name at gmail.
reguards, eric
 

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Jsc711 -

The walls you are dealing with are very poor construction with no real design basic.

As an example, there was no vertical spikes (or not enough) to prevent the individual ties from moving horizontal. There were also no "dead men" back into the soil. This leads to a failure of scrap wood by just sliding laterally from the fine soil and water lubricating it.

A reinforced retaining wall would requre a lot of excavation and the construction of a rigid footing below your frost depth to prevent heaving and cracking - big $$$S! plus forms lumber will be required.

A segmental wall is suited well for this application because it has sufficient shear/lateral resistance for you height of wall. Normally, a retaining wall does not need real engineering unless it is over 4 or 5 feet high (or equivalent) and constructed according to a manufacturers recommendations. Locally, many cities and counties use segmental walls on maintenance, erosion controls, sidewalk widening and carry a small inventories at their storage yards. The crews use the manufacturers installation guides for crews. If engineering is necessary, the offices also use the major manufacturers guides.

Wall height is not a problem if it really engineered, which always requires the use of geo-grid to reinforce the soil into a unit - Think of it as similar to a dead-man cable attached to a large block of concrete or piling. The longest semental wall I've seen was about 10 miles long and varied from 2' to over 20' long with inside and outside curves and was made using units from one of the major segmental wall products that are really international in use.

It is important to use the right backfill immediately behind the wall with a sheet of landscape fabric to allow the water to be drained out of the soil without erosion. For soil, a mixture of a common clean crushed rock (1/2-3/4" or so) and some common concrete sand to provided some controlled filtering and prevents the fines from plugging the backfill.
 
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