Rataining Wall

[SKJ25POL]

I have a wall that is 14.5 ft tall and from base to almost mid-height behind it is "Blue Lime Stone" and from mid-height to top of wall is "Broken Lime Stone".
My soil mechanic knowledge is a bit rusty. Could someone kindly tell me that do I have any lateral pressure applied to wall?
Any of above mentioned items will exert any lateral pressure on wall? any other lateral pressures?

Thank you
Skj

 

[oldestguy]

I take it this "rock" has the wall built against it or close, with narrow backfill. Is this to be built or is it existing?

 

[SKJ25POL]

It is an existing wall. The wall is 40+ yrs. old.
I didn't see anywhere on drawings states about narrow backfill. It was said pour wall against existing limestone.

Is the "Broken Limestone" applying any lateral pressure?
Does the "Blue Limestone" apply any lateral pressure?
Anything else may exert lateral pressure from the "Broken limestone" and "Blue Limestone" may exert lateral pressure?

I included a pic of the wall drawing. Hope is displaying it here.

Thank you,
Skj

 

[MTNClimber]

Broken limestone and the soil above will likely apply a lateral earth pressure. Blue Limestone may apply a lateral earth pressure, or maybe not. It just depends on its condition, fracturing, and which way the joints are dipping. There's no drainage system in the sketch to protect the wall from hydrostatic pressure. The bedrock may be fractured enough to allow water to seep into the ground and allow hyrdostatic pressure to build up. I don't have enough information to provide you with any real numbers or recommendations. You should contact (or hire) the project geotechnical engineer to find out how to approach your situation.

 

[oldestguy]

So far so good. My bet is the rock stands by itself and any filling between rock and wall has the"silo" effect. Means little if any pressure on the wall. Drainage apparently is adequate with this history of no problems.

 

[SKJ25POL]

oldestguy (Geotechnical),
So does that mean I just have a lateral pressure due to "Broken Limestone" on the upper half of the wall?
Is the lateral pressure distribution of the "Broken Limestone" is like soil a triangular pressure zero on top wall and max on the midheight?
Shall I not consider a saturated gama for Broken limestone since is draining well?
I appreciate if somebody can draw me the load or loads on this wall.
Thank you for your help.

Skj

 

[MTNClimber]

There’s a lot of information missing. Let’s start here, why are you trying to analyze the existing structure and why isn’t there a geotechnical engineer involved?

 

[SKJ25POL]

What information are missing?
I appreciate letting me know. Did I miss providing any information being asked?

 

[MTNClimber]

You should always provide context when possible. The information that I think is currently missing:

1. Why are you trying to analyze the retaining wall? (Is it to be replaced? Is this a school project?, ect.)
2. Why isn't there a geotechnical engineer involved on the project?
3. What is the structure for?
4. What is the current condition of the structure?
5. Is there any boring information?
6. How tall is that embankement on top of the broken limestone?

 

[SKJ25POL]

1. Why are you trying to analyze the retaining wall? (Is it to be replaced? Is this a school project?, etc.)
For maintenance and check. No is Not a school Project and I am not a student.
2. Why isn't there a geotechnical engineer involved on the project?
Its not any construction involved. I just check the wall.
3. What is the structure for?
Water.
4. What is the current condition of the structure?
Seems ok.
5. Is there any boring information?
Didn't find the old one.
6. How tall is that embankement on top of the broken limestone?
There is not any embankment on top of broken limestone seems they didn't put it or been taken off.

Maybe I should not posted my question here. Seems I am in a wrong territory. My apology.

 

[PEinc]

You are not in the wrong area. It is just that your question about lateral pressure from rock is not easily answered. The rock pressure could be very little to none or, based on inclination of sliding surfaces, it could be great. Without better rock information, determining lateral rock pressure would just be an educated, conservative guess.

http://www.PeirceEngineering.com

 

[oldestguy]

What do you mean the wall is for water? Is there going to be some change that will make this area likely to have more surface water coming from above?

Even if there is no new work, the geotech is needed to really answer your questions, even it no new work.

Let' say that upper rock stood there before the wall was built or at least did do for a short period. Clarify what the site was before the wall was built.

By the way you are not using terms that we use to describe the rock. A geologist likely can clarify the condition. I'd take the term "broken limestone" to mean it was once blasted and just is a pile of loose rocks.

 

[MTNClimber]

Sounds like this is a water tank of some sort. If you're just checking the wall then I would first take a look at its current condition. Are there any signs of distress? If not, then I would run a couple of scenarios to check the factor of safety. If you do see distress and there are unwanted affects from the tank walls failing then consider hiring a geotechnical engineer to help assess the situation.

For now, scenarios should be ran with the tank empty and add any surcharge loading that is applicable. I would first assume the blue limestone is stable and doesn't provide any load on the wall and the broken limestone will have a friction angle between 28 and 32 degrees. If factor of safety is satisfied then proceed to check if the blue limestone is not stable and give it a friction angle of between 30 and 36.

After running these analyses see which likely corresponds to your visual assessment.

Sorry for the back and forth, it's just the context matters to me in these situations. There's a lot of assumptions to this situation. If there are serious consequences to the wall failing, please seek out help from a local geotechnical engineer to help eliminate some of these assumptions.

 

[oldestguy]

Is this the side of a round tank, then a whole different picture is present. If concern is that the "wall" might cave in, then the arching of tank walls comes in as resisting pressures from outside.

 

[cvg]

[ul]
[li]Is the "Broken Limestone" applying any lateral pressure?[/li]
[li]Does the "Blue Limestone" apply any lateral pressure?[/li]
[li]Anything else may exert lateral pressure from the "Broken limestone" and "Blue Limestone" may exert lateral pressure?[/li]
[/ul]

without any geotech/geologic data, strictly speaking there is absolutely no way to know what the lateral loading conditions are. if you are going to make assumptions, best to get a local geotech to make them.

 

[darthsoilsguy2]

does it check out if you assume all heavy and saturated soil against the wall. The contractor would have had no obligation to leave any limestone there. you don't need geotech for a 1st pass at the comps if it checks out under those conditions.