Modeling of Reinforced Concrete / Concrete in Stability Analysis

[Adeel7]

I am using Slide v 6.0 and Geostudio 2004. I am facing problems in modeling of concrete. I have modeled concrete as a material both on slope and as a retaining wall. Is this a right approach for stability analysis or any other possible means for that. Any related information would be helpful.


Thank you

 

[PEinc]

This has been discussed previously. Try a search on the topic.

http://www.PeirceEngineering.com

 

[Adeel7]

Thank you PEinc.

Though i have searched previous topics but still i can't find clear answer. Actually, on slopes concrete may not act in a way as we modeled. How software develop/considered bond between two surfaces. I am attaching herewith sketch showing my area of concern.

Thank you

 

[PEinc]

thread274-162835

Try this thread for some discussion.

http://www.PeirceEngineering.com

 

[Adeel7]

Thanks

The mentioned thread (closed) is very helpful.

I would like to mentioned some points stated by GeoPaveTraffic.

"I agree that any structure must be designed for the forces that act on it. However, I do not in general believe that a slope stability program can be used to determine those forces. The exeception is when you have an active slide, i.e. F.S.=1.0. Under those conditions the stability program can be used to determine the forces acting on a stucture being constructed to stabilize the slide."

My stability analysis indicates F.S below 1 without concrete. How can i determine the forces against which i should design concrete for the portion as mentioned in previously attached file. Let me show another sketch showing some forces obtained from Slide to get higher F.S, is this is correct approach to design the concrete i.e along slopes approximate 70KN/m2 and on vertical facing 140 KN/m.

Thank you

 

[PEinc]

Here's the other thread I was thinking of.

thread260-277352

http://www.PeirceEngineering.com

 

[Adeel7]

Thank you very much. Deep Excavation Analysis thread will hopefullt serve my purpose.


My situation is that i have to stabilize the slope for long term conditions by providing concrete mat as without that it won't be stable.

I will use following approaches for analysis:

1. I will use less cohesion value i.e around 500 kPa
2. I will try to see the results by providng concrete weight surchage.

Thank you

 

[SixDegrees]

In slope stability I'd model the concrete using self weight and shear strength of the concrete.

The shear strength of un-reinforced concrete is about Sqrt(Compressive Strength).

I'd run the analysis with and without the shear strength of the concrete (but use the weight).

 

[PEinc]

500 kPa = 10440 psf, which is close to what SixDegrees is suggesting. I think that is too high. I would try a lower "cohesion."

http://www.PeirceEngineering.com

 

[Patgeotech]

A little late with my comment - why not introduce soil nails onto your slope? or tieback wall at the toe of the slope?

Your conhesion is a bit on the high side - if you have profiles on the rock, I find that Roclab (by Rocscience) is a good way to check your soil parameters. Could be handy with future projects.

 

[dgillette]

Can you really mobilize the shear strength of the concrete? Wouldn't the slide want to go over the top of the concrete, or else push it along, sliding on whatever it bears upon? A slightly deeper circular slide might just lift it, instead of shearing through it. SixDegrees' suggestion to run the analysis with weight of concrete only would provide a lower bound on FS.

(I made a similar comment on that other thread.)

 

[PEinc]

You are not trying to mobilize the shear force of the concrete as much as trying to force the slip circle around, but not through, the concrete wall.

http://www.PeirceEngineering.com

 

[dgillette]

Right, that's how it needs to be, PEinc, but his second drawing (resembling my tie-dyed shirt) showed his critical circle apparently trying to go through the concrete, not over it or under it.

 

[PEinc]

So where's the concrete in the 2nd picture????

http://www.PeirceEngineering.com

 

[dgillette]

It's not that white box wherein it is written "140.00 kN/M" (sic)? I had thought the right side of the box is the material boundary, but upon zooming in on it, it looks like that could just be dimensioning, and not a boundary.

 

[PEinc]

"I have modeled concrete as a material both on slope and as a retaining wall."

Maybe the 140 kN/m (or kN/m^2?) and the 70.0 kN/m^2 represent surcharges from concrete that has not been drawn in the picture?

http://www.PeirceEngineering.com

 

[PEinc]

If so, shouldn't the 70 kN/m^2 be oriented in the vertical (gravity) direction?

http://www.PeirceEngineering.com

 

[dgillette]

Or maybe the lateral pressure of 140 represents the sliding resistance of the concrete on its foundation. Correct, PE, if what's on the slopes is the concrete's dead weight, it should be vertical.

If I have done the numbers right, 70 kN/m2 is the weight of about 3 m of concrete (3 m * 2.4 tonne/m^3 * 9.81 m/s^2).

Adeel7 - Are you still there? Please explain the pressures.

 

[PEinc]

3 meters is a lot of concrete surcharge- and probably not very economical.

http://www.PeirceEngineering.com

 

[Adeel7]

Thank you every one for nice discussion.

Yes in second pic no concrete is modeled as layer. You are right that 70 KN/m2 should be vertical as concrete weight will acts in vertical direction. But it will destabilize the slope. Thats why I have modeled it normal to the slopes which simulates to some extent the anchors.

At the bottom i have tried to used point load of 140 KN/m (equivalent to the resultant of a wall) or Uniformaly distributed load can be used.
I think by this approach, we can atleast get pressures or in simple means its a back calculation. So we can try to stable the slope by providing surcharge and then design the concrete/anchors etc according to it.

@ PEinc. 3 meter concrete is uneconomical option thats why this may not be a good solution for such stability problems. What i finally decided is that i go with combination of some backfill and retaining wall. Though it is still uneconomical but depending upon the importance of the project. Its Ok.