How to model the soil 1

[Lasa88]

I am designing a water retaining structure and I need to know how to model the soil under the structure to see the soil stresses. pl help me on this regards.

Thanks you in advance

 

[IJR]

Good question Lassa88

but there is no harm if you do a little theory yourself. You can APPROXIMATE soil by using springs.

The value of spring you should input into SAP2000 is calculated as follows

1-Determine the soil stiffness in kN/m3 or ton/m3 of lbs/ft3 whatever units

2-Multiply this by the area represented by the node where you want to put the spring, this gives you kN/m or ton/m or lbs/ft etc.

This is really a crude approximation and you wont get results more superior than you would get doing some manual calculations.

And there is a trap. If your spring reactions are negative, the model becomes wrong. Make sure you dont have spring reactions with uplift, since real soil can not tolerate that

And another trap: If your loads are seismic, spring stiffness determined above is questionable.

What elements will you use to model the tank? shell elements?


respects

ijr

 

[Lasa88]

IJR,
It is really helpful and as you said I need to study some text book. Yes, I have used shell element to model the Intze type tank. Anyway I have some questions on this regards and hope to come back soon. I hope you will help me again.
With Regards
Lasa

 

[par060]

you can use areas and then assign a spring stiffness to that area. You even can make the springs compression only...draw the area and then assign what you require

 

[iotoma]

Hey Lasa88,

I have recently encountered a similar problem with yours, modeling the soil in order to find out the stresses, and I did it using solids. I assigned the appropriate material properties to the solids and i was able to see the stress distribution after the analysis.
I might add it's a bit time consuming and I am still in the process of validating this approach.

Cheers,
iotoma