HI-Help with Rocscience Slide

[jjgeotech]

I am just learning slide--I have a slope with some water input below surface that is resulting in a combo slump and earth flow. Anyone have any pointers on how to enter the water aspect correctly into Rocscience's Slide program?

Thanks in advance!

J J Geotech

 

[Gimbli]

In the Boundaries tab, you will find Add Piezometric line. You will be able to draw the grundwater surface along the path you want. There are some other alternatives to do it, such as using the Ru coefficient. Ru models the pore pressure as a fraction of the vertical earth pressure for each slice. Check the help menu, it is very friendly. You are even able to perform seepage analyses. I find Slide much powerful and useful than many other more expensive softwares.

 

[jjgeotech]

Thank you Gimbli! I also like Slide very much. I'm not sure which is the appropriate way to add the water--since I am not sure where it is coming from and what the residence time is. I figure since it is not truely a water table, maybe Ru is more appropriate--but here, I'm not sure what values to use for Ru..... I will investigate applying seepage. Thank you so much for your input-Back to Slide.

JJ Geotech

 

[kooko]

Totally off topic..but WTH.
When doing analysis for soils below water table, there is a option to include submerged unit weight. If its not selected the program assumes the total unit weight of soil. For pretty straight forward jobs like detention pond, it is professional practice to assume the submerged unit weight to be the total unit weight? Or should I make some kind of assumption for the unit weight based upon assumed specific gravity?

 

[Gimbli]

I would you use submerged since it is more conservative unless you are very confident in that the subsoil will not saturate ever because either you have an impermeable layer or something. But, as we say in may country there is nothing for sure but dead and taxes.

Are you using slide? Because I think that the option Slide offers is to which layers are to be considered saturated based on input GWT and then the program will compute the submerged unit weight.

 

[kooko]

how does slide calculate the saturated unit weight though? My understanding is that you have to either perform a specific gravity test, or make some kind of assumption regarding specific gravity right?
But what u said earlier about placing all layers below water table to be saturated..thats what I do. However, when I do use the saturated unit weight (which is higher), I typically get a lower F.S.

 

[Gimbli]

I dont think Slide will compute the saturated unit weight. Instead you will input it. If you do not measure unit weight directly from samples you need to estimate it with tables, empirical correlations, engineering judgement, etc.

You will get a lower factor of safety if the material exerting loads, lets say in the crest, is heavier.

 

[raj4civil]

I don't know is it the right section to send my enquiry.
I am modellings a slope excavation of 50-55 m high for putting up a hydro powerhouse in river bed material/alluvium. To reduce the quantity excavation i am modeling a cut slope (1 h : 1.5 v)with a bench of 5.0 m in every 10.0 hight interval and providing some high strength soil nails to achieve the allowable FOS.
For silde input the parameter for soil nail required,
1. axial tensile strength kn
2. plate capacity Kn
3.Bond/ Pull out strength Kn/m

What is the correct estimate of plate capacity (2).
what is the allowable FOS for normal/seismic condition for global stability of slope.
And for that allaowable FOS one should assume the allowable tensile strength or yield strength of the bar/nail??
Can this type of excavation be modelled in SNail software.
Help me if any one has the answer.

Regards

Raj

 

[Gimbli]

Raj4civil:

You should let a Geotech do the overall slope stability analysis