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Sunday, 25 March 2018

Stability Analysis of an Earthen Dam by Swedish Slip Circle Method | DHS termwork

I once read a quote from Terzaghi,
"Soil is the most complex material known to humankind"

Just as said it isn't easy to analyze the earthen dam for stability but its fun to play around when you have a lot of computing power at your disposal. Here is how we completed the assignment of analysis of an earthen dam, the Digital Engineering Jugaad Way!

Firstly, You need 2 software
1. Autocad
2. Mircosoft Excel (or any other spreadsheet software)

Then as per the given scenario, we made a dam Profile

Once you're done with the dam profile you can start with preparing the basic stuff for the phreatic line, in other words the parabola that governs the seepage

for plotting the directrix you need the relation ship between the waterline and the point A on the surface of the water.

Once you're done with establishing the above points you can more ahead on with the calculation of the phreatic line. And this is where excel kicks in and simplifies your task of getting things done!

We did a lot of trial and errors and finally realized that the origin for this co-ordinate system is at the foot of the core on the downstream side which is named as point F in our diagrams

Now once you're done plotting the phreatic line,
in the above figure the blue line is the phreatic line and area below the line is wet and above it is treated as dry

So now that the basic geometry work is completed you can proceed with the Swedish Slip Circle Method which is a process involving a number of steps

  1. Compute the centre for the arc
  2. Cut an arc
  3. Divide the arc into number of slices
  4. Find the centre of the slices
  5. Find the areas of the slices considering different areas for core, shell and foundation as well as saturated and dry areas
  6. Then continue with the calculations.
After cutting the arcs the slip circle and the slices will look something like above! Doesn't looks good? Add some Hatching to make it look better and easier to understand

That looks really awesome, we made a similar one for the upstream side as well...
But seriously all art works end now, time for some serious calculations.

With reference to the Book written by Dr. B.C. Punmia and guidance from Prof. N.A. Autade we created this spreadsheet and computed the stability for the downstream side.

So as we now that the template and the data ready for the downstream side, we used two shortcuts!

1. Using the mirror feature in AutoCAD and later verified if it was correct (this saved a lot of time & efforts)
2. Used the same template and just modified the areas according to the upstream diagram.

And for area computation, we use AutoCAD instead of the erroneous plannimeter to get precise readings. Check my video on how I used AutoCAD to estimate the dead load from a slab, the basic principle is same for estimation of the areas.

So now that we did all this on the computer, we were still required to plot the same on graph paper & that was a tedious task but with huge efforts we completed it.

I finally Made a video on the complete procedure, check it here

Download Center

Would Appreciate your comments!

Special Thanks to:
Prof. Nilima Autade
Er. Bhagyashri Gude

Here's a good video explaining the process,

Stability Of Slopes Of Earthen Dam - Dr.Sunil Kute

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