I'm trying to calculate the piping FoS and heave from a flow net.

I've attached the below but it was a quick sketch just to lay it out (please ignore scales/accuracy etc. - I did this for the purpose of this question). There's no sheet pile or toe in the embankment, though the embankment will be keyed in by 300mm. Embankment footing is about 4m in length. Unit weight = 20kn/m3. 1.5m from GL to impermeable layer.

flow net sketch.jpg

1) I believe with regards to piping - I need to measure my last "square". However, as you can see - I appear to have done something wrong with my last square. Would love to know what I've done if anyone has suggestions (may be to do with not including the keyed in section?)

2) I really am lost with the heave calculation. I have an old uni note to say the width is 0.5d. However, I can only find examples of d with regards to sheet piles (depth to bottom of sheet pile) - I don't understand how to do this with an embankment. Also I've seen equations to calculate i but again - I'm lost as to whether you calculate this using d (depth) or l(length i.e. 4m).

Apologies if this is obvious - it's been a long time since I even looked at this stuff and doesn't seem as obvious as it once did. Anything anyone has to explain this to me would be very much appreciated.

Thanks in advance