Yes. As long as you follow the rules for drawing the flow lines and potential lines, the 'ratio' of the number of flow channels to number of potential drops should be approximately the same.
Yes, Nf is the number of flow channels; it is not usually given, but drawing the flow net with 3-4 channels usually works out. Fractional channels are also possible. The number of Nd will be determined by how well you follow the rules for drawing the flow net. Don't over think it - just draw!
Good question. There is not typically an allowable seepage rate, therefore we are not able to calculate a 'factor of safety' in the same sense we would for bearing capacity, or other geotechnical calculations. We would use the calculated seepage rate for something like selecting the capacity of de-watering pumps for a project - i.e. we would supply pumps that could keep up with the seepage we anticipate - and we might size the pumps 3-4 times what the calculations suggest. This would be the closest thing I could think of to a 'factor of safety' for seepage. Hope this helps!
Thank you very much for the video, But how can you predict water goes in a particular path in soil, At 5:12 you said that "water is going to go down then around the tip of sheet and go up" why does that happen
Thank you for the question. Water is 'driven' (i.e. - flows) from regions of high-pressure to low-pressure. The difference in the elevation of the watertable on either side of the sheetpile wall creates this pressure difference. The flow net is a way to predict the path that the water will follow. The flow net method is based on the assumptions that water does not 'cross-over' itself - it only flows in continuous 'parallel' paths. It is also based on the assumption that the flow into an 'element' of the flow nets equals the flow out of the same element. These assumptions come from the french mathematician Laplace - you can read more in any textbook or on the internet, if you are interested.
Believe it or not, any number of equipotential lines will work! BUT, you must follow the rules for drawing the flow lines and equipotential lines. If you follow the rules, the RATIO of the number of flow channels to number of equipotential drops should always be about the same regardless of how many lines you draw. Hope this makes sense. Thanks for the question.
So you can get a different answer by just choosing to draw a different number of lines? I don't buy it. lol I could easily see 2 or 3 people legitimately following the super-vague rules of drawing a flow net, and getting 2 or 3 different ratios of Nf to Nd.
This is a common observation made by students. If you follow the rules perfectly, everyone should get a value of Nf/Nd within +/- 10-15%. This kind of accuracy is well within the acceptable limits for geotechnical engineering. In fact, there is probably more uncertainty and assumptions in the value of the hydraulic gradient! Think about drawing twice as many flow channels...if you follow the "rules" you will need twice as many equipotential lines...and you'll get the same ratio!
Best video ever! Thank you kind sir ❤
You are most welcome!
Thank you for this video, this makes so much more sense! You are the best!
Glad it was helpful! Good luck in your course!
@@EngineeringEconomicsGuy Thank you sir!
Welcome back sir, thank you so much for the upload!
More to come!
@@EngineeringEconomicsGuy can't wait 😁
thanks for the video! About to start learning about this in class on Monday :)
Have fun!
Great video got a exam in this tomorrow, you answered some question my book couldnt :D
Excellent! Good luck!
we all have the same book
@@VaultDwellerOG braja das?
Thank you For sharing your knowledge. Very helpful.
Glad you liked it! Thanks for watching!
Super helpful, thank you!!!
You're welcome!
so drawing the flow nets is arbitrary? I can draw one with more drops or less drops?
Yes. As long as you follow the rules for drawing the flow lines and potential lines, the 'ratio' of the number of flow channels to number of potential drops should be approximately the same.
thank you so much ❤️,
so basically Nf= is most of the times given and it is no of channels? and Nd is basically up to us?
Yes, Nf is the number of flow channels; it is not usually given, but drawing the flow net with 3-4 channels usually works out. Fractional channels are also possible. The number of Nd will be determined by how well you follow the rules for drawing the flow net. Don't over think it - just draw!
very good helpful video
Glad it was helpful!
Thank you for the video. at the end we found the seepage rate but how can we compare it to allowable rate ? how can we use it for proof of safety ?
Good question. There is not typically an allowable seepage rate, therefore we are not able to calculate a 'factor of safety' in the same sense we would for bearing capacity, or other geotechnical calculations. We would use the calculated seepage rate for something like selecting the capacity of de-watering pumps for a project - i.e. we would supply pumps that could keep up with the seepage we anticipate - and we might size the pumps 3-4 times what the calculations suggest. This would be the closest thing I could think of to a 'factor of safety' for seepage. Hope this helps!
Thank you very much for the video, But how can you predict water goes in a particular path in soil, At 5:12 you said that "water is going to go down then around the tip of sheet and go up" why does that happen
Thank you for the question. Water is 'driven' (i.e. - flows) from regions of high-pressure to low-pressure. The difference in the elevation of the watertable on either side of the sheetpile wall creates this pressure difference. The flow net is a way to predict the path that the water will follow. The flow net method is based on the assumptions that water does not 'cross-over' itself - it only flows in continuous 'parallel' paths. It is also based on the assumption that the flow into an 'element' of the flow nets equals the flow out of the same element. These assumptions come from the french mathematician Laplace - you can read more in any textbook or on the internet, if you are interested.
How do I know how many equipotential lines to draw. Do I need to calculate each one?
Believe it or not, any number of equipotential lines will work! BUT, you must follow the rules for drawing the flow lines and equipotential lines. If you follow the rules, the RATIO of the number of flow channels to number of equipotential drops should always be about the same regardless of how many lines you draw. Hope this makes sense. Thanks for the question.
thanks that was beast
Glad you liked it! Thanks for the comment.
Thank you
You're most welcome!
thanks man that was great
You're welcome! Good luck in your course.
Thank you sir
Glad I could help!
@@EngineeringEconomicsGuy 100%
So you can get a different answer by just choosing to draw a different number of lines? I don't buy it. lol I could easily see 2 or 3 people legitimately following the super-vague rules of drawing a flow net, and getting 2 or 3 different ratios of Nf to Nd.
This is a common observation made by students. If you follow the rules perfectly, everyone should get a value of Nf/Nd within +/- 10-15%. This kind of accuracy is well within the acceptable limits for geotechnical engineering. In fact, there is probably more uncertainty and assumptions in the value of the hydraulic gradient! Think about drawing twice as many flow channels...if you follow the "rules" you will need twice as many equipotential lines...and you'll get the same ratio!