2D seepage and flownets

Question 1

flow rate assumptions for 2D seepage

Answer 1

• water is incompressible
• no volume change in the soil mass occurs
• qin=qout

Question 2

potential function

Answer 2

defines set of curves where total head is constant (different value for each curve)

Question 3

Flow function

Answer 3

defines family of curves that each represent water flow path. Both represent seepage through soil with constant k

Question 4

solution methods (4)

Answer 4

• Mathematical closed form
• Physical models
• Numerical methods
• Hand sketching (when soil has constant properties, assume steady state conditions)

Question 5

Rules for drawing flow nets

Answer 5

1) define datum
2) boundary conditions
3) flow and equipotential lines do not touch or cross each other
4) lines intersect at right angles
5) network of squares

Question 6

seepage occurs from…

Answer 6

… high to low head

Question 7

small squares in flow net represent

Answer 7

regions with higher discharge velocity, shorter flow path = higher hydraulic gradient

Question 8

Piping

Answer 8

-can be assessed using flow nets
- compare critical i with actual i
- piping erosion will start at downstream end of a flow net
- as soil erodes, pipe propagates upstream

Question 9

piping mitigation

Answer 9

1) Lower upstream water level
2) Lengthen flow path
3) Add filler material (crushed stone or gravel with high k)