Q4 - Flow

Question 1

What is the formula for average velocity? v

Answer 1

v = k*i

Where k is permeability in m/s
i is hydraulic gradient

Question 2

What is the formula for hydraulic gradient? i

Answer 2

i = delta H/L

Delta H is the total change in head
L is the distance between point A and B

Question 3

What is the formula for permeability k?

Answer 3

k = Q/Ai = (QL)/(A*delta H)

Where Q is the flow rate
A is the cross sectional area
i is hydraulic gradient
Delta h is total change in head

Question 4

What is the formula for Flow Rate Q?

Answer 4

Q = A*v = A * i * k

Where A is the cross sectional area
v is the average velocity

Question 5

What is the formula for seepage velocity Vs?

Answer 5

Vs = v/n = (k * i)/n

Where v is the average velocity
n is the porosity

Question 6

What is the formula for porosity n?

Answer 6

n = Av/A

Where Av is the area of voids
A is the cross sectional area

Question 7

Give the three formulas for effective stress (sigma’) for upward flow, hydrostatic, and downward flow

Answer 7

Sigma’ u = gamma’ * z - gamma w * i * z

Sigma’ h = gamma’ * z

Sigma’ d = gamma’ * z + gamma w * i * z

Question 8

What is the process for seepage under a dam? Ie flow net, calculate flow q, and pore water pressure at A and B

Answer 8

1. Draw 3 flow lines Nf, then the equipotential lines Nd (like 14)
2. q=kiA=k * (deltaH/Nd) * Nf
3. Find the pressure head hp at both A and B:
   hpa = Ha - hea: where Ha and b is the height of water? I ACTUALLY DONT KNOW
4. Pa or b (kpa) = hpa * gamma w