Seepage
Team members
 George Savvas - 21005742
 Rami Kaawach - 21054783
 Youssef Elsheriff - 21051726
Table 1a. – measured and calculated pressure heads
Points
Actual experimental
reading from standpipe
(Units + mm)
Measured pressure head
from standpipe reading
(m)
Calculated pressure
head from flow net
drawing (m)
A
0.5
0.0125
0.5
B
4 + 0.4
0.1040
4
C
5 + 15
0.1400
5.5
D
5 + 16
0.1410
5.5
E
2 + 35
0.0850
3.5
F
+ 28
0.0280
1
Table 1b. – derived and calculated pore water pressures
Points
Derived pore water pressure from
standpipe reading (kPa)
Calculated pore water pressure
from flow net (kPa)
A
0.1250
5
B
1.0040
40
C
1.4000
55
D
1.4100
55
E
0.8500
35
F
0.2800
10
Figure 1
Figure 2
Datum
Figure 3
Calculation of seepage and outflow velocity
Calculation of seepage velocity
25mm
Measured times
What are the differences between outflow and seepage velocity ?
Δ𝑡𝐴 = 33.97𝑠
 Through calculations we can observe that:
start
𝑣𝐴 & 𝑣𝐵 > 𝑣𝑎𝑣𝑒𝑟𝑎𝑔𝑒 𝑜𝑢𝑡𝑓𝑙𝑜𝑤
Δ𝑡𝐵 = 41.44𝑠
𝑣𝐴 =
50𝑚𝑚
= 1.472mm/s
33.97𝑠
𝑣𝐵 =
50𝑚𝑚
= 1.207mm/s
41.44𝑠
end
Calculation of outflow velocity
Figure 1 – Visual aid to help with
seepage velocity calculations
 Some of the possible reasons
behind 𝑣𝐴 & 𝑣𝐵 being greater
than 𝑣𝑎𝑣𝑒𝑟𝑎𝑔𝑒 𝑜𝑢𝑡𝑓𝑙𝑜𝑤 are:
 𝑣𝐴 & 𝑣𝐵 > 𝑣𝑎𝑣𝑒𝑟𝑎𝑔𝑒 𝑜𝑢𝑡𝑓𝑙𝑜𝑤
• Deriving an expression to allow us to calculate outflow velocity
𝑉
𝑄
𝑣= = 𝑡
𝐴 𝐴
500 × 103 𝑚𝑚
5.90𝑠
𝑣1 =
= 0.437mm/s
460 × 422𝑚𝑚
 Assumption that flow is
steady
500 × 103 𝑚𝑚
6.47𝑠
𝑣2 =
= 0.398mm/s
460 × 422𝑚𝑚
 Application of 𝑄 = 𝑣𝐴
3
500 × 10 𝑚𝑚
6.16𝑠
𝑣3 =
= 0.418mm/s
460 × 422𝑚𝑚
𝑣𝑎𝑣𝑒𝑟𝑎𝑔𝑒 𝑜𝑢𝑡𝑓𝑙𝑜𝑤 =
0.437 𝑚𝑚 𝑠 + 0.398 𝑚𝑚 𝑠 + 0.418 𝑚𝑚 𝑠
= 0.418 𝑚𝑚 𝑠
3
 Difference of cross-sectional
areas gives rise to this
difference
Calculation of porewater pressure
What assumptions are made prior to calculation
of the pore water pressure using the flow net ?
1. Porewater pressure & rates of flow do not
change overtime
2. Assumption that the retaining wall is fully
impermeable
3. When considering Bernoulli’s equation the
velocity terms are neglected
4. Datum is impermeable
Calculating elevation heads (𝑧𝑥 ) relative to datum
 Utilizing figure 3:
@B: 𝑧𝐵 =8m
@C: 𝑧𝐶 =6m
@D: 𝑧𝐷 =5m
@E: 𝑧𝐸 =6m
What is the difference between the calculated
and measured pore water pressures and why
could these differences arise ?
 Differences arise due to the
experimental & model results
considering different units
 Experimental error – Misreading
the meniscus of the stand pipe
Estimating total hydraulic head (𝐻𝑥 )
 Utilizing the following equation:
Δ𝐻𝑖 = Δ𝐻 (𝑁 − 1)
 Using the data from figure 3:
Δ𝐻𝑖 = 3.5𝑚 (8 − 1)
Δ𝐻𝑖 = 0.5𝑚

Calculating total head
@B: 𝐻𝐵 = 12.5𝑚 − 0.5𝑚 = 12𝑚 1 𝐸𝑄 𝑑𝑟𝑜𝑝
@C: 𝐻𝑐 = 12.5𝑚 − 0.5𝑚 × 2 = 11.5𝑚 2 𝐸𝑄𝑠 𝑑𝑟𝑜𝑝
@D: 𝐻𝐷 = 12.5𝑚 − 0.5𝑚 × 4 = 10.5𝑚 4 𝐸𝑄𝑠 𝑑𝑟𝑜𝑝
@E: 𝐻𝐸 = 12.5𝑚 − 0.5𝑚 × 2 = 11.5𝑚 6 𝐸𝑄𝑠 𝑑𝑟𝑜𝑝
Calculating pressure head (ℎ𝑥 )
Calculating pore water pressure (𝑢𝑥 )
 Utilizing the following equation:
 Utilizing the following equation:
ℎ𝑥 = 𝐻𝑥 − 𝑧𝑥
@B:ℎ𝐵 = 𝐻𝐵 − 𝑧𝐵 = 12𝑚 − 8𝑚 = 4𝑚
@C:ℎ𝐶 = 𝐻𝐶 − 𝑧𝐶 = 11.5𝑚 − 6𝑚 = 5.5𝑚
@D:ℎ𝐷 = 𝐻𝐷 − 𝑧𝐷 = 10.5𝑚 − 5𝑚 = 5.5𝑚
@E:ℎ𝐸 = 𝐻𝐸 − 𝑧𝐸 = 9.5𝑚 − 6𝑚 = 3.5𝑚
𝑢𝑥 = 𝛾𝑤 ℎ𝑥
@B: 𝑢𝐵 = 𝛾𝐵 ℎ𝐵 = 10 𝑘𝑁 𝑚3 ∙ 4𝑚 = 40𝑘𝑃𝑎
@C: 𝑢𝐶 = 𝛾𝐶 ℎ𝐶 = 10 𝑘𝑁 𝑚3 ∙ 5.5𝑚 = 55𝑘𝑃𝑎
@D: 𝑢𝐷 = 𝛾𝐷 ℎ𝐷 = 10 𝑘𝑁 𝑚3 ∙ 5.5𝑚 = 55𝑘𝑃𝑎
@E: 𝑢𝐸 = 𝛾𝐸 ℎ𝐸 = 10 𝑘𝑁 𝑚3 ∙ 3.5𝑚 = 35𝑘𝑃𝑎