SEEPAGE ANALYSIS UNDERNEATH DIYALA WEIR FOUNDATION TERM PAPER PRESENTATION CEL-754 Geotechnical Processes in Rock Engineering Presented by: Saravanan Winfred George
2. Introduction The construction of Diyala weir commenced in
1966 and wascompleted in 1969. The structure includes a road bridge
and new canal head works. This structure is located 7km downstream
from the Hamrendam, approximately 130 Km northeast of Baghdad, near
the townof Sidor. The main purpose of this Weir is to divert
outflow of the Hamrendam to the Khalis and Sadr Al-Mushtarak canals
for irrigation. 3. Section of Diyala Weir 4. The Problem Seepage of
water is one of the major problems, which has an effectupon
hydraulic structures. Diyala weir structure is suffering from such
engineering problems.It was taken as a case study and it had been
checked against pipingand uplift pressure by using numerical model.
The effect of removing one of the three sheet piles rows wasstudied
and evaluated to investigate the quantity of seepage,
upliftpressure and expected exit hydraulic gradient for these
cases. 5. Input Data for Seepage Analysis Total length of a weir
foundation equals 24.5 m. Depth of 1st row of sheet piles (upstream
sheet pile) equals 4.5 m. Depth of 2nd row of sheet piles (middle
sheet pile) equals 2.5 m. Depth of 3rd row of sheet piles
(downstream sheet pile) equals 3.5 m. Unit weight of the soil
underneath Diyala weir equals 18 kN/m2. Permeability for clay soil
underneath Diyala weir equals 1e-5 m/s. Depth of impervious layer
below Diyala weir foundation equals 11mfrom the bed level (B.L).
Soil foundation underneath the weir is saturated, isotropic
andhomogenous. 6. Seepage Analysis by FEA 7. Seepage Analysis by
FEA (Contd.) 8. FEM Model Properties The Eight noded quadrilateral
elements were used to idealize thevertical cross section of
permeable soil underneath Diyala weirwith the following Mesh
Properties,Mesh type: gradedAnalysis Type: Plane StrainNumber of
elements: 1278 Solver Type: Gaussian Elimination Maximum Number of
Iterations: 500Number of nodes: 3989 Tolerance: 1e-006 9. Diyala
Weir Model in Phase2 with all Cutoff 10. Seepage Results from
Phase2 with all cutoff 11. 6.005.004.003.00 15.00 16.00 17.00 18.00
19.00 20.00 21.00 22.00 23.00 24.00 12. Uplift Pressure (Contd.)
The thickness of weir impervious floor at any point should notbe
less than 2/3 of uplift pressure. The required floor thickness for
points below downstream floorand the provided floor thickness are
tabulated below, 13. Uplift Pressure along Base Slab 0.00 4.00 8.00
12.00 16.00 20.00 24.0062.0063.0064.0065.0066.0067.0068.00 14.
Floor ThicknessDistanceFloor Elevation Total Pressure at Required
Floor Provided FloorUplift Pressure (m) Calculated by Diffalong D/s
(m) (m) Base (m)Thickness (m)Thickness (m) Authors0.00 61.50 68.00
6.504.33 - 6.001.671.00 60.50 66.05 5.553.70 - 5.922.222.00 60.50
66.03 5.533.69 - 5.581.903.00 60.50 66.01 5.513.67 - 5.241.574.00
61.50 65.51 4.012.67 - 3.911.245.00 61.50 65.50 4.002.66 -
3.580.916.00 61.33 65.47 4.142.76 - 3.410.657.00 61.00 65.43
4.432.95 - 3.410.458.00 60.67 65.36 4.693.13 - 3.400.289.00 60.33
65.27 4.943.29 - 3.400.11 10.00 60.00 65.17 5.173.45 - 3.40-0.05
11.00 59.67 65.05 5.393.59 - 3.40-0.19 12.00 59.33 64.92 5.593.73 -
3.40-0.33 13.00 59.00 64.76 5.763.84 - 3.40-0.45 14.00 59.00 64.61
5.613.74 - 3.06-0.68 15.00 59.00 64.46 5.463.64 2.492.73-0.92 16.00
59.00 64.33 5.333.55 2.412.50-1.05 17.00 59.00 64.19 5.193.46
2.342.50-0.96 18.00 59.00 64.06 5.063.37 2.262.50-0.87 19.00 59.00
63.91 4.913.27 2.222.50-0.77 20.00 59.50 63.81 4.312.87
1.932.00-0.87 21.00 59.50 63.73 4.232.82 1.892.00-0.82 22.00 59.50
63.66 4.162.77 1.852.00-0.77 23.00 59.50 63.61 4.112.74
1.832.00-0.74 24.00 59.50 62.05 2.551.70 1.002.000.30 15. Exit
Gradient (Contd.) The critical hydraulic gradient (icr ) was
calculated from, The unit weight of saturated soil underneath the
weir structure is18 kN/m2 and unit weight of water 9.807 kN/m2. The
calculatedvalue of the critical hydraulic gradient is 0.835. This
lead to factor of Safety against piping equals; The exit gradient
from the Analysis is 0.17, lead to Fs = 4.9. A factorof safety (Fs)
of 4.9 is considered adequate for the safe performanceof the Diyala
weir structure against piping 16. Exit Gradient Plot from Phase2
with all cutoffThe Exit Gradient Value from SEEP / W is 0.17The
Exit Gradient from Phase 2 is 0.18 17. Pressure Plot with No U/S
cutoff 18. Exit Gradient Plot with No U/S cutoff The Exit Gradient
Value from SEEP / W is 0.19 The Exit Gradient from Phase 2 is 0.24
19. Pressure Plot with No U/S cutoff 20. Pressure Plot with No
Middle cutoff 21. Exit Gradient Plot with No Middle cutoff The Exit
Gradient Value from SEEP / W is 0.17 The Exit Gradient from Phase 2
is 0.20 22. Pressure Plot with No End cutoff 23. Exit Gradient Plot
with No End cutoff The Exit Gradient Value from SEEP / W is 0.21
The Exit Gradient from Phase 2 is 0.25 24. Seepage and Exit
Gradient The below results of quantity of seepage and exit gradient
for eachcase as one sheet pile assumed to be removed.Without Ist
Sheet PileWithout IInd Sheet PileWithout IIIrd Sheet
PileDescriptionAuthors Ours AuthorsOurs Authors OursQuantity of
Seepage1.10E-05 1.33E-05 9.62E-061.19E-05 1.05E-05 1.31E-05 (m3/s)
Exit Gradient0.190.240.17 0.2 0.21 0.25Factor of Safety4.4 3.5
4.94.2 3.93.34 It is noted from the results of removing the first
sheet pile is moreeffective on increasing of seepage while removing
the third sheetpile is more effective on increasing of exit
gradient values but thefactor of safety against piping (Fs) for all
values represent safesituation. 25. Summary of ResultsThe following
results are obtained by using 2-D finite elementmodel of Diyala
Weir, Foundation of Diyala weir is safe against piping and any
excessiveuplift pressures. The defect in one or more of the three
sheet piles has causeddisplacement of the downstream floor (apron
slab), cracking inweir foundation and scour of soil underneath the
weir, due toincreasing the quantity of seepage, uplift pressure and
exitgradient. 26. Summary of Results (Contd.) Investigation of
failure leads to suspect that the sheet piles inupstream is
exposing, and could be corroded and defected. The defects in the
first row of sheet piles are more effective onincreasing uplift
pressure and quantity of seepage than the othertwo rows of sheet
piles while defects in the last rows of sheet pilesare the most
effective on increasing the exit hydraulic gradient. 27. Conclusion
This research suggests solutions for preventing expected
weirfoundation failure problems by: Improving the seal between
elements of the sheet piles andrepairing any defects. Sealing any
cracks in the weir foundation by injection of chemicalmaterials or
cement grout. The Same Problem also validated with another FEM
software(Phase2) successfully. 28. Diyala Weir Model in SEEP/W 29.
Seepage Results from SEEP/W
