8. Design of Coastal Structures
289
Calculating the active earth pressure
Pa (at point A) = (7™ x Hw) = 10.25 x 7.5 = 76.875 kN/m2
Pa (at point B) = 0
To find a
Pa (@ AA') = y'(Kp - Ka) x a
76.875 = 9.75 x (1.625 - 0.307) x a
a = 5.98 m
Calculating the passive earth pressure
Pp (at point C) = ^'(Kp — Ka) x dl — 12.85dl kN/m2
By solving active and passive pressure we get
dl = 8.6 m
D - dl + a = 8.6 + 5.98 « 14.5 m
Increase it by 20% - 40% — provide depth 19 m
But the case we hâve taken is practically not possible, so provide
depth 12 m.
Section modulus Z' = 320301.84 cm3
Based on ail the three cases the most critical case is the Case 3.
Problem XI
A cantilever sheet pile wall penetrating a granular soil is shown in the figure
below. Here, Li = 2m, L2 = 3m, 7^ — 15.9 kN/m3, 7sa/ = 19.33 kN/m3
and 0' = 32°.
(a) What is the theoretical depth of embedment, D?
(b) For a 30% increase in D, what should be the total length of the sheet
piles?
(c) What should be in the minimum section modulus of the sheet piles?
Use aau = 172 MN/m2.