8. Design of Coastal Structures
283
Calculation of passive force offered:
Height which offers passive résistance to wall = x.
Rp = 0.5 x ÿ(Kp - Kaj x x2
= 0.5 x (19.5 - 10) x (4.2 - 0.237) x x2
= 18.82 x2
Calculation of tension force in anchor rod:
Anchor rod is placed at 1.5 m from top of the wall. Moment about anchor
level,
Ra(ÿ - 1.5) = Æp((6.8 - 1.5) + 2/3æ), x = 1.18 m
Rp = 26.27 kN/m
Tension in tie rod, T = Ra — Rp
= 65.94 - 26.27 = 39.67 kN/m
« 40 kN/m
Check for overtuming:
Mo = overturning moment caused by forces acting on wall
Mo = moment due to active pressure — moment due to passive pressure
— moment due to water + moment due to surcharge — tension in
tie rod
= 106.83 x 2.27 - 16.27 x 5.92 - 80.06 x 2 + 24.174 x 2.27 - 49.67
= 87.57 kNm
Mr = Resisting moment due to downward forces
= M + W2 + W3
= 0.5 x 6.3 x 25 + 0.5 x 2.8 x 25 + 6.3 x 19.5 x 1.8
= 331.13 kNm
Mr
F = ——- = 1.8 > 1.5. Hence Safe.
Mo
Sliding check:
Active pressures — 0.5 x 0.237 x 19.5 x 6.82 + 30 x 0.237 x 6.8
= 155.197
Maximum possible friction force = pW = 0.6 x 331.13
= 198.678