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Malaysia Water Research Journal
The factor of safety sliding may be expressed by Eq. [2] below, which
generally a minimum factor of safety of 1.5 is required:
where,
ΣR V
= sum of the vertical resisting forces
ΣR H
= sum of the horizontal resisting forces
δ = angle of friction between the soil and base slabk = the range between 1/3
to 2/3
c = cohesion of soilR = resistance force B = bottom length of structure
Table 1. Overturning check on coastal block structure at point 0
Option Ɵ Moment at 0 Remark
ΣM+ (kNm)
ΣM- (kNm)
1 300 58.2 18.88 3.1 Ok
2 450 18.1 7.58 2.4 Ok
3 600 8.74 7.64 1.14 No (redesign
3a)
3a 600 14.71 7.64 1.9 Ok
Table 2. Sliding check on coastal block structure at point 0
Angle (°) ΣR V
(kN) ΣR H
(kN) B (m) FS Remark
30 68 18.45 1.85 3.7 Ok
45 40.2 15.36 1.2 2.8 Ok
60 31.75 12.34 1.05 2. Ok
The result of analysis is given as above. Table 1 showed the moment acting
on coastal block for stability analysis on overturning check. The factor of safety
for overturning is more than 1.5. The force acting on coastal block for stability
analysis on sliding check are summarised as shown in Table 2. The stability of
coastal block is analysed using full scale data collected from site and secondary
data where necessary.
The structure is exposed to both forces from the wave action and lateral
earth action specifically active earth pressure. As the block moves away from
the backfill, there is a decrease in the pressure on the wall. The decrease
continues until a minimum value is reach after which there is no reduction in the
pressure and the value will become constant. Coastal block must be designed
to withhold wave actions in order to maintain its stability against overturning and
Institut Penyelidikan Hidraulik Kebangsaan Malaysia (NAHRIM)
99
National Hydraulic Institute of Malaysia (NAHRIM)