Stability of a crown wall (superstructure) of a breakwater 1

[geofoun]

We are estimating horizontal and vertical forces due to wave impact on a crown wall which is partly protected by concrete armour units, in order to evaluate the stability of the crown wall, according to CIRIA method (Rock manual, CIRIA special publ. 83/CUR report 154,1991-Jenssen) and we would like your opinion:
a) on the choice of the empirical coefficients a and b for accropode armour units (e.g. a=0.043,b=0.038 for rock armour)
b) on the reduction factor of the horizontal force relative to the shoulder width in front of the wall (if we had x times the shoulder width of the method example)

According to another method (Pedersen 1996) suggested in the Coastal Engineering Manual, the horizontal force results to be about two times the horizontal force estimated by the previous method.

We would also appreciate your suggestion on an alternative calculation method. Please advise.

 

[blueoak]

The Corps CEM is generally considered state of the practice and I never design below it. That said you may want to also use the older Shore Protection Manual 1984?(if you don't have it you have to get it used). The CEM replaced it, but the SPM has easier to use equations. I use it to make sure I did the CEM method right. I believe the SPM can only evaluate a vertical wall since the force calcs for a sloping wall is beyond its scope. I would suggest you put either a slope or curve if possible. A lot of pressure is in the wave collapsing against the wall with an air pocket. The added forms for a curve lets a lot of enegy dissipate as vertical spray if done right. My experience for walls is a max 3 foot waves, otherwise only sloping riprap.