ENGINEERING STRUCTURES 151 



Conclusions The main conclusions to be drawn from the 

 investigations are that while, on the assumption of simple 

 hydrostatic transmission of pressure, the effective internal 

 pressure due to wave impact cannot exceed that exerted by 

 wave impact on the sea face of a breakwater, the pressures 

 produced, if the energy of the wave is devoted to compression 

 of air in the open joints, may amount to approximately twice 

 this magnitude. If, however, conditions are favourable to 

 the production of water-hammer, considerably greater 

 pressures, up to some fifteen times the face pressure with very 

 high velocities of impact, are to be regarded as possible. 



The results suggest the desirability of providing a free 

 outlet for such water as may percolate to the interior of a sea- 

 wall or breakwater, by means of a series of weep holes or drains 

 opening on its sheltered face. Such drains, preventing the 

 accumulation of internal water, would be an effective guard 

 against the production of internal pressures of sufficient 

 magnitude to affect the stability of the structure, whether due 

 to water-hammer or to air compression. 



ARNOLD HARTLEY GIBSON 

 WILLIAM NELSON ELGOOD 



