ENGINEERING STRUCTURES 



135 



suitable for the production of such pressures it is probably 

 safe to say that in a sea-wall the maximum internal pressure 

 due to air compression never exceeds twice the face pressure, 



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=?<; 



-I 



X~Y 



FIG. 1 



i.e. does not exceed some 5 - 75 tons per square foot with a 

 velocity corresponding to a head of 100 feet. 



Where the crevice opens into a cavity of any considerable 

 size in the interior of the-sea wall, or where, as will be usually 



