corrosion is left undisturbed the piling may last 35 years or longer. 

 If stone is used to fill the structure ^ its life will be greater than 

 with sand filling, as the holes which first corrode through the web will 

 have to be of considerable size before the stone will leach out and re- 

 duce the stability of the s tructure , 



382= iiZi^l_S£E£2,» " '^^it) structures are constructed of timber in 

 compartments,, some of w^hich are floored, The cribs are floated into 

 position and settled upon a prepared foundation by filling the floored 

 compartments with stone. The unfloored com.partments are then filled 

 with stone for stability. The structure then is capped with timber^ 

 concrete,,, or capstones. The superstructure and decking of cribs set 

 on a rubble -mound foundation are often of timber to allow for settlement 

 of the crib. >Jhen decay of the timber requires replacement, concrete 

 may be usedj, as the crib will probably have settled into permanent position 

 by that time» 



383= Timber crib structures are suitable for depths of $0 feet or 

 more. The foundation is prepared in a mamier similar to that for con- 

 crete caissons. Tim.ber structures are not suitable in salt water where 

 marine borers are present. However^, in fresh water timber continually 

 submerged or saturated does not decay and the structure will last many 

 years. Kxaj.aples of timber crib breakwaters are shown in Figure 125 and 

 126, 



38i|. , Solid Fill, - A solid fill structure is som.etimes constructed 

 where it is desired to prevent wave action passing through the structure. 

 One comiion type of solid fill breakwater consists of hydraulically 

 deposited sand fill between stone mounds^, with an armcr of heavy rubble- 

 "tone on the seaward side to protect the smaller material in the stone 

 mounds against wave action. An example of solid fill breakwater is 

 shovm in Figure 127, 



38!; < ,-,iphglt ic Materials . - In som.e instances the core and capstone 

 have been consolidated to various depths by forcing hot asphaltic con- 

 crete into the interstices between the atones = Typical sections of 

 structures xAere asphaltic concrete has been used are shown on Figure 

 128, Although the asphaltic concrete appears to serve its purpose in 

 the cases shown^ adjacent sections indicate that the use of portland 

 cement concrete would probably have been superior. Asphaltic concrete 

 used at other locations such as the Colujr.bia River and Los Angeles Harbor 

 has proven ineffective, 



386, Selection of Type , - The selection of the type of offshore 

 breakvjater is dependent on many factors, I^rincipal factors which may 

 affect the selection of type include natural forces to be resisted,;, 

 foundations^ availability of material^;, desired life, and. cost. Probably 

 all are reflected in the cost. The desired life is also a function of 

 the use of the structure. 



