The last tvro illustrations relate to bulkhead construction. Figure 9a 

 shows a section through a conventional bulkhead. The steel wale is located 

 for erection convenience on the outside of the sheet piles above meai low 

 water. A steel cap channel is used in forming the top curb. The steel 

 wale is severely exposed and deteriorates rapidly. The channel cap shares 

 a fate onl}'- sli5:htly less severe. The tie-rod corrodes badly adjacent to 

 the bulkhead. By the sim-^le procedure of transferring the wale to the 

 inside face of the sheet piles and protecting the upper channel virith con- 

 concrete as shovm in Figure 9b, the life expectancy of the v/ale is greatly 

 increased. Critical corrosion of the tie-rods can be prevented by paint- 

 ing and VvTap-oing the 6 ft. length of rod adjacent to the sheet niles, or 

 encasing it in concrete. A concrete cap and curb built along the top of 

 the sheet piles is far superior to the conventional channel curb. Besides^ 

 it acts as a much better distributing beam for the bulkhead system. At 

 locations v/here corrosion is known to be severe, encasement of the upper 

 portion of the piling in a concrete envelope, as shovm in Figure 9c, is 

 necessary. A saving in vreight of steel can be made by varyin:; the length 

 of alternate pairs of sheet piles, as shown in Figure 9d. 



Figiure 10 illustrates a bulkhead design vfhich is adaptable to repair at 

 a later date, after having served an initial normal life. In this case, 

 the sheet piles are anchored at tvjo levels because of the high backfill 

 elevation. The lower wale is located on the outer face of the piling, 

 but is about me foot below mean low water to reduce tide zone exposure. 

 At the "zone of failure" shoYm, the deteriorated areas of the sheet piles 

 permit leaching and escape of backfill material v/hich causes a lowering 

 of the top grade. This type of failure does not endanger the stability 

 of the biilkhead as a whole, because the loiver wale and tie-rod system 

 remain intact and retain the original alignment of the lower portion of 

 the sheet piles. The upper ,:.ortion of the bulkhead can be repaired as 

 shown in Figure 10b. A narrow relieving platform is built behind the 

 sheet piles to reduce the lateral pressures and a concrete gravity retain- 

 ing well is constructed above the platform. ^ bulkhead, reconstructed in 

 this manner, '..'ill generally last longer than the original construction, 



RecomiTiended Design Practices: 



The more important lessons learned from experience on the deterioration 

 of timber, concrete and steel waterfront structures may be summarized as 

 follows: 



a. Since maximum deterioration occurs in the tide zone the number of 

 structural members located therein should be kept to a practical 

 minimum. The elimination of bracing v/ithin the tide range is the 

 first step tovrard a better design. 



b. Round members because of their smaller area and better flovi character- 

 istics for wave action generally have a longer life than other shapes. 



G - lit 



