littoral drift in the area, and on the buildup or erosion of nearby 

 beach areas. 



Other facilities are necessary, in conjunction with, and adjacent 

 to the casting basin, i.e., a carpenters shop and the area where forms 

 for casting units are prepared and serviced; an area where reinforcing 

 steel is stored and preassembled into cages for placing in the forms; 

 a concrete batch plant with adjoining st6rage area for cement, sand and 

 stone aggregate; and other miscellaneous facilities. 



The choice of a site for completing caisson construction after it 

 has been towed out of the casting basin must meet several requirements. 

 Since the units are afloat, waves at the site must be low, with low 

 current velocities, and the units must be protected from extreme winds. 



Water deep enough to accommodate the maximum draft of completed units 

 is required at the outfitting site and along the towing route to the 

 breakwater site. During caisson construction at the outfitting site, 

 drafts and freeboards will change with construction stages. Concrete 

 placement must be scheduled to maintain the unit on an even keel, longi- 

 tudinally and transversely, at all times. 



The outfitting site should be as close as possible to the breakwater 

 site to reduce the time required for towing and setting operations, thus 

 reducing weather hazards. 



b. Bottom Screeding Procedure . Placing the gravel or crushed stone 

 bed and leveling or screeding to proper elevation before setting caisson 

 units will be performed from previously set units. Working from inplace 

 units eliminates the necessity of working from floating equipment with 

 the attendant difficulties and downtime due to rough seas. 



The screeding rig would consist of a gantry, supported at the back 

 end on previously set units and at the forward end by pipe legs and 

 floats. The main truss, which would be free to run from a position above 

 the set units out over the entire area on which the next unit was to be 

 set, would be hung from the gantry. The main truss supports a traveler- 

 carrying stone hopper from which telescopic gravel pipes are suspended 

 to feed the screed box at the bottom. The stone is laid and leveled 

 from the screed box. General arrangements of the screeding rig are 

 shown in Figures 17, 18, and 19. 



To set the first permanent unit, the rig would first be erected on 

 two units temporarily set on the natural bottom without preliminary bottom 

 preparation. The selection of such a suitable area adjacent to the main 

 breakwater site, is an important requirement in planning the site location. 



With the gantry run fully forward, the rig would extend from the 

 previously set units over the 246-foot length of the next unit to be 

 placed, and be supported on the legs and floats beyond. The system of 

 legs and floats provides a buoyant force at the forward end of the gantry 



33 



