the fill at each joint using a special sacrificial driving tip that forces the tip to follow the 

 joint. Grout is then forced through the pipe as the pipe is withdrawn. If the gap is so wide 

 the grout escapes through it, a special rubber or plastic tube must first be inserted in the 

 pipe to act as a form to retain the grout after the pipe is withdrawn. 



(4) ShoaUng of channels and basins may present a difficult maintenance-dredging 

 problem. Ordinary excavating equipment such as draglines, clamshell-dredges and the usual 

 hydraulic dredges cannot safely work near armored slopes, vertical walls, fixed piers, and 

 docks or under piers and docks whether they are fixed or floating. A new type of dredging 

 suction head will now solve this problem. It uses high-pressure water jets to loosen the 

 bottom material and compresses air to operate pneumatic slurry pumps in the suction head 

 which force the material in high concentration mixture with water through the discharge 

 Une. The suction head has no moving parts and is operated entirely through flexible tubing 

 leading down to the suction head from a floating or landside water pump and air 

 compressor. Thus, it can be more easily guided into areas that would normally be difficult 

 to reach without endangering either the suction head or nearby structures. It is only 

 necessary to guide the suction head at constant depth to all parts of the shoaled area to 

 restore the desired uniform depth of the basin or channel. 



(5) Fixed piers and other structures built on piling need the same maintenance as 

 landside structures except that in a moist air environment they may require more frequent 

 painting and rust-prevention treatment. Moreover, the supporting piles and bracing members 

 must be examined periodically for evidence of deterioration. Damaged or badly deteriojated 

 piles may have to be removed and replaced occasionally, and bracing members should be 

 replaced when broken or otherwise cease to be functional. 



(6) Floating piers and docks may deteriorate in several ways: (a) loss of flotation, 



(b) working of bolts against wooden side stringers or connections of finger to headwalks, 



(c) loosening of hinged connections, (d) fatigue failure of structural members or their 

 connectors due to continuous flexing under wave action, and (e) abrasion of deck surfacing. 



The most troublesome problem is usually flotation loss, which may be partial for foam 

 floats but sometimes total in hollow-shell floats. A periodic check of the freeboard in 

 various components of the floating system will indicate where flotation loss has occurred. 

 Nonleaking hollow floats sometimes take on water by internal condensation of airborne 

 moisture or possibly by infiltration of surface water through breather caps and only need to 

 be pumped out occasionally. Some foams are partially water-absorbent and may stabilize at 

 a satisfactory level after becoming saturated over a period of time due to capillary intrusion. 



In seawater, an incrustation of marine growth may cause some loss of flotation, although 

 most plant and animal life have the same density as its water environment. The shells of 

 crustaceans cause most of the settlement due to marine growth, and have to be scraped 

 periodically to hold the desired freeboard. In some marinas, scuba divers may be hired to 

 clean the hulls of boats and bottoms of flotation units supporting floating piers and docks 



246 



