Proceedings of the Polytechnic Association. 971 



'On a liberal scale, with allowances for various contingencies. Its 

 plan sliould also be so devised as to reduce accidental contingencies 

 to the lowest possible number, while it secures permanent construction. 



With this view I have estimated for the use of a solid stone founda- 

 tion for the entire structure, on each side, formed of a rip rap wall, 

 easily and cheaply made, by dumping refuse Palisade stone, which 

 involves no serious trouble in building, and cannot be displaced when 

 completed, nor can it settle, 



Tliis work, except at the tunnel center, will form the foundations 

 of the guard locks, as well as the sea wall ; at the tunnel center, for 

 convenience of adjustment and grading, a continuous pile foundation 

 is estimated, cut off at a uniform level, near ordinary river bottom. 



On these foundations, of which the piling will precede the rip rap 

 fill, the guard locks will be built, as now estimated, in five timber 

 and plank caissons, carefully bridged and braced, with knees and 

 other frame supports, the center caisson, 258 feet by seventy, being 

 sixty-five feet deep, to carry the tunnel division on both locks for a 

 continuous length of 250 feet, and the central part of both locks. 

 This being properly sunk on its piled bed and anchored, the rip 

 rap base will be made on each side, to a level of thirty feet below low 

 tide, and on this four caissons, each 201 feet by 118, and forty feet 

 deep, will be anchored and sunk, providing for the ends of each lock, 

 joining the center part by cutting through the caissons ; a simple 

 device, the main work being performed, will provide for the return 

 walls or each lock face. 



This being done, the rip rap work will be built on the ITew York 

 side, to its proper level, fifteen feet below low tide, and on the north 

 or south side, the crib work will be built and sunk as planned, and the 

 sea wall carried up from low tide to its coping level. The opposite 

 crib work and sea wall can then be made in smooth water, and the 

 central filling of earthwork completed in advance of, and connection 

 with, the tunnel work from the lock tunnel to the shore. 



All this being done, under conditions of no extraordinary difficulty, 

 and the guard locks ready for use, the rip rap walls on the Brook- 

 lyn side can then be brought up to crib base, on one side of the pier, 

 and to mean high tide on the other side, keeping the face a little 

 slack on its line. This done, the opposite crib work can be anchored 

 and sunk, and its sea wall completed, and afterward the rip rap dam 

 can be dressed over on its slope to crib base, and that side completed 

 in still water. As the object to be accomplished by this temporary 

 rip rap dam is simply to control, without fully shutting off the tidal 



