the middle jetty along the littoral zone and 16,000 cubic yards had passed 

 through the north jetty in spite of placement of the sealing stone. 

 Consequently both jetties had to be sealed by such means as would produce 

 a permanent and completely impervious barrier. 



DEVELOPMENT OF THE PLAN FOR SEALING 



Figure 2 shows a typical cross section of the jetties. They are 

 16 feet wide at the crest, at an elevation of lU feet above mean lower 

 low water, with side slopes 1 vertical on 1.5 horizontal extending to 

 the ocean bottom on both sides. The armor, composed of stone weighing 

 1 to l£ tons each, is lH feet thick over the top of the core and about 

 10 feet thick over the sides of the core. The void ratio of the armor 

 is generally about 33> percent, but the size of individual voids range 

 from a fraction of a cubic foot to several cubic feet. The voids are 

 staggered, and only in exceptional cases would any system of voids 

 provide a continuous corridor between any surface and the core, which was 

 not constricted in many places to openings of only a few square inches. 

 Thus, the prevailing structural characteristics of the jetty precluded 

 all attempts to intrude, by action of gravity, any but the most fluid of 

 substances. At the same time, head differentials and dynamic thrusting 

 of impinging waves constantly caused water to surge back and forth 

 throughout the armor section with considerable velocity. 



No materials were found which could be combined in any way to 

 provide the fluidity required for intrusion through existing voids and 

 still resist erosion of water in motion during the period of solidifica- 

 tion. It was, therefore, decided to explore the possibility of drilling 

 vertical intrusion holes lU feet deep from the top of the jetty to the 

 core, through which grout could be introduced through an inserted nozzle. 

 As the drill used for this purpose would have to drop through voids and 

 encounter wiggling and sloping surfaces, the success of rotary drilling 

 was in doubt. Contractors familiar with the use of percussion drills 

 generally indicated their belief that the holes could be made with a 

 wagon drill. 



MATERIALS 



Grout . - After a short investigation of the properties of asphalt 

 mixtures, cement-sand grout with such admixtures as might be found to 

 produce the required characteristics was settled upon as the most practi- 

 cal sealing material. The grout would need to be repellent to water and 

 cohesive, with as little internal friction as possible; it would have to 

 migrate freely at low pressures with no tendency to pack, as no pressure 

 other than gravity head could be maintained; and it should pass freely 

 through short runs of pipe or hose less than 2 inches in diameter at 

 pressures below 200 p.s.i. in order that the rate of intrusion through 

 a small hole should be as great as possible. It was reasoned that large 

 masses of grout placed in short periods of time would suffer the minimum 

 erosion by surging water. 



