141 CHAPTER II, SECTION 4 MAN-MADE ISLANDS AND CAUSEWAYS MAN-MADE ISLANDSI, I, & III. In order to locate certain DOD scientific stations at the proper distance from Station 18, the construction of three islands in the Dog-Charlie reef was required. Two of these islands were 220'x 140’, one was 90’x 140’, and all three were built to elevation 9.5 from approximate reef elevation of 1.0. Bulkheads were formed of 60-pound rail piles which were backed by 3inch timbers. The area was then backfilled with available reef coral and sand. The rail piles, driven 8 feet into the coral on 5-foot centers, projected approximately 9 feet above the reef. These rails were interconnected on the outside by two horizontal rails which acted as walers. The walers were connected to the piles by Ubolts, while the horizontal 3-inch timbers were fastened to the inside of the rails by J-bolts. Opposite bulkheads were connected by 1-\inch tie rods for distribution of the load. The bulkheads which faced the shot site, being subjected to reflected pressures, had the tops curved back to prevent disturbance of the shock wave. This was accomplished by splicing curved 6-inch steel channels to the rails at a point about four feet from the top of the rails, and by fastening the timbers to the curved channels. Figure 2-149. OFFSHORE YVONNE. Construction of an island and two causeways at Yvonne was required in order to properly locate Stations 24 and 1819 in relation to other stations, to reduce the possibility of fall-out and damage to other structures from the LaCrosse event (Station 24), and to properly locate the Station 1524 pipeline. As finally built, the island was 110’ x 100’ with a T-shaped addition approximately 90 feet on one side, 40 feet on the other, and 40 feet wide. This island was connected to Yvonne by a causeway 470’ long and 24’ wide. The causeway that was provided for the Station 1524 pipe array was 1500’ long and 40’ wide. The islands and causeways were built to a plus 9.0-foot elevation. The design was standard for this type of work as discussed in this report under the sub-heading of Man-Made Islands I, II, and III. Rails at this site were driven into T-shaped holes which were drilled into the coral because of its hardness. A change in requirements after construction had started necessitated removing and redriving a numberof piles in order to increase the size of the island. Man-Made Island No. 1-10% Complete Page 2-171