Two moderately severe storms occurred during January 1958. Although 

 the island was in an incompleted and vulnerable state, it received light 

 damage. The contractor's loading-out pier was damaged in the second of 

 these storms and required a month for repairs. 



The 68 steel conductor pipes were driven when the core elevation was 

 at about +11 feet. These pipes, the initial casing for future oil wells 

 to be drilled through the island by the owner, were driven 15 feet into 

 the original ocean floor. Work on the concrete walls on the surface of 

 the island was started after all the conductor pipes were driven. For 

 this work a small concrete batch plant was placed on the island. Work was 

 substantially completed in August 1958. 



h. Field Engineering - One basic problem for the engineer providing 

 supervision and inspection throughout the construction was to ensure that 

 the filter zones of the revetment construction were adequately placed and 

 that no openings in this essential element of the island's defense were 

 left for the relentless attack of the seas. Another responsibility was to 

 see that the various rock layers were placed within acceptable location 

 tolerances. The fact that two-thirds of the island's cost was for materials 

 placed below water points up the difficulty of these problems. Survey and 

 layout work was basically a contractor responsibility, and a high percent- 

 age of his marine work was directly or indirectly concerned with performing 

 this task. A lead line was almost constantly in use during all underwater 

 material placement operations. 



The magnitude of the survey work made it impractical for the engineer's 

 staff to check all survey operations. Field inspectors observed and spot- 

 checked the contractor's marine survey operations, but considerable 

 reliance was placed on independent surveys by a modem ultrasonic depth 

 recorder of the underwater mounds placed in the early stages. An essential 

 feature of this instrument was the narrow (approximately 6°) cone of res- 

 ponse, which allowed adequate delineation of the sharp breaks in grade 

 typical of the island form. As anticipated, vertical accuracy of the 

 instrument when properly calibrated by a steel plate suspended by a survey 

 tape was not a significant problem. 



The echo sounder is a portable instrument, so the transducer was 

 mounted outboard toward the stem. A preferred method of position control 

 was by taking simultaneous sextant angles on three targets from the boat. 

 To help reduce plotting errors, a platform was rigged to overhang the 

 transducer, so that both sextants could be located over the transducer when 

 taking position shots. To help obtain conveniently large horizontal chart 

 scale, a special high-speed chart drive motor was installed in the echo 

 sounder. In addition, "spoiler plates" were lowered into the water direct- 

 ly behind each of the twin propellers. The spoiler plates effectively 

 reduced boat speed while maintaining good rudder control. The slow boat 

 speed was desirable for close spacing of position shots and to aid in main- 

 taining a large horizontal scale on the echo sounder charts. These tech- 

 niques enabled a small field staff to take accurate and continuous three- 

 dimensional sweeps of underwater construction when required. 



17 



