CHAPTER 5,24 CAUSEWAYS AND PIERS For Operation Sandstone a causeway consisting of two rows of steel sheet piling with a soild fill between them had been built between Aomon and Biijiri. This Project required a similar connection between Biijiri and Rojoa to provide vehicular access to the camp on Rojoa, Reports indicated that considerable difficulty had been experienced in closing the final gap in the causeway for Operation Sandstone, and it was anticipated that even greater difficulty would be encountered in the new con struction because of the deeper channel and a probable increase in scouring action due to the existence of the Aomon-Biijiri causeway. Careful study was made at five different points in order to obtain the best alignment and to effect the greatest economy in construction of the Biijiri~Rojoa causeway. Two of these locations had coral heads awash at low tide and were so spaced as to provide convenient pier foundations for 100 foot to 130 foot steel bridge spans. Approximately 600 feet of channel could thus be spanned, with all uncertainties as to pile driving, etc., eliminated, The cost of a steel bridge also compared favorably with the cost of a causeway of the trestle type. (Strictly speaking, a trestle is not a causeway at all, but that nomenclature persisted as the designated name of the structure as built.) Earlier plans for a steel super-structure were abandoned in favor of the relatively low and protected trestle type, comparatively unexposed to damaging action by the proposed experiments. Furthermore, because the location finally adopted was a straight alignment and radial to the zero tower it offered a minimum exposure to possible damage. Prolonged study and field investigation were necessary to determine the penetrating ability and bearing power of wood piles. Here was the prevalent atoll formation consisting of a hard coral cap overlaying softer coral, The thickness of this cap varies and little was known of its ability to grip a driven pile after the cap was once shattered. This called for rigging a pile driver in the field for emplacement of a few test piles to determine whether wood piles could be driven in the desired locations and, if so, what lengths would ba needed for sustaining the required loads, Preliminary tests were successful and designs for piers and causeways based upon driven piles were executed. Thereafter, through the use of standard pile driving equipment, driven piles for causeways, piers, and the like, were employed extensively on the project. In scme cases, directional explosive charges had to be used to pierce the cap coral to permit proper starting. However, for most piles this technique was not required, "With the high degree of teredo and limnoria content in sea water and consequent rapid destruction of untreated wood, especially in the tidal range, it was specified that all wood except the deck lumber be pressure creosoted. Creosote in decking is injurious to many types of cargo and is beneficial only in its prevention of decay. 5-296 Port Orford cedar was