Ch. 34] AIRFIELD SITING AND CONSTRUCTION 649 



or less clay and weathered coral were incorporated. On a clay base, 

 the addition of fill carrying 50 percent or more clay with coral frag- 

 ments was generally unsatisfactory. 



Crushed hard coral proved satisfactory for base course, surfacing, 

 and aggregates. It is easily stabilized with asphalt and bitumen. 

 Large deposits of compact, fine-grained crystalline coral limestone 

 are fully as satisfactory as ordinary limestone for use as riprap or 

 masonry. 



Coral sand, silt, and clay have a tendency toward self-cementing 

 after placing and compaction. This has proved advantageous in air- 

 field and road construction, as the coral rapidly cements itself to a 

 fairly hard surface. 



Massive coral has been effectively used as cyclopean riprap in break- 

 water construction on Guam (personal communication from Allen H. 

 Nicol, U. S. Geological Survey). The "boulders" so used are about 

 10 feet in diameter. 



In the future it is likely that further engineering uses for coral will 

 be developed because of its diverse properties, especially when coral 

 areas have been mapped in detail; for instance, there are commonly 

 "pockets" of hard coral in raised reef strata which generally are soft. 

 Many of these variations have not been fully explained in terms of 

 chemical processes or of ecology. For example, an extremely hard, 

 brecciated, but massive, coral stratum is found in Saipan. 



As would be expected, coral is likely to be cavernous. Furthermore, 

 its contact with the overlying residual clay, while extraordinarily 

 sharp, is also extraordinarily irregular, with pinnacles several feet high 

 extending into the overburden. Because of these characteristics, coral 

 presents problems when used as a foundation. This is especially true 

 when construction changes the established drainage pattern and cavern 

 fill is washed away. Serious cave-ins may result. 



Construction in the sub-Arctic and Arctic involves many as yet un- 

 solved problems for the military engineer. As in the tropics, the 

 strange environment necessitates an entirely new approach to many 

 foundation- and construction-materials problems (see Chapter 14 in 

 this symposium) . 



Airfield Siting and Construction 



The military geologist is concerned with the siting of temporary air- 

 fields mainly. These range from hastily leveled emergency landing 

 strips to extensive installations which, however, are rapidly built from 

 local materials and have an expected useful life of perhaps 5 years. 



The properties of sedimentary materials must be considered in the 



