646 whitmore. MILITARY GEOLOGY [Ch. 34 



tion of the more obvious supply. Criteria and methods of the civilian 

 water-supply geologist and hydraulic engineer are generally applicable 

 except that, in supplying troops in the field, it is more expedient to 

 develop easily reached supplies of small yield than to drill deeper for 

 more adequate supply (U. S. War Department, 1945). 



Construction Materials 



Sand and gravel for concrete aggregate, fill, and base course are 

 the earth materials most in demand for rapid military construction. 

 Clay, for mixing with coarser material as binder, is needed. Crushed 

 rock must be procured for road metal and ballast. To a lesser extent, 

 rock must be quarried for riprap and for rough-cut dimension stone to 

 be used in hasty fortifications or other structures. 



The properties required for these uses are discussed in Chapters 8 

 and 24 of this symposium; the peculiarly military problems in regard 

 to geologic construction materials are (1) locating them in advance 

 of operations, generally by means of aerial photographs, and (2) 

 utilizing substitute materials when circumstances prevent use of those 

 normally specified for a given purpose. 



In developing rock material for engineering use, either civil or 

 military, the following major factors must be considered: accessibility, 

 overburden, volume, and geologic structure. When considered in the 

 light of purely military operations, however, the relative emphasis ac- 

 corded these factors may vary greatly. The accessibility factor may 

 be taken as an example. Normal military usage requires development 

 of construction materials sources within 5 miles of the project site, but, 

 when necessary, as in the Leyte operation, hauls may be resorted to 

 that result in as much as a 5-hour round trip per truck per load; 

 unheard of, of course, in civil-engineering practice. 



Military structures built under operational conditions are not ex- 

 pected to last long. Materials requirements are not, therefore, so 

 rigorous as in civil engineering. Within the resulting wider range of 

 acceptability, choice of materials is likely to be governed mainly by 

 the equipment available. Consider, as an example, development of 

 concrete aggregate by a construction battalion operating in a large val- 

 ley. If a dragline is available, stream gravels will probably be used; 

 if bulldozers are at hand, a stripping operation may be begun on a 

 gravel terrace. 



In the search for sand and gravel, river banks, bars, terraces, and 

 flood plains have long been the mainstay of the military engineer. The 

 less obvious sources, such as abandoned stream channels, glacial- 

 outwash deposits, and eskers, being recognizable in aerial photographs, 



