Ch. 34] SUMMARY 653 



The stability of loose materials must also be considered (see Chapter 

 11 in this symposium). The ideal situation is the presence of nearly 

 horizontal strata of constant thickness, although, in excavating into a 

 back slope, a slight dip toward the tunnel entrance will facilitate 

 haulage. In order to prevent cave-ins, thorough drainage must be in- 

 sured and dipping strata carefully examined for intercalated clay lay- 

 ers and weathered zones that may serve as slip planes. The stability 

 of unconsolidated or semi-consolidated materials generally decreases 

 with advanced rounding of their constituent grains. Stability of such 

 materials can be increased by injecting fluid quick-setting cement 

 (sodium or potassium silicate). This, however, is not often possible 

 under military operational conditions. 



By contrast, the recently developed interest in permanent under- 

 ground installations is expressed in terms of factory-sized caves or 

 excavations. It is the consensus that natural caves are useless for 

 this purpose because of the torrential floods that are likely to occur in 

 them. The problem that faces the engineer and the geologist is, there- 

 fore, the planning of excavations on a very large scale; it must be ap- 

 proached with the point of view of the civil engineer rather than with 

 the "expedient" approach demanded of those involved in military con- 

 struction. 



Other Applications 



The usefulness of metallic-mine detectors is sharply limited by the 

 presence of such minerals as magnetite in beach sands. Field tests 

 proved this on the Sagami Bay beaches, selected for landings in the 

 invasion plan for the Tokyo Plain. The presence of such sands can 

 be predicted by identification of their source terrane. 



A subject that demands further study is the effect of shell fire on 

 rock, with especial regard to its splintering qualities. Defining this 

 with any degree of accuracy is a complicated process; it depends on, 

 among other factors, whether the rock is fractured, massive, or strati- 

 fied, wet or dry, the degree of weathering, and the amount of vegetation 

 overlying it. The caliber and type of projectile must, of course, be 

 considered, with especial regard to its penetrating power. 



SUMMARY 



The geologist can contribute to military intelligence and operations 

 by his ability to predict ground conditions and the location, type, and 

 amount of ground water and of useful earth materials. Cross-country 

 movement and construction of underground installations and airfields 



