CHAPTER XI 



PROBLEMS 



In this chapter we purpose deahng with those problems 

 useful in prospecting and location work generally as are 

 provided by a study of the data afforded by borehole devia- 

 tion instruments, core evidences and photographs of bore- 

 hole walls. 



A. ONE-BOREHOLE PROBLEMS 



To Obtain the Penetration Point of a Borehole and a 

 Stratum. — Of the several mathematical methods of dealing 



Fig. 164. — Borehole dipping with the beds. 



with this problem few are suited to meet the needs of bore- 

 hole conditions, because the data usually assumed are 

 frequently the least accessible. The best method for our 

 purpose is the conditional formula method. Let the bore- 

 hole BBi (Fig. 164, here shown dipping with the stratum 

 but steeper than the beds) have a dip a and the stratum 

 8. It meets the stratum at C at a height h above a horizon- 

 tal plane laid through any point A in the stratum, e.g., 

 a point known in a mine, on an outcrop or located otherwise. 

 Point A need not be accessible if we know the dip of the 

 stratum 8. If B' is the vertical projection of B, the bore- 



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