274 



DEEP BOREHOLE SURVEYS AND PROBLEMS 



angle CFCi = 8, the full dip of the stratum. The angles 

 ^1 and a also the lengths ACi and CCi are known. 



and 



or 



tan 5 = 



tan 8 = tan a cosec di 



(62) 



Given Three Deviated Boreholes to Determine the Dip 

 and Strike of the Stratum. — Having surveyed three bore- 



FiG. 183. 



holes A, B and C and found their net horizontal displace- 

 ments and depths a line may be drawn in a direction 

 connecting the source and end of each. This line will 

 usually be the shortest line between these points and will 

 have the average deflection of the hole throughout. 



Let us consider a concrete case of three holes set vertically 

 but now deviated until when reduced as above we get their 

 bases data also. Let the surface and borehole data be: 



These points are set out in ABC (Fig. 184), 



