PROBLEMS 



261 



true dip of the seam 5 is shown by the angle A^DiAi and its 

 dip a in the direction of the borehole by the angle A2BA1. 

 WXYZ is the horizontal reference plane 



/3 = A2BA = dip of borehole, and by the funda- 

 mental dip formula for an apparent dip a and 

 true dip 8 

 tan a = tan 8 cos 6. 



t = the true thickness of the beds. 



Fig. 174. 



The true length of the borehole AB and its direction are 

 found from the core and the survey. 



t = AAi cos 5 



A2B.A2A1 



= {AA2 — AoAi) cos 8 



AB sin 13 — 



A2B 



cos 5 



(45) 



= {AB sin ^ — A2B tan a) cos 8 



= {AB sin i3 — A2B tan 5 cos d) cos 8 



= AB{siia. jS cos 8 — cos /S sin 8 cos d) 



III. Boreholes to Particular Points 

 These may be grouped into two suites : 



1. Those set at a definite angle, the problem being to 

 find where it will hit a known seam, lode, workings, etc. 



