Archive image from page 280 of Deep borehole surveys and problems. Deep borehole surveys and problems deepboreholesurv00hadd Year: 1931 PROBLEMS 269 kept on the dipping surface the point would be displaced, giving two solutions for the strike. C. THREE-BOREHOLE PROBLEMS These are the most favored and oldest of borehole com- putations because they provide a convincing proof and can be applied also to three given altitudes like outcrops at different heights above sea level. Three Boreholes Not in Line First Solution.—If the holes are not put down from a level surface, first reduce the surface
Archive image from page 280 of Deep borehole surveys and problems. Deep borehole surveys and problems deepboreholesurv00hadd Year: 1931 PROBLEMS 269 kept on the dipping surface the point would be displaced, giving two solutions for the strike. C. THREE-BOREHOLE PROBLEMS These are the most favored and oldest of borehole com- putations because they provide a convincing proof and can be applied also to three given altitudes like outcrops at different heights above sea level. Three Boreholes Not in Line First Solution.—If the holes are not put down from a level surface, first reduce the surface level to a given datum such as sea level or that of the lowest borehole mouth. From the survey of the lines connecting A the deepest hole (Fig. 178) to C the shallowest and also from the depth yielded in each hole we Fig- i78. know the plan length of CA which is CiA, also of CB which is EB. We know the respective dips of these lines, , a and j8 since AdBiD is on the horizontal plane, D being where CB produced meets CiBi produced; therefore we also know the plan angles Bi, 6 and 62 between these lines, by construction for di and 62 while d is given. From the two vertical triangles CCiA and CCiD and base triangle ACiD note that tan a sin di tan 18 sin 62 = m and therefore 61 + 2 = 180 - 0 = n n — (52) (53) (54) Substituting m and di in Eq. (52) we get sin {n — 62) m which expands to tan 02 sin 62 sin n m + cos n thus giving 62 for obtaining the strike. (55)
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