42 



DEEP BOREHOLE SURVEYS AND PROBLEMS 



It is preferably, but not necessarily, suspended from the 

 pulley S over the hole center C at the surface. The dis- 

 tance CB varies in amount and bearing according to the 

 deflection. If this suspension point >S is at a height h 

 above, and the basket A at a depth D below, the surface 

 and the measurable distance CB be called 

 m, then the deviation X of the hole is 

 obviously 



D + h 



iii}ii/nni/ii/i/i/ 



X ■= m -\r X 



m 



h 



(2) 



Fig. 20. — The lantern 

 basket method. 



Erlinghagen^ simplified the process in 

 a survey of freezing shaft boreholes for 

 the shaft sinking firm of Gebhardt- 

 Nordhausen. He employed a drum of 

 0.314 m. diameter, i.e., 1 m. circumfer- 

 ence, which carried a wound copper wire 

 exactly 10 m. above the center of the 

 mouth of the hole. It carried a heavy 

 weight or plumb bob which moved freely, 

 allowing the wire to take up an exact perpendicular posi- 

 tion. A crosspiece with two measuring lines at right angles 

 is fixed on the hole mouth to facilitate reading. The depth 

 is taken from the number of unwound coils from the drum, 

 each being 1 m. The computation (2) above now becomes 

 ^ ( D + 10 \ 



The method is not bound to fail when the wire fouls the 

 sides of the hole, for in case of the hole deviating back to its 

 original position at greater depths the wire will hang free 

 of the sides. The method can be applied for depths down 

 to about 300 ft., and instances of its successful application 

 at over 600 ft. are on record. Certainly with big deflec- 

 tions it is useless, but for surface and near-by subsurface 

 conditions in most holes down to 100 yd. it is a useful 

 auxiliary record. 



The all important dimension m is checked as follows 

 (Fig. 1, Plate II). The coordinates {xiy-^ of C, the center 



1 Gluckauf, No. 23, 1907. 



