. Deep borehole surveys and problems. Boring. 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 â = m -\r X m h (2) Fig. 20.âThe lantern basket method. Erlinghagen^ simplified the process in a survey of freez
. Deep borehole surveys and problems. Boring. 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 â = m -\r X m h (2) Fig. 20.âThe 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 m. diameter, , 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, Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may
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