INSTRUMENTS FOR DETERMINING THE ELEVATION OF GROUT IN DEEP HOLES,
ARMY ENGINEER WATERWAYS EXPERIMENT STATION VICKSBURG MS
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The need to know the elevation of grout used to seat shock-sensitive instruments in deep holes in connection with underground nuclear testing was responsible for the investigation of devices for determining grout elevation. Four devices were developed and tested in the laboratory and three in deep holes in connection with Project DRIBBLE at Hattiesburg, Miss., and Project CLEARWATER at the Nevada Test Site, Mercury, Nev. Results indicated that 1 a pressure-differential switch is effective where there is an appreciable difference in the density of the grout and drilling mud 2 a coil induction method, utilizing a floating metallic core, is sound in theory and will work provided the drilling mud is not too thick, and there is no leakage of liquid into the hollow metallic capsule 3 a differential transformer will work perfectly where water or thin- to medium-viscosity mud is present in the hole, but its reliability in thick mud has not been established 4 if the density of the grout must approximate that of the mud, a resistivity device, which would detect drilling mud seeded with a metallic powder and pumped just ahead of the grout, should be effective if a suitable metallic powder can be found.
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