INSTRUMENTS FOR DETERMINING THE ELEVATION OF GROUT IN DEEP HOLES. REPORT 2. FURTHER INVESTIGATIONS,
ARMY ENGINEER WATERWAYS EXPERIMENT STATION VICKSBURG MS
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A special grout designed to match the strength, density, and sonic characteristics of the surrounding medium is required for seating shock-sensitive instrumentation in drilled holes in connection with underground nuclear tests. To ascertain that grout has actually surrounded the instruments, three methods of detecting the arrival of grout at any predetermined elevation in the hole were developed. Two of the methods utilize the difference in density between the drilling mud or water initially in the hole and the displacing grout. The third method utilizes a metallic-seeded mud that is pumped downhole immediately ahead of the grout. This report covers tests to determine the reliability of the methods. The pressure differential switch is the most reliable device and will operate when there is a minimum difference in density between the drill mud and grout of 5 pcf. The differential transformer densimeters will only operate reliably when the difference is 25 pcf. The resistivity method performed satisfactorily in laboratory tests however, all ferromagnetic, highly conductive metal and ceramic powders tested oxidized after a short time in water and thereby lost their ability as conductors. Special techniques for calibrating the switches and densimeters and for protecting them during lowering operations are given. As a result of the investigation, use of the pressure switch is recommended. should pressure switches not be available, the transformer densimeter can be used if there is a minimum difference in density of 25 pcf.
- Miscellaneous Materials
- Test Facilities, Equipment and Methods