STABILITY OF AN UNDERGROUND ROOM IN FROZEN GRAVEL

RESEARCH WAS CONDUCTED BY THE BUREAU OF MINES TO AID IN ESTIMATING THE ECONOMIC AND TECHNOLOGICAL FEASIBILITY OF MINING GOLD FROM FROZEN GRAVEL PLACERS IN ALASKA. THIS PRESENTATION DESCRIBES THE PROGRESS OF ONE OF SEVERAL PROJECTS CONDUCTED. AS PART OF THIS STUDY THE SPOKANE MINING RESEARCH CENTER UNDERTOOK TO DETERMINE THE CONDITIONS UNDER WHICH A NOMINAL-SIZE UNDERGROUND ROOM WOULD SAFELY REMAIN OPEN WITH ARTIFICIAL SUPPORTS. THE U. S. ARMY COLD REGIONS RESEARCH AND ENGINEERING LABORATORY HAD PREVIOUSLY EXCAVATED AN ADIT IN SILT PERMAFROST NEAR FAIRBANKS, ALASKA; BUT SINCE WE WERE INTERESTED IN FROZEN GRAVEL DEPOSITS, A 200- FOOT-LONG INCLINED WINZE WAS DRIVEN INTO THE UNDERLYING FROZEN-GRAVEL STRATA, AND A 30- BY 70- BY 8- FOOT-HIGH ROOM WAS EXCAVATED FROM THE RIGHT SIDE OF THE WINZE. THE ROOM AND ADJACENT WINZE WERE INSTRUMENTED WITH 22 CLOSURE POINTS, THREE STRINGS OF SEVEN THERMOCOUPLES EACH, TWO RECORDING THERMOMETERS, TWO PERMANENT SURVEY POINTS, AND SIX HYDRAULIC PROPS. SOME OF THE IN SITU PROPERTIES OF THE FROZEN GRAVEL WERE DETERMINED BY TWO IN-PLACE, MOISTURE-DENSITY TESTS AND 12 NX BOREHOLE PLATE-BEARING TESTS, AND BY DETAILED GEOLOGIC MAPPING OF THE ROOM. AT AN IN-PALCE DRY DENSITY OF 129 PCF AND A MOISTURE CONTENT OF 10 PERCENT, THE IN SITU MODULUS OF DEFORMATION OF FROZEN GRAVEL WAS FOUND TO BE 20,000 PSI AT 23 F. FOR 5 MONTHS, NOVEMBER THROUGH MARCH, AN OPERATING MINE IN FROZEN GRAVEL WOULD REMAIN OPEN WITHOUT ARTIFICAL SUPPORT. FOR YEAR-ROUND MINING--I. E., DURING THE REMAINING 7 MONTHS--THE MINE MUST BE PROTECTED FROM THE HEAT OR ELSE PARTIALLY SUPPORTED WITH YIELDING-TYPE SUPPORTS. IF IT IS SEALED DURING THIS PERIOD, THE MINE BACK WILL CREEP AND A FEW ROOF FALLS WILL OCCUR, BUT THE OPENING WILL REMAIN OPEN WITHOUT ARTIFICAIAL SUPPORT. /AUTHOR/

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Filing Info

  • Accession Number: 00238019
  • Record Type: Publication
  • Report/Paper Numbers: pp 63-64
  • Files: TRIS
  • Created Date: Apr 17 1972 12:00AM