Strength and durability properties of core lithologies from coal-bearing Tyonek formation, Cook Inlet region, Alaska
The Tyonek Formation (late Oligocene to middle Miocene) is a nonmarine unit of sandstone, siltstone, and claystone that contains large quantities of strippable subbituminous coal and lignite. The geotechnical properties, determined by field and laboratory tests on core from the Capps and Chuitna coalfields, dictate the equipment needs for excavation, determination of pit slope angle for mine planning, and durability of excavated spoil to weathering degradation. Point-load strength index tests are rapid and inexpensive field tests approximating the tensile and unconfined compressive strength of rock types. These tests, combined with laboratory uniaxial compression tests, were used to rank the formation lithologies in order of decreasing strength: coal (2670 psi), carbonaceous claystone (835 psi), siltstone (435 psi), claystone (375 psi), and sandstone (145 psi). Except for coal, the lithologies range in hardness from soft soil to soft rock. Laboratory slake durability index tests, which measure the deterioration potential of rock masses as a result of cyclic wetting and drying, were used to rank lithologies in order of decreasing durability: claystone (49%), carbonaceous claystone (46%), siltstone (40%), and sandstone (20%). The cored Tyonek lithologies are noncarbonate, and their strength and durability increase with decreasing grain size and increasing clay-particle content. Compressional wave velocity, combined with point-load data, indicates that most of the rocks could be removed by bull-dozers with ripping blades or by scrapers and shovels. However, coal (with rare exceptions, the strongest lithology tested) would require blasting before removal.
- Research Organization:
- Geological Survey, Denver, CO
- OSTI ID:
- 5950905
- Report Number(s):
- CONF-8505215-
- Journal Information:
- Am. Assoc. Pet. Geol., Bull.; (United States), Vol. 69:4; Conference: AAPG-SEPM-SEG Pacific section meeting, Anchorage, AK, USA, 22 May 1985
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ALASKA
COAL DEPOSITS
LITHOLOGY
GEOLOGIC FORMATIONS
SANDSTONES
SILTSTONES
TERTIARY PERIOD
CENOZOIC ERA
FEDERAL REGION X
GEOLOGIC AGES
GEOLOGIC DEPOSITS
MINERAL RESOURCES
NORTH AMERICA
RESOURCES
ROCKS
SEDIMENTARY ROCKS
USA
011000* - Coal
Lignite
& Peat- Reserves
Geology
& Exploration