Korean anthracite is generally so weak that its compressive strength only ranges from 0.28 MPa to 16 MPa. Furthermore the majority of them. approximately 70 %, reveal a compressive strength and modulus of deformation of less than 5 MPa and 150 MPa respectively. Their bearing capacity is from 0.07 MPa to 0.3 MPa excluding exceptional locations where it attains 5.6 MPa. Accordingly, it is obvious that the technology for developing deep seams should be renovated as early as possible in view. of face support and efficient extraction.
L'anthracite coreen est, en general, tellement fragile que sa resistance à la compression n'est autre que de 0,28 MPa à 16 MPa. Entre autre, la plupart des charbons, approximativement 70 %, revèlent une resistance à la compression et un module d'elasticite inferieurs à 5 MPa et a 150 MPa a 0,3 MPa sauf quelques cas exceptionnels où celle-ci atteint 5.6 MPa. Par consequent, il est evident que la technologie pour developper des couches profondes devrait être amelioree le plus rapidement possible compte tenu du soutènement en taille et de l'abattage efficace.
Koreanische Anthrazit ist gewöhnlich so weich, dass die Druckfestigkeit nur von 0.28 zu 16 MPa erreicht. Ausserdem ergibt sich dieser Anteil ungefahr 70 % der gesamten Kohle, und zwar kleiner als 5 MPa in Druckfestigkeit und 150 MPa in verformungomodul. Die Tragfahigkeit der Kohle tiegt normalesweise zwischen 0.07 und 0.3 MPa, ausnahmsweise bis auf 5.6 MPa. Daher ist eine Weiterentwicklung der Bergbautechnik fur grosse Teufen in Anbetracht des Ausbaus und Ausbansystems erforderlich.
Most of the Korean coal is classified as anthracite. It is used mostly for house heating and partly for power generation and industrial uses. Its chemical composition is fixed carbon(53.7%l, ash(39.5%), H20 (3.6%), volatile matter(3.2%) and sulphur(0.29%).
Coal production in Korea has increased from 5 million tons in 1960 to 22.5 million tons in 1985. Korea retains anthracite reserves of 1.63 billion tons. 90 percent of them was formed during Permaian period of Paleozoic era and the remaining 10 percent from the late Triassic to the early Jurassic period of Mesozoic era.
The coal bearing geologic strata are subjected to the earth crust disturbances in the early Tricassic period, followed by the orogenic action-and strong metamorphism in the late Jurassic period. Korean coal seams therfore are in general very irregular. steep and discontinuous and comprise plenty of folding and faulting structure. The thickness of coal seams fluctuate from 0.6 m to 30 m. The thicker part of the seam occurs typically at the crest and trough of the fold. The predominant dipping of coal seam is from 30 to 90 degrees. The depth of working level at the present time averages 300 m to 400 m, the deepest faces 700 m. Regarding the annual rate of increase in the depth of operational levels, 25 m to 30 m per year, it will be expected to reach 800 m to 900 m from the adit level by the late 19905.
It is therefore urgent to develop deep mining techniques in Korea concerning mechanized coal winning methods and roadway drivage and support systems.
The analysis of coal mine openings requires knowledge of mechanical behaviour of coal. Korean anthracite is extremely soft and friable so that coal specimens can not be machined and the laboratory tests on small coal specimens are not possible. Therefore it becomes important to investigate the accurate strength and deformation characteristics of in-situ coal.
This paper describes briefly the results of - point load test - impact test - plate loading test - borehole jack test for determining the in-situ strength of coal.
With a point load tester (Terrametrics model T-l000), the test was carried out at coal faces of irregular lump coal samples ranging in size from 33 mm to 90 mm.
The range of uniaxial compressive strength(cs) of anthracite was found out to be from 2.6 MPa to 11.2 MPa. The coal with high compressive strength of 28.5 MPa was rarely found at some places. The range of point load strength (Is(50» are shown in table 1. The bedding planes are well developed but cleat planes are less distinct.
For determination of the compressive strength and
(Table in full paper)
strength index(f) of coal of Samtan, protodyakonov's drop hammer test was carried out by using drop hammer apparatus, and compared with the result of plaster cast test. The compressive strength of the coal from Samtan colliery was estimated to be 1.5 to 1.9 MPa and the following formular was obtained from the plaster cast test.
Sc - 0.8' (1 + 2.9 f), MPa (Kim, 1982). This value is approximately same as the value obtained from the plate bearing test.
