1、翻译部分Effect of size on the compressive strength of coalH. MoomivandFaculty of Engineering, University of Urmia, IranABSTRACT: The compressive strength of coal depends on the distribution, type and condition of discontinuities. In the smaller specimen, the probability of finding larger discontinuities
2、 is smaller and the compressive strength is thus higher. All groups of laboratory and in situ test results were analyzed by a DataFit computer program separately. It was shown that the effect of size on the compressive strength of 10 different groups of coal is not the same. Compressive strength of
3、different groups of coal specimens had a high scatter for the same size and strength-size relationship bad high deviation when all groups of results were mixed. Compressive strength of specimens was divided by the compressive strength of a specimen having a size equal to d (in this analysis 50.8 mm)
4、 in any group of test results. Consequently the dimension of strength in all series of tests was omitted and the relationship between the ratio of compressive strengths and size for all groups of results was determined. From extrapolating laboratory and in situ test results, the relationship between
5、 compressive strength and size of all cubic coal specimens was derived.1 INTRODUCTIONThe discontinuities of various sizes are present in rock mass. The compressive strength, as a function of discontinuities, increases with a decrease in size of rock specimens, A new definition for size effect on the
6、 compressive strength has been given as it can represent the phenomenon. Most of the experimental results available are for coal and are concerned especially with the compressive strength of cubes of various edge dimensions. The effect of size on the compressive strength of coal has been investigate
7、d by conducting tests both in the laboratory and in situ. The effect of size on the compressive strength of all laboratory and in situ test results of cubic coal specimens has been analysed using DataFit computer program (1992). From extrapolating laboratory and in situ test results, the relationshi
8、p between compressive strength and size of all cubic coal specimens has been derived.2 EFFECT OF SIZE ON THE COMPRESSIVE STRENGTH OF COAL SPECIMENS2.1 Laboratory testsCoal contains various discontinuities such as cracks, pores, etc. The compressive strength of rock (coal) depends on the distribution
9、, type and condition of discontinuities. In the smaller specimen, the probability of finding larger discontinuities is smaller and the compressive strength is thus higher. The effect of size on the compressive strength of different types of rock specimens is not the same (Moomivand, 1993).The compre
10、ssive strength increases with a decrease in size of coal specimens (Daniels & Moore 1907, Rice 1929, Lawall & Holland 1937, Steart 1954, Gaddy 1956, Evans et al. 1961), Gaddy (1956) tested the compressive strength of a large number of cubes from 5 different seams including Pittsburgh, Ctintwood, Poc
11、ahontas No.4, Harlan and Marker having edge dimension from 0.051m to 1.626m and he proposed the following relationship between compressive strength and specimen size: c1=KD-0.5 (1)wherec1 = compressive strength of cubical coal specimen having edge dimension D; and K = a coefficient depending upon th
12、e chemical and physical properties of the coal.2.2 In situ testsIn the. cutting and curing of a rock specimen for laboratory testing, not only are cracks, joints and weaknesses reduced from a large size (rock mass) to a small laboratory size but also with the transporting of specimens from mines to
13、the laboratory and with the cutting of samples to a small size, the environment changes which can affect strength. When the specimens are dried at a constant temperature over a period of a few weeks, a smaller specimen may be drier than a larger one. Therefore, the moisture content of different size
14、 specimens cannot be constant. Also, the moisture content of a larger specimen will be less homogeneous from its centre to its surface in comparison to a smaller specimen.Bieniawski (1968) conducted in situ compression tests of sixty cubical coal specimens having edge dimension from 0.019m to 2.012m
15、 underground. He classified the tests into three groups, a small size (up to 0.076 m), a medium size (up to 0.457 m) and a large size (up to 2.012 m). He showed -that compressive strength decreases with increasing specimen size and becomes constant when it reaches the critical specimen size (about 1
16、.524 m), and suggested three different equations for different sizes of specimen as follows:a) Initial constant strength relationship (0(;=constant). For this case a specific value was not given for the edge dimension and other , investigators have found significant variations in strength with sizes in this region (Evans 1970). Different methods were employed to prepare these 3 groups which probably have affected the results obtai
