Study of strip-filling for old room and pillar mining goaf
According to the problems of land resources destruction and environmental pollution caused by the collapse of old room and pillar mining goaf, a goaf security evaluation model was established and applied to the safety assessment of a colliery in Ordos city. The results indicated that the room and pillar mining goafs in this coal mine area would fail with time passing. To solve the problems, with analyzing the structural characteristics and activation mechanism of old room and pillar mining goaf, based on the theory of strip mining, a new method of strip-filling for controlling subsidence of old room and pillar mining goaf was put forward and used in designing of the strip-filling plan of the colliery, the filling effect prediction have been worked out. It demonstrates that the strip-filling method is economically feasible.
The significance of in situ tests on large rock specimens
Abstract This paper reviews large scale in situ tests on rock conducted throughout the world. Based on the authors' experience of 8 years of in situ testing involving 66 large coal speciments (up to 2 m in width and height and with width-to-height ratios from 0·5 to 3·4 ), the value and meaning of large scale in situ tests in compression are discussed. Practical guidelines are given for performing the tests, preferred testing techniques are described and typical data to be expected from the tests are listed. Empirical formulae are derived for the presentation of strength results and application of large scale test data to engineering design is demonstrated. It is also shown how the results of such tests can be directly applicable to predicting the behaviour of full size rock structures. Finally, the costs of large scale tests are considered, in terms of both time and money, and actual figures are quoted. It is concluded that large scale in situ tests can be an invaluable aid in engineering design and that their costs constitute a very small percentage of the value of production from an average mine and that the costs of tests are more than offset by the financial returns and technical gains obtained from large scale in situ tests.
The effect of speciment size on the mechanical properties of unjointed diorite
Abstract Mechanical properties of unjointed in situ and laboratory specimens of quartz diorite and granodiorite covering a wide range of specimen sizes were determined under static uniaxial loading conditions. A drill and broach technique was developed to prepare the in situ specimens. In situ specimens were right triangular prisms ranging in length from 1 to 9 ft loaded by a flat-jack system. The laboratory samples consisted of triangular prisms from 4·5 to 12 in. in length and cylindrical specimens 3·18 and 4·25 in. in length. Specimens had a length-to-edge or length-to-diameter ratio of 1·5:1·0 or greater. Maximum stress for the quartz diorite decreased with increasing specimen size by a factor of 10, ranging from 10,000 psi for a 2·0 in. specimen to 990 psi for the 9 ft specimen. Maximum stress asymptotically approached a value of 1000 psi for quartz diorite specimens greater than 3·0 ft in length. All specimens failed in shear and exhibited dilation prior to failure. For the quartz diorite, apparent Young's modulus ranged from 0·322 to 0·645 × 106 psi, apparent Poisson's ratio ranged from 0·10 to 0·33. Neither of these properties correlated well with specimen size. The maximum stress for small specimens of granodiorite averaged 27,700 psi; modulus for both in situ and laboratory samples ranged from 2·27 to 8·33 × 106 psi.