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Some implications of empiricism and assumptions in laboratory testing
ARTICLE IN PRESS
International Journal of Rock Mechanics & Mining Sciences 41 (2004) 374
SINOROCK2004 Paper 1A 19
Some implications of empiricism and assumptions in laboratory testing H. Abdullah*, A.K. Dhawan Central Soil & Materials Research Station, New Delhi, India
Abstract Some implications of approximations introduced by empiricism and/or assumptions in the laboratory assessment of rock are highlighted with the help of discussions on three topics: * * *
correlation between uniaxial compressive strength and point load strength index; the use of triaxial compression test data for assessment of c, f, m and s parameters (Fig. 1); and evaluation of dynamic elastic parameters (based on wave velocities).
In the case of correlation between point load strength index and uniaxial compressive strength, our submission is that the universal correlation of 20–25 is highly misleading, and the database for the same needs to be specified; also, the instances of different correlation factors need to be specified, so that one knows which cases one can realistically utilize this correlation. The case of assessment of c, f, m and s parameters is to show that, in a given case, one or the other theory may or may not be applicable. And, there could also be situations when none of the existing theories may be applicable, and one might have to improvise. In the third case of evaluation of dynamic elastic parameters, based on wave velocities, the objective is to highlight that in certain cases the theories, practices, and/or the empirical relations normally adopted may not be applicable when the underlying assumptions do not hold good; and unacceptable distortions are introduced if these are used. The paper presents alternatives to deal with the discussed atypical situations. The submission is that ingenuity is called for to assess a rock; and the assessment must be holistic. Two things need to be made mandatory: to communicate the test data to a centralized place, so that suggested relations can be re-examined; and to declare the database on which any relation is based. Keywords: Rock; Laboratory; Assumptions; Empiricism; Static; Dynamic
Granitic Gneiss
Axial Stress (MPa)
200
150
100
50
0 0
2 4 Confining Pressure (MPa)
6
Fig. 1. Strength envelope. *Corresponding author. E-mail addresses: [email protected] (H. Abdullah), [email protected] (A.K. Dhawan). For full length paper see CD-ROM attached. doi:10.1016/j.ijrmms.2003.12.095
International Journal of Rock Mechanics & Mining Sciences 41 (2004) 374
SINOROCK2004 Paper 1A 19
Some implications of empiricism and assumptions in laboratory testing H. Abdullah*, A.K. Dhawan Central Soil & Materials Research Station, New Delhi, India
Abstract Some implications of approximations introduced by empiricism and/or assumptions in the laboratory assessment of rock are highlighted with the help of discussions on three topics: * * *
correlation between uniaxial compressive strength and point load strength index; the use of triaxial compression test data for assessment of c, f, m and s parameters (Fig. 1); and evaluation of dynamic elastic parameters (based on wave velocities).
In the case of correlation between point load strength index and uniaxial compressive strength, our submission is that the universal correlation of 20–25 is highly misleading, and the database for the same needs to be specified; also, the instances of different correlation factors need to be specified, so that one knows which cases one can realistically utilize this correlation. The case of assessment of c, f, m and s parameters is to show that, in a given case, one or the other theory may or may not be applicable. And, there could also be situations when none of the existing theories may be applicable, and one might have to improvise. In the third case of evaluation of dynamic elastic parameters, based on wave velocities, the objective is to highlight that in certain cases the theories, practices, and/or the empirical relations normally adopted may not be applicable when the underlying assumptions do not hold good; and unacceptable distortions are introduced if these are used. The paper presents alternatives to deal with the discussed atypical situations. The submission is that ingenuity is called for to assess a rock; and the assessment must be holistic. Two things need to be made mandatory: to communicate the test data to a centralized place, so that suggested relations can be re-examined; and to declare the database on which any relation is based. Keywords: Rock; Laboratory; Assumptions; Empiricism; Static; Dynamic
Granitic Gneiss
Axial Stress (MPa)
200
150
100
50
0 0
2 4 Confining Pressure (MPa)
6
Fig. 1. Strength envelope. *Corresponding author. E-mail addresses: [email protected] (H. Abdullah), [email protected] (A.K. Dhawan). For full length paper see CD-ROM attached. doi:10.1016/j.ijrmms.2003.12.095