A study of time-dependent properties and other physical properties of rocks
AuthorSingh, Devendra Pratap
Document TypePhD thesis
CitationsSingh, D. P. (1970). A study of time-dependent properties and other physical properties of rocks. PhD thesis, Mining Department, The University of Melbourne.
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© 1970 Dr. Devendra Pratap Singh
The strength and deformation behaviour of rocks are time-dependent. Therefore the design of rock structures underground should be based on the long-term strengths rather than the strength determined by short-term laboratory tests. The direct method of determining the long-term strength of a rock is tedious and time consuming. Hence it is considered important that short-term methods of predicting long-term strengths of rocks be evolved. Short-term methods based on measurement of volumetric strain, stress-strain, log stress-log strain and loading rate were investigated. The long-term strength of Sicilian marble was determined by the direct method and was found to be close to the predicted long-term strengths by short-term methods. With the equipment used in this project, the leading rate method proved to be quicker and more accurate than other short-term methods as the processing and plotting of data were not involved in this case. The volumetric strain method predicted higher time-dependent strengths than the direct method. Dilatancy was observed in many intact rock specimens tested in uniaxial compression. It was also found that the values of Young's modulus and Poisson's ratio of a specimen are stress-dependent. All the three stages of the idealized creep curve i.e. transient, steady state and accelerated stage, were observed in Sicilian marble and Wombayan marble specimens. The lateral creep rate in the above two marbles was found to be larger than the axial creep rate at sustained stresses greater than their yield stresses. In the triaxial tests, in which only Sicilian marble specimens were tested, the ratios of predicted long-term strength to maximum strength showed a declining trend with increasing confining pressures. In the study of friction along the fractured surfaces of Sicilian marble specimens in the triaxial tests, it was found that during sliding the sheer stress and normal stress on the sliding plane have a straight line relationship. The average coefficient of friction for Sicilian marble was found to be 0.84.
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