Study on rock strength deterioration and weathering for soft and semi-hard rocks in dry-wet cyclic conditions

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The subjects of this research is to understand about the mechanism of the deterioration of rock strength in the dry-wet cyclic conditions, how to establish an evaluation method of them and to suggest a technical guideline to judge a grade of the weathering by the internal structures of rock such as porosity, distribution of the diameter of pores, the specific surface areas and cracks.The outline of this research is as follows :1) It is understood that the mechanical properties of measures rocks such as shale that were collected from Indonesian and domestic coal mines.2) The slaking phenomenon was examined by the slaking observation method and the ISRM suggested method. Those results show the slaking deterioration was recognized for all rock specimens. The extent of slaking deterioration of Indonesian specimens was larger than that of domestic specimens.3) The porosity and the distribution of the diameter of pores of specimens were obtained by the mercury pressure method. From the comparison between the Indonesian specimens and the domestic specimens, the distributions of the diameter of pores of Indonesian specimens are similar to that of domestic ones, however, the total volume of the pores of Indonesian ones are larger that domestic ones.4) The mechanical properties such as the unconfined compressive strength, the Brazilian strength and Young's modulus after testing in the dry-wet cyclic conditions were 1/2 to 1/3 lower than those of dry specimens. Specially, some specimens for the mechanical testing could not be obtained due to slaking phenomenon. We are now considering how to evaluate the characteristics for those types of rocks.5) Visualization of the internal cracks and pores was carried out by the X-ray CT.It is possible to evaluate only the qualitative visualization for the sizes of 50-100 μ m of cracks and pores.