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

本研究的目的是了解干湿循环条件下岩石强度劣化的机理，如何建立岩石强度的评价方法，并根据岩石内部结构，如孔隙度、孔径分布、比表面积和裂隙等，提出判断风化等级的技术指标。这些结果表明，所有的岩样都存在崩解劣化现象。3)通过水银压力法获得了样品的孔隙率和孔径分布。从印尼试件和国内试件的比较来看，印尼试件的孔径分布与国内试件相似，但总孔洞体积大于国内试件。4)在干湿循环条件下测试后的力学性能，如无侧限抗压强度、巴西强度和杨氏模数，比干试件低1/2~1/3。特别是有些试件因崩解现象而无法进行力学试验。我们现在正在考虑如何评价这些类型岩石的特征。5)内部裂缝和孔洞的可视化是通过X射线CT进行的。对于50-100μm的裂缝和孔洞大小，只能进行定性的可视化评价。

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.