No abstract

In order to clarify the fatigue failure process of shirahama sandstone, fatigue tests were done, and deformation characteristics and AE occurrence behavior were investigated. Then, the strength of specimens, which loading and unloading were repeatedly applied to for some times, and crack development in them were examined.In the fatigue test, fatigue failure occurs in the comparatively short time (about 3.5 days), when upper limit stress corresponds to the stress at stage C of uniaxial compression failure process, where the volume of the rock specimen expands. The fatigue failure process are divided into three stage (I, II, III) from change in strain and AE activity. Lowering the strength of the rock specimen begins from stage II of fatigue failure process, and it is in a good correlation with the increase in lateral / axial strain ratio. The value of b obtained from the relationship between AE event frequency and AE energy of each event decreases when macroscopic cracks develop in the specimen.

It is commonly known that water-saturated rock increases in strength due to freezing of pore water when cooled. This increase in strength due to freezing obviously appears in rock with relatively high porosity. It is also known that water-saturated rock increases in thermal diffusivity due to freezing of pore water when cooled. Despite its relatively high porosity, however, frozen tuff does not increase in thermal diffusivity. In this study, we considered the presence of clay minerals and investigated the influence of pore water on the mechanical properties of water-saturated rock under low temperatures. Specifically, we put a specimen of Ogino tuff and that of Berea sandstone through a uniaxial compression test and an indirect tensile test in a temperature range of-170°C to room temperature. Our findings are as follows. The influence of pore water on the strengthening mechanism of water-saturated rock under low temperatures needs to be investigated separately on bulk water and interlayer water. The strength of water-saturated sandstone is presumed to result from the interaction between a load distribution effect due to freezing of bulk water and an increase in the strength of ice due to cooling after the freezing of bulk water. In water-saturated tuff, since interlayer water does not freeze, the load sharing effect due to freezing is not expected to contribute to the strength of the rock. Therefore, it is necessary to design a new model.

The purpose of this study is to develop a method of measuring thermal diffusivity in rock core and rock mass by the