Abstract
Compression and Brazilian tests were carried out under confining pressure without sealing the specimen in order to know the effect of pore water pressure on the strengths of Ogino tuff and Kimachi sandstone. Main results are summarized as follows: (1) The maximum differential stress and tensile strength of Kimachi sandstone when load was applied immediately after setting confining pressure were almost the same as those of under atmospheric pressure. On the other hand, the maximum differential stress and tensile strength of Ogino tuff increased with confining pressure. (2) Unconfined tensile strength of Ogino tuff was not influenced by the confining pressure which was applied and unloaded before the test. Namely, the increase in tensile strength of Ogino tuff, described in (1), was not due to permanent change of the microstructure. (3) In the case of Ogino tuff, the maximum differential stress decreased with the exposed time of confining pressure, and the tensile strength approached to the value obtained under atmospheric pressure with the exposed time. (4) In Ogino tuff, tensile strength parallel to the bedding plane was greater than that vertical to the bedding plane in dry conditions. However, in wet conditions, tensile strength parallel to the bedding plane was smaller than that vertical to the bedding plane. (5) The maximum differential stress and tensile strength of Ogino tuff were smaller in 1N NaCl solution than those in distilled water. Furthermore, the anisotropy in tensile strength observed in distilled water disappeared in the 1N NaCl solution.
