花コウ岩大型ビームの長期たわみ実験の13年間の実験結果および湿度変化に対する修正

抄録

This paper is the third report following up the first and the second, the first having been published in “Jour. Soc. Materi. Sci. Japan, ” Vol. 14, p. 507, and the second in the same journal, Vol. 17, p. 925.
Our experiments were started on Aug. 7, 1957 in a basement laboratory of the Geological and Mineralogical Institute, Kyoto University. Owing to the reconstruction of the Institute buildings, the test-pieces had to be removed (very carefully) on Oct. 14, 1967 to a distantly located laboratory in the Kyoto University compounds, where the experiments have been carried on likewise for nearly 3 years up to date (Aug., 1970).
The deflection curve of the test-piece is represented by y=T(t)·X(x), where T(t) is a function of time t that has a reciprocal dimension of Young's modulus E and T(O)=1/E. From T(t) we can derive S(t) which is the sag of the central point. Plotting the values of T(t) against t, it is found that the moving of the test-pieces produces no abrupt change in the general trends of T(t) for both the center-loaded and unloaded beams (the two test-pieces). In the general trend the values of T(t) of both the beams increase very slowly with the time for the whole period of 13 years. This impels us to postulate that granite undergoes viscous flow or plastic flow that has a very small yield stress.
It has been already metioned in our second report that the mean curves of T(t) show clear dependence on humidity for the first 5 to 10 years. The range of annual changes in the humidity in the old laboratory was 35% to 85%, but less range of 75% to 95% has been shown in the new laboratory. Accordingly T(t) obtained there does not show so clear dependence on humidity as T(t) did in the old laboratory. In the later part of this paper is given the report of the examination of the correlations between T(t) (and S(t)) and humidity for the first 5 to 10 years. It is found that the correlation coefficients in S(t) for both the beams are nearly equal. In Fig. 6 are shown the graghs of T(t) corrected for humidity. The general trend of the T(t) is almost the same when correction has been made regarding humidity as that before correction, indicating that the correction for change in humidity does not sensibly affect the values of viscosity.
In the previous reports it is reported that, from the beginning, minute folds have been formed on the upper surfaces of both the test-pieces. It is confirmed in this paper that the mean amplitude of the fold has been very slowly increasing, as shown by the variation of ε (Fig. 4), for each test-piece during the whole period of 13 years.