| Budget Amount *help |
¥2,100,000 (Direct Cost: ¥2,100,000)
Fiscal Year 1995: ¥200,000 (Direct Cost: ¥200,000)
Fiscal Year 1994: ¥1,900,000 (Direct Cost: ¥1,900,000)
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| Research Abstract |
Firstly, measurements of compressive and shear wave velocities are carried out by downhole and refraction wave propagation techniques at dam site composed of Diatomaceous mudstone to estimate the distributions of in situ velocities. The compressive wave velocities obtained from both downhole and refraction methods increase linearly with depth, whereas the shear wave velocities increase in proportion to a function of the power of 1/6-1/7 of depth, which is different from the distribution of velocities measured at an embankment.
Secondly, observations of micro tremor are also conducted to anticipate the eigen frequency at same site. The predominant frequency observed is 0.3Hz, so that the depth of suface deposit is estimated about 400m using above-mentioned distributions of shear wave velocities.
Thirdly, to investigate the deformation characteristics in small strain region, both triaxial compression (UU) and dynamic tests are performed in cylindrical specimens of Diatomaceous mudstone prepared in vertical and horizontal directions with mechanical anisotropy. The results obtained are as follows :
(1) Specimens with the higher strain level exhibit the greater anisotropy as reflected by the ratio between the horizontal to vertical Young's moduli.
(2) The dynamic test results indicate that the strain dependency of Young's modulus in vertical direction exists to some degree even at 10^<-6> strain level.
Finally, the seismic risk analysis is performed employing the distribution of annual maximum acceleration with an upper bound limit at above-mentioned site, obtained from a theory of extremes using seismological data. As a result, it is shown that the acceleration value expected during 100 years is 160gal, which is about the same as the present design ground acceleration, whereas the upper limit acceleration value is about 450gal ; this must be taken into account in the eartquake resistant design.
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