| Budget Amount *help |
¥3,600,000 (Direct Cost: ¥3,600,000)
Fiscal Year 2002: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 2001: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 2000: ¥2,300,000 (Direct Cost: ¥2,300,000)
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| Research Abstract |
1. Theoretical analysis
The frequency characteristics of the radiation impedance of the circular vibrating plate for high porosity marine sediment such as Hedoro sediment layer were investigated. The relationship between the porosity, the concentration and the shear wave velocity of Hedoro sediment were considered.
2. Experiments
(1) the shear wave velocity of gelatin which is seemed to be the medium with very slow shear wave velocity just same as high porosity Hedoro sediment were measured using the radiation impedance method. The concentration of gelatin was changed from 2.5% to 50%. From the measured results, it is seen that the shear wave velocity increases, as the concentration increases. It is also seen that the very slow shear wave velocity (0.07m/s) can be measured using the radiation impedance method.
(2) The shear wave velocity of 1) Kaolin suspension, 2) Kibushi clay, 3) Seabed sediment of off-Kouchi port, 4) Seabed sediment of Shimizu port were measure using the radiation imped
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ance method. From the measured results, it is seen that the shear wave velocity increases, as the porosity decreases, for all sediment models. However, the porosity characteristics of the shear wave velocity are dependent on the kind of the medium. This results is considered due to the reason that the grain size, the grain shape and the structure of the frame of the sediment models are different, even though the porosity is the same.
3. Development of a measuring system
(1) It is necessary to measure the shear wave velocity rapidly in situ. A method for obtaining the radiation impedance rapidly by inputting the pulse responses of the force pickup and the accelerometer to a FFT analyzer was investigated. It is seen that the measured results using the pulse response method is almost agreed with that using the sinewave response method.
(2) The vibrator with the force pickup and the accelerometer was set in the specially ordered waterproof vessel. The sensor cables and the vibrator driving cables were waterproofed. Moreover, the device to avoid the extra force to the force pickup was done.
The prospects for the in situ measurements of the shear wave velocity of Hedoro sediments using the measuring system are obtained. Less
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