Study on a method of the shear wave velocity in surficial marine Hedoro sediment layer using radiation impedance method

1. 理论分析研究了高孔隙度海洋沉积物（如Hedoro沉积层）中圆形振动板辐射阻抗的频率特性。考虑了Hedoro沉积物孔隙度、浓度与剪切波速的关系。实验(1)用辐射阻抗法测定了与高孔隙度Hedoro沉积物类似的极慢剪切波速介质明胶的剪切波速。明胶的浓度由2.5%变为50%。从测量结果可以看出，随着浓度的增加，横波速度增大。还可以看到，使用辐射阻抗法可以测量非常慢的横波速度（0.07m/s）。(2)采用辐射干扰波速法测量了1)高岭土悬浮液、2)Kibushi粘土、3)口池港外海底沉积物、4)清水港海底沉积物的剪切波速。实测结果表明，所有泥沙模型的剪切波速随孔隙度减小而增大。然而，剪切波速的孔隙度特征取决于介质的种类。考虑这一结果的原因是，即使孔隙率相同，泥沙模型的粒度、颗粒形状和框架结构也不同。测量系统的研制(1)原位快速测量横波速度是必要的。研究了一种将力传感器和加速度计的脉冲响应输入到FFT分析仪中快速获取辐射阻抗的方法。由此可见，脉冲响应法的测量结果与正弦波响应法的测量结果基本一致。(2)将带测力器和加速度计的振动器设置在特制的防水容器中。传感器电缆和振动器驱动电缆都是防水的。此外，该装置避免了额外的力对力的拾取。展望了利用该测量系统进行Hedoro沉积物横波速度原位测量的前景。少

1. Theoretical analysisThe 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 … More 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