| The study on acoustic properties of marine sediment is an important field of oceanography, geology and marine engineering. By analyzing the relationships of physical & mechanical properties and acoustic properties, and then inverting the former with the latter, we can provide basic information and reference to geotechnical environment assessment, marine sediment classification and sedimentology.The Southern Yellow Sea is a shelf sea,rich in oil and gas. Systematic studies on geological and engineering environment of The Southern Yellow Sea have been carried out, but studies on acoustic properties of marine sediment are few. This paper chooses the seafloor sediment samples from the typical area in the central of The Southern Yellow Sea. Through the in-situ sound speed measurement and laboratorial analysis, we get a mass of data about physical and mechanical properties and acoustic properties of seafloor sediment.This paper analyzed 345 groups'sediment samples from 85 sites and obtain the physical & mechanical properties including grain composition, natural density, water content, void ratio, liquid and plastic limits, shear strength and acoustic properties including compressed wave velocity, compressed wave attenuation. According to statistical analysis of measured data, this paper found that the study area is mainly clay sediments with the characteristics of high moisture content, large void ratio, large plasticity, high compressibility and low shear strength, and the sediment is not the ideal foundation soil.Laboratorial experimental analysis showed the compressed wave velocity of the sediment in the central of The Southern Yellow Sea is smaller than that Hamilton get from continental shelf sediments, but is similar with the results Lu Bo get from East and South China Sea. Overall, compressed wave velocity becomes larger along the sediment particles are bigger. The compressed wave attenuation coefficient varies greatly, and is smaller than that Lu Bo get from shallow sea sediments of South China Sea. The paper analysis of the distributions of compressed wave velocity and attenuation under six frequency conditions of 25kHz, 50kHz, 100kHz, 150kHz, 200kHz and 250kHz, but no significant dispersion found.This paper focused on the relationship between the physical & mechanical properties of sediments and the compressed wave velocity measured in laboratorial. The regression equations were established on basis of the relationships. Comprehensive analysis showed that sediment compressed wave velocity was high correlated with natural density, natural water content, porosity, and plasticity characteristics and the positive correlation coefficients were about 0.9. With compressed wave velocity, shear strength has no correlation, but compression factor is well negative correlated, and the average size has a positive correlation. This paper also established the two parameters equation with compressed wave velocity and physical properties. Using natural density and plasticity index or void ratio and liquid limit as independent variables, and compressed wave velocity as dependent variable, it can get a better analysis results by this two-variable regression, and the correlation coefficient also is higher.The one-parameter equation used the average size, density, void ratio as independent variables give good results, which is similar with Hamilton's results. Compared to Anderson, Liang Yuanbo and Lu Bo's research, the approximation is less. The equation used water content as independent variables give different results from Lu Bo's.By contrasting the compressed wave velocity measured in situ with that measured in laboratory, there was difference, but also correlation between them. And compressed wave velocity measured in laboratory always larger than compressed wave velocity measured in situ. The Pearson correlation coefficient of them was 0.93. If there is more data, it is possible to establish the relation of the compressed wave velocity measured in situ and that measured in laboratory, then we can invert the physical & mechanical properties with the compressed wave velocity measured in situ. |
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