Abstract
Seabed surveying is the basis of engineering development in shallow waters. At present, geophysical survey methods mainly utilize sonars for qualitative surveying, which requires the calibration of the results found through in situ drilling and sampling. Among them, the parameters required for engineering designs are obtained from either in situ tests or laboratory experiments of soil samples retrieved from drilling. However, the experience from onshore applications shows that the physical quantities obtained through quantitative geophysical survey methods for shallow waters can be indirectly used to estimate engineering parameters or directly as parameters for engineering evaluation, which has high application potential. This review analyzes various geophysical survey methods for nearshore site characterization (i.e., side-scan sonar, single/multi- beam sonar, sub-bottom profiler, seismic reflection method, and underwater magnetometer) and challenges in their application, and introduces quantitative geophysical survey methods (including the underwater seismic refraction method, seismic surface wave method and underwater electrical resistivity tomography) that are worth focusing on for future development. Three application difficulties have been identified, namely, the lack of operational efficiency, appropriate operational equipment and systems, and sufficient guidance for experimental shallow sea applications. It is hoped that comprehensive discussion of these challenges will increase awareness leading to engineering improvements in the surveying and measuring capabilities in shallow waters, further reducing the risk of geotechnical hazards.
Highlights
With the increasing reliance on the coastal and marine environment, more construction is being carried out, including the development of underwater foundations for existing bridges, sea tunnels or ports, as well as offshore wind farms, floating cities, and tidal stream generators, in an attempt to meet the needs for energy and living environments
The results obtained in the second category of geophysical survey methods can identify the interface where the physical quantity changes; these methods include the use of side-scan sonar, single/multi-beam sonar, sub-bottom profiler, seismic reflection method, and ground-penetrating radar
Archie [7], Biella et al [8], Klein and Santamarina [9], and others have suggested a highly linear relationship between formation factor and porosity; soil conductivity can be used to estimate hydraulic conductivity ([8,10]). Based on these theoretical findings, an increasing number of cases have recently emerged in which shallow water geophysical methods of the third category have been applied in different engineering surveys: Punzo et al [11] used the imaging profiles obtained from the underwater seismic refraction method to create a 3D model of harbor sediment and estimate its volume for use in further dredging planning
Summary
Human development moved from the plains into the mountains, yet with the demand for marine resources, this development is currently actively expanding to coastal and offshore areas. Eng. 2022, 10, 344 seabed depth and landforms, it is an important application to determine the geological conditions under the seabed, using reflected waves from sonar signals, which determine material changes qualitatively and assist in evaluating the geologic structure with minimum drilling data. These common shallow water geophysical survey methods mainly provide changes interfacequalitatively information, areinunable to provide its structure engineering material andbut assist evaluating the geologic withproperties. Many quantitative survey techniques can still be applied, such as underwater drilling data These common shallow water geophysical survey methods mainly provide seismic refraction andbut electrical resistivity tomography [1].
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