Abstract
In ports and waterways, the bathymetry is regularly surveyed for updating navigation charts ensuring safe transport. In port areas with fluid-mud layers, most traditional surveying techniques are accurate but are intrusive and provide one-dimensional measurements limiting their application. Current non-intrusive surveying techniques are less accurate in detecting and monitoring muddy consolidated or sandy bed below fluid-mud layers. Furthermore, their application is restricted by surveying-vessels availability limiting temporary storm- or dredging-related bathymetrical changes capture. In this chapter, we first review existing non-intrusive techniques, with emphasis on sound techniques. Then, we give a short review of several seismic-exploration techniques applicable to non-intrusive fluid-mud characterization and monitoring with high spatial and temporal resolution. Based on the latter, we present recent advances in non-intrusive fluid-mud monitoring using ultrasonic transmission and reflection measurements. We show laboratory results for monitoring velocity changes of longitudinal and transverse waves propagating through fluid mud while it is consolidating. We correlate the velocity changes with shear-strength changes while the fluid mud is consolidating and show a positive correlation with the yield stress. We show ultrasonic laboratory results using reflection and transmission techniques for estimating the fluid-mud longitudinal- and transverse-wave velocities. For water/mud interface detection, we also use distributed acoustic sensing (DAS) and distributed temperature sensing (DTS).
Highlights
Safe navigation through fluid mud is increasingly important because enhancing the navigability with less dredging can help lower transportation costs and benefit biodiversity
We show the results from the distributed acoustic sensing (DAS) and distributed temperature sensing (DTS) measurements. 3.1 P- and S-waves velocities in the fluid mud from transmission measurements with ultrasonic transducers We examine the first arrivals of transmitted P- and S-waves and estimate their velocity variations during the consolidation of the fluid mud
By examining the change in arrival time of the first S-wave arrival (Figure 7a), we find that the S-wave traveltime decreases with consolidation time, indicating that the S-wave velocity increases with the consolidation progress (Figure 7b)
Summary
Safe navigation through fluid mud is increasingly important because enhancing the navigability with less dredging can help lower transportation costs and benefit biodiversity. Fluid mud is a crucial factor when determining the nautical depth (nautical bottom). It is typically defined by a density value [2]. The Port of Rotterdam uses the density of 1.2 kg/L as a nautical-depth criterium. Other parameters are though used – for example, the Port of Emden adopts the yield stress of 100 Pa to define the nautical depth [2, 3]. It is important to have an accurate parameter that description of the fluid mud and could be used in the same way in different ports
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