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Process-based approach on tidal inlet evolution – Part 1
Published in C. Marjolein Dohmen-Janssen, Suzanne J.M.H. Hulscher, River, Coastal and Estuarine Morphodynamics: RCEM 2007, 2019
D.M.P.K. Dissanayake, J.A. Roelvink
Grain size variability over sandwaves is observed at several locations of different water depths, sandwave morphology and flow conditions in the North Sea. At five sites, sampling strategies were especially designed to record grain size patterns over sandwaves. Samples were taken at crests, in troughs and in most cases also on the slopes of sandwaves (Figure 1). Sea bed sampling was carried out using a cylindrical box corer, of which sediment cores were resampled on board, except for site 4, where a vibrocorer was used. Grain size distributions of sea bed subsamples were determined in the lab by laser diffraction, using a Malvern 2000, for grain sizes smaller than 2mm after sieving off the coarser material. All samples fall within the sand fraction, i.e. noncohesive sediment. The sandwaves at all sites are compound sandwaves, i.e. sandwaves with superimposed megaripples. They furthermore display migration, with migration rates that differ from site to site.
Defining geotechnical parameters for surface-laid subsea pipe-soil interaction
Published in Michael A. Hicks, Federico Pisanò, Joek Peuchen, Cone Penetration Testing 2018, 2018
A SMARTSURF® system, or equivalent, is preferred for shallow seabed sampling (Table 1). The box corer is a secondary tool. Box core sampling and associated laboratory testing are often used and occasionally misunderstood. This is further discussed below. The other samplers listed in Table 1 typically have Possible Applicability and No Applicability. These classifications relate to reliability of complete sample recovery for the upper 0.5 m BSF. ISO (2014) provides background information about such sample recovery limitations. The penetration capabilities of the box corer limit the effective use of the tool to clays of extremely low and very low strength (Table 1). For these types of soil, the box corer has continuous sample recovery to penetration depth, typically up to 0.5 m BSF. This allows for accurate characterisation of the layering of the upper seabed (Fig. 2). Nevertheless, it is possible that the top material, particularly loose non-cohesive material, is washed out of the sampler when the box corer is retrieved to the vessel. As for all types of non-pressure sampling, total stress conditions inevitably change upon extraction of a sample from the soil. This can lead to soil swelling, loss of saturation and formation of free gas in the sample where gas was previously in solution in the pore water.
Variation of temperature-dependent sound velocity in unconsolidated marine sediments: Laboratory measurements
Published in Marine Georesources & Geotechnology, 2018
Sora Kim, Gwang Soo Lee, Daechoul Kim, Jooyoung Hahn, Woo-Hun Ryang
Figure 8 shows that M4 has a lower sound velocity, although it has a coarser texture than M1. M4 was obtained at a depth of 10 cm in the upper part of the core. As a result, M4 shows high porosity and water content, but its density is low, as in M1. However, grain density is higher than M1 (Table 1). The box core was devised to acquire samples from the uppermost part of the core as it preserves the sedimentary structure well because of low sediment disturbance (Kennett 1982). This is thought to explain the low velocity change of sample M4, despite the high grain density and grain size.