Nina Stark

Detection and quantification of sediment remobilization processes using a dynamic penetrometer

Sediment remobilization processes have a high impact on coastal morphology as well as offshore engineering. In many cases countermeasures are required to preserve the stability of the construction or coastline. To apply such countermeasures in the most effective manner, it is crucial to (i) locate and map areas of sediment erosion and deposition and to (ii) quantify the mobilized sediment with a high spatial and temporal resolution. In this study we tested the small dynamic penetrometer Nimrod as a tool for rapid detection and quantification of sediment remobilization processes. More than 20 surveys with about 5000 deployments covered natural-induced sediment remobilization processes such as shifting sandbars and sorted bedforms as well as man-induced processes such as the siltation in navigation channels and scour. The surveys were carried out in areas of different sediment textures ranging from soft clay to hard quartz and carbonate sands. Additionally, preliminary experiments under controlled boundary conditions were accomplished in a wave channel (Franzius Institut, Hannover, Germany).

In Situ Localization and Quantification of Sediment Deposits after Dredging and Disposal Interventions in Sydney Harbour, Canada, Using a Dynamic Penetrometer

In late 2011, more than 4.2 million cubic meters of seafloor sediments dredged from the central channel of Sydney Harbour (Nova Scotia, Canada) were relocated to a coastal site near Edwardsville, on the west side of the South Arm of the harbor. Dynamic penetrometer measurements were carried out in October 2012 for rapid geotechnical characterization, localization, and quantification of dredged material deposits, using the lightweight dynamic penetrometer Nimrod . Complementary sediment samples and digital images were taken at selected positions using a small grab sampler and underwater camera. Sydney Harbour is characterized by a large variety of sediment types. Muddy sediments ranging from low to moderate consolidation states were found, as well as compacted fine sands. The dynamic penetrometer results allowed the localization and quantification of deposited dredge disposal material in a cost- and time-efficient manner. The spatial distribution of sediments is in good agreement with a sediment dynamics model by CBCL Limited. However, the deposited sediment layers were thicker than anticipated, being on the order of 10-20 cm, and reaching several tens of centimeters when mixed with finer, muddy deposits.

LIRmeter: A new tool for rapid assessment of sea floor parameters. Bridging the gap between free-fall instruments and frame-based CPT

Physical and geotechnical parameters of marine sediments are of vital interest to fields like foundation-planning of offshore structures, surveying of cable routes, sediment dynamics, sediment manipulation (dredging, plowing), ground-truthing of acoustical surveys, risk assessment and mine burial predictions. Therefore, characterization of geotechnical in-situ parameters with dynamic penetrometers is of interest for research, consulting and the offshore industry, because in-situ methods, and especially dynamic tests, are generally less time consuming than static tests or measurements on samples. In addition, recovery of sediment samples from the seafloor may alter the sediment characteristics (pressure decrease, temperature change) and limits the information value. To date, the determination of fundamental parameters like shear strength, bearing capacity or grain size is predominantly done ex-situ. However, in-situ assessment of these parameters leads to a better characterization of marine sediments due to direct measurement under field conditions.