Dr. Sylvia Stegmann

Sedimentary stability is a controlling factor for denudative and tectonic processes.
Marine sediments consist on grains (solid phase) and fluids (water, gas) in between the pore space, which depends on the compaction of the sediment. An increase of consolidation means a reduction of pore space. If during compaction an adequate drainage is not allowed, overpressured sediments occur. Geological processes causing overpressuring are (i) high rates of sedimentation in fjords, estuary, deltas or deep-sea trenches, (ii) tectonic, tidal, glacial loading, (iii) dissociation of gas hydrates, (iv) groundwater flow and/or (v) dehydration of minerals. Overpressure produces a decrease of effective stress, which may be result in destabilisation of the sediments. In addition to pore pressure, sedimentary strength (as a function of mineralogical composition) is a controlling parameter, which defines soil stability.

At the RCOM, we developed two marine free-fall penetrometer, which can be operated in 200 m (shallow-water lance) and up to 3200 m (deep-water lance) waterdepth, to measure the stiffness and pore pressure of marine sediments in situ. Both instruments are based on standard industrial 15cm²-CPT cones. During insertion of the lance, sedimentary force, acting against the lance, cohesion (cone resistance, sleeve friction) and ambient pore pressure (=measured pressure – (hydrostatic + lithostatic pressure)) are profiled. Dissipation of pore pressure after insertion of the probe can be observed. These measurements can be used to derive crucial geotechnical parameters, e.g. undrained shear strength, permeability.
The shallow-water lance is characterised by its modular concept, which allows a variation of the length with 1m-extension rods up to 6.5m as well as of the weight with 15kg-pieces (40kg-170kg). Depending on the sediment different penetration depth can be reached. This relative easy-handling tool can be deployed from different platforms without an huge effort, including also long-term measurement up to 12 hours.
According to the required period for deep-sea applications, the deep-water lance is operated via telemetry, which provides a realtime-data-transfer and power supply. This probe is equipped with a differential pore pressure system with pore pressure ports directly on the cone and 60 cm above.

If you are interested in an article, please let me know, I will send it to you.

Manuscripts

• Stegmann, S., Strasser, M., Anselmetti, F. & Kopf, A. Geotechnical in situ characterization of landslide deposits: The role of pore pressure transients versus frictional strength. submitted
• Strasser, M., Stegmann, S., Bussmann, F., Anselmetti, F.S., Rick, B. & A. Kopf. Quantifying subaqueous slope stability during seismic shaking: Lake Lucerne, Central Switzerland, as model for formerly glaciated ocean margins, submitted.
• Kopf, A., Alves, T., Heesemann, B., Kaul., N.E., Kock, I., Krastel, S., Reichelt, M., Schäfer, R., Stegmann, S., Strasser, M., Thölen, M. (2006). REPORT AND PRELIMINARY RESULTS OF POSEIDON CRUISE P336, Heraklion - Heraklion, 28.04. – 17.05.2006.
• Stegmann, S., Moerz, T., Kopf, A., 2006. Initial Results of a new Free Fall-Cone Penetrometer (FF-CPT) for geotechnical in situ characterisation of soft marine sediments. Norwegian Journal of Geology 86/03, pp. 199-208.
• Stegmann, S., Kopf, A. & H. Villinger (2006). Design of a Modular, Marine Free-Fall Cone Penetrometer, A Time and Cost-Effective Device for In-Situ Geotechnical Characterization of Marine Sediments, Sea Technology 47/02, pp.27-33.
• Stegmann, S., Kopf A. & H. Villinger (2006). A new modular marine free-fall CPT, European Operational Oceanography: Present and Future, Proceedings of the 4th international Conference on EuroGOOS, pp. 150-153

Poster & Oral Presentation

• Stegmann, S., Strasser, M., Anselmetti, F. & A. Kopf (2006). A Conceptual Model of Pore Pressure as Trigger of Subaqueous Landslides based on in situ Measurements, AGU 2006, San Francisco. (Poster)
• Stegmann, S., Strasser, M., Anselmetti, F. & A. Kopf (2006). In situ-measurements and geophysical characterisation to identify trigger mechanism of earthquake-induced subaqueous mass movements in Lake Lucerne, Switzerland, GV International Conference 2006, Potsdam. (Oral Presentation)
• Stegmann, S., Anselmetti, F., Strasser, M. & A. Kopf (2006). Geophysical characterization and in situ-measurements of earthquake-induced landslide deposits in Lake Lucerne, Switzerland, 66. Jahrestagung der deutschen Geophysikalischen Gesellschaft 2006, Bremen. (Oral Presentation)
• Sylvia Stegmann & Achim Kopf (2006). In situ - characterisation in marine slope sediments with lightweight CPT Instruments, EGU 2006, Vienna. (Poster)
• Kopf, A. & S. Stegmann (2005). The concept of a marine Free-fall CPT systems revisited, AGU 2005, San Francisco. (Poster)
• Stegmann, S., Mörz, T., Villinger, H. & A. Kopf (2005). In situ-Measurements of Geotechnical Parameters – Design and Application of a New Marine Free-Fall CPT, 2nd. International Conference Submarine Mass Movements and their Consequences 2005, Oslo. (Poster)
• Stegmann, S., Kopf, A. & H. Villinger (2005). A new Free-fall-CPT for Marine Application, EUROGOOS 2005, Brest. (Poster)
• Stegmann, S., Schrottke, K. & A. Bartholomä (2005). Seabed Mapping of the inner and outer Weser Estuary, Northwest Germany, EGU 2005, Vienna. (Poster)

• 2004-now
  PhD Student at Research Center Ocean Margin (RCOM) in Marine Geotechnics
  “Development of a marine free fall CPT for geotechnical measurements of (strength and pore pressure) of marine sediments.”
• 2004
  Diploma (=MSc): Side-scan sonar mapping of fluvial sediments in the Weser estuary and their dynamics
• 2001-2004
  Physical Geography w/ focus on Marine Geology, University Bremen
• 1998-2001
  Physical Geography w/ focus on Physics and Remote Sensing / Ludwig-Maximilian University (LMU) Munich
• 1997-1998
  Social Geography / Technical University Munich (TUM)