Gauvain Wiemer

Geotechnical analysis of marine sediment deformation and failure processes in geodynamically active areas

Submarine slope failures are common along tectonically, seismically and thus oftentimes volcanically active margins. Earthquake shaking is one of the most contemplated triggers for marine slope sediment failure. Due to cyclic shaking excess pore pressure can be induced and may lead to liquefaction of highly porous sediments (i.e. turbidite sands, silts , ash layers...etc.) or to progradational failure of more plastic sediments (i.e. clays). Likewise the occurrence of submarine slope failure without any obvious short term triggering mechanism have been reported. Sudden sediment failure can take place under static condition when peak shear strengths are exceeded by static slope sediment loading. In essence most soils show a different response to periodic loading than to static loading – making static and cyclic loading experiments compulsory for submarine slope stability and mass-movement initiation studies.
My research interest mainly lies in the geotechnical characterization of marine sediments under static and cyclic loading condition using laboratory and in situ geotechnical instruments. A special focus is set on volcanoclastic materials. I use the MARUM Dynamic Triaxial Testing Device (DTTD) to investigate marine sediment's shear strength under cyclic loading conditions. Earthquake shaking of porous sediments, such as sands, silts and tephras is simulated thereby. A direct shear apparatus is used to investigate the static shear strengths. For in situ characterization of sediment's shear strength the free fall Cone Penetration Testing (CPT) device comes into operation.
My research focuses on I) to the liquefaction susceptibility of different types of granular, porous material. Especially ash layers, provided by active margin associated volcanism, are widely discussed as potential glide planes of submarine slides and shall thus be analyzed for their liquefaction suceptibility. II) The prediction of earthquake induced sediment excess pore pressure. And III) the behavior of clay and moreover 'quick' clay under static and cyclic loading conditions. Improving comprehension of marine sediment-failure processes under different loading conditions shall be achieved.