ESR-9-01

Micro-mechanics of failure planes

Ricarda Gatter | Marum

Research

Almost 20 years ago, in July 1998, a tsunami struck Papua New Guinea and devastated three villages, causing the death of over 2200 people. In 1996, a landslide initiated offshore Finneidfjord, Norway, and removed a 250 m long section of the main north-south highway, due to the slide’s retrogressive behaviour. Although these events highlighted the importance of submarine landslide research, the potential hazard related to submarine landslides was already recognised in 1929. A large slide and the flow of sediment it generated broke telecommunication cables off Grand Banks. However, to enable the assessment and effective mitigation of this hazard, one needs to understand the underlying mechanisms first. What causes submarine landslides? What are the pre-conditioning factors and triggering mechanisms? How do submarine landslides behave during runout?

I focus on the factors that pre-condition slope failure. Many stud­ies have shown that basal fail­ure planes of sub­mar­ine land­slides co­in­cide with mech­an­ic­ally weaker lay­ers em­bed­ded within the slope strati­graphy. Pore pres­sure fluc­tu­ations along po­ten­tial weak lay­ers, e.g. em­bed­ded vol­canic ashes or fos­silifer­ous soils whose particles can break down un­der load­ing, can de­crease the shear strength of the sed­i­ments and hence, un­der­mine slope sta­bil­ity. Al­though many stud­ies have assessed the influence of sed­i­ment com­pos­i­tion on the phys­ical prop­er­ties and shear strength of sediments, the processes oc­cur­ring prior and dur­ing the ini­tial fail­ure are still poorly un­der­stood, as these can­not be dir­ectly ob­served or mon­itored. In this project, I will conduct a number of 3D numerical shear experiments, utilising granular simulation techniques (e.g., PFC3D), to investigate the failure processes at the initial stages of submarine landslides.

Methods

In a first step, I will compile a comprehensive dataset of µ-CT (micro- Computed Tomography) measurements of a wide range of sediment cores from different submarine landslides. These include cores from the Finneidfjord Slide (Norway), the AFEN Slide (UK), the Twin Slides (Italy), the Cap Blanc Slide (NW Africa), and the Tuaheni Slide (New Zealand). From this dataset, I will gather compositional and textural information of the material near the basal failure planes of the slides. The resulting information will directly act as input data for the numerical models.

By means of the 3D numerical simulations, which mimic geotechnical shear tests on a micro-(grain)-scaled level, I will investigate the fabric evolution of different materials under shearing with time. Of particular interest will be (A) a simplified ash and (B) a diatom sediment, and the changes in their shearing behaviour due to variations in the ash and diatom contents. The grain-scaled level is necessary in order to discern the spatial and temporal evolution of shear zones. Where does strain accumulate and where do basal failure planes form (above, inside, or below the weak layer)? This information is necessary to gain a deeper understanding of the failure mechanism and hence, the slide evolution itself.

Hosting institute
 
 
Working Group
  • Modelling of Sedimentation Processes
PDP Committee members:

TEAM

Ricarda Gatter
MARUM
PhD student – ESR 9
rgatter@marum.de
Homepage
Katrin Huhn-Frehers
MARUM
Principal Investigator – ESR 9, 11
khuhn@marum.de
Homepage

NEWS

GLOMAR – the Bremen International Graduate School of Marine Sciences
Courses, ESR 11, ESR 7, ESR 9, News | 2018-12-04
 

Graduate schools can provide PhD students valuable support in a variety of ways. In this blog, Ting-Wei (ESR 7), Ricarda (ESR 9) and Monika (ESR 11) introduce GLOMAR, the international graduate school for marine sciences in Bremen. Read more about networking opportunities, seminars and offered courses!

Ricarda’s report on her 2nd secondment
@ NOCS / University of Southampton

ESR 9, News, Secondments | 2018-06-19
 

After a first, shorter secondment at NOCS and the University of Southampton in February, Ricarda returned to Southampton in May to continue her work on µCT (micro-Computed Tomography) data, focussing in particular on data from the AFEN Slide (UK) and the FInneidfjord Slide (Norway).

Review of ECORD Training Course 2018
@ MARUM, Bremen, Germany

ESR 11, ESR 2, ESR 3, ESR 4, ESR 6, ESR 7, ESR 9, News | 2018-06-18
 

From 23rd to 27th April, a group of seven SLATE ESRs participated in the ECORD Training Course 2018, which took place at MARUM – Center for Marine Environmental Sciences, Bremen. This one-week course provided a “Virtual Ship Experience” and prepared the young researchers for sailing in an offshore drillship expedition.