Failure mode transition in brittle Boudinage: effects of cohesion, mean stress and layer thickness in discrete element models and field examples

Many aspects of the evolution of boudinage are still poorly understood, and using boudins as rheology-gages is in its infancy. The aim of the study is to achieve a better understanding of the evolution of boudinage by numerical mechanical modeling integrated with three-dimensional characterization and analysis of natural boudinage structures. We use results from a 3D field study of boudins as a basis for high resolution numerical modeling.

We use the computationally expensive 3D Discrete Element method to model the boudinage process from loading to strain localization and post failure deformation in parametric studies using high resolution and a realistic representation of the coupled brittle and ductile deformation processes. This provides quantitative insight into the acting mechanisms and coupled processes during the formation of boudins to link the large variety of boudin geometries to specific boundary conditions. In particular we show that the transition from blocky torn boudins to drawn boudins can be modeled as a function of material strength and confining pressure. Furthermore, local heterogeneities can cause shear failure already before the critical stress is reached in the entire rock volume

The numerical simulations are augmented by studies on a world class example of boudinage structures on the island of Naxos, involving an extensive field study, detailed 3-dimensional reconstruction of boudinage structures and microstructural investigation of the underlying deformation processes.

Our ultimate goal is to pave towards a mechanically meaningful 3D boudinage classification scheme that allows for quantitative analysis of boudinage structures in order to invert boudin geometry to the kinematics and rheology of the rock during its deformation, as well as to its stress and strain history.