Modeling rock folding with large deformation frictional contact mechanics

Understanding the mechanics responsible for folding and related fracturing of rocks is critical to the planning and management of activities that have a significant impact on the world's economy because folds are common traps for hydrocarbons and water. This dissertation encompasses the development and numerical implementation of new and existing bulk elastoplastic and interface constitutive models for geologic materials, along with their application to folding of sedimentary rock strata. A framework was developed to capture the salient mechanical features of such geologic structures: elastic and inelastic deformation, discontinuous displacement field, frictional slip and/or opening of interfaces, and large deformation effects. The proposed methodology is novel in that a physics-based numerical technique is used to simulate observed field behavior of complex geologic systems.;An enhanced Matsuoka-Nakai model for bulk elastoplasticity that is capable of modeling rock-like materials was proposed and implemented into a fully implicit finite element code. A key aspect of this work is to model the evolution of existing rock discontinuities in an explicit manner accounting for large deformation effects. A constitutive model for geologic interfaces considering unilateral contact, friction, and adhesion is presented and implemented using an efficient return mapping scheme. This constitutive law extends the Coulomb slip criterion to the tensile regime to capture opening of adhesive interfaces in a quasi-brittle manner.;Numerical models that capture the kinematical aspects of thrust fault related folds induced by regional-scale far-field contraction are presented. Complex fault interactions are considered in terms of how they influence fold geometry. The above modeling technique is utilized to assess contradicting geologic interpretations that can not be observed in nature or replicated in the lab given the scale and nature of these phenomena.;Finally, the reactivation of fractures and bedding-surface slip during the formation of the asymmetric anticline at Sheep Mountain, Wyoming was investigated. Contact mechanics was used to investigate slip or opening of fractures and bedding surfaces and to better constraint the multilayer model. It is demonstrated that the presence of weak bedding surfaces, which are usually present in sedimentary rock strata, play a crucial role in the mechanical development of folds and related fracturing. The results provided by the finite element models correspond with field observations and provide additional insights into the physics of folding and related fracturing processes.