Micro-Macro Modeling of Chemo-Mechanical Damage and Healing in Rocks- Xianda Shen

Where: 
Cherry Emerson Building 204
When: 
Wednesday, October 9, 2019 - 12:00

 

Abstract:

In rock mechanics, damage and healing refer to the degradation and recovery of stiffness and strength induced by the evolution of microscopic defects. The gap between microscopic and macroscopic models makes it difficult to bridge the defects characterization at the microscopic scale to the development of deformation and stiffness at the macroscopic scale. Therefore, the goal of this doctoral research is to understand and predict damage and healing processes in rock, by coupling microstructural and poromechanical models.

In the first part of the thesis, we present micro-macro approaches to model the influence of micro-crack propagation on the accumulation of damage and irreversible deformation in salt rock. Fabric tensors are defined as moments of probability of solidity, grain coordination, local solid volume fraction and crack volume. The evolution of fabric tensors correlates with that of macroscopic mechanical properties. Additionnally, we found that deformation is dominated by grain rearrangement. We formulated, calibrated and validated a micro-mechanical model coupled with elasto-plastic model that captures these phenomena, called  a discrete wing crack elastoplastic damage (DWCPD) model. We also formulated a chemo-mechanical homogenization framework to understand the rate dependent behavior of salt rock observed in cyclic compression tests.

In the second part of the thesis, a micro-macro homogenization framework is established to understand the coevolution of chemical weathering of minerals and bedrock weakening. The proposed model quantifies the accumulation of damage in the matrix of bedrock driven by chemical weathering of minerals like biotite, which expand as they weather and create stresses sufficient to fracture rock. This model shows that chemical weathering of minerals is the controlling mechanism of saprolite production.

In the last part of the thesis, a novel multi-scale homogenization model is presented to simulate salt rock healing driven by pressure solution. Hollow sphere inclusions traversed by three inter-granular contact planes are modeled at the microscopic scale. Pressure solution in the inclusions induces the accumulation of chemical strain and the recovery of stiffness of salt rock at the REV scale. We implemented the micro-macro model of healing in the Finite Element Method for simulating carbon dioxide storage in a salt cavern. Based on thermodynamic principles, a generalized thermo-hydro-chemo-mechanical framework is also proposed to model multiple processes of damage and healing.

Advisor

Dr. Chloé Arson

Committe Members:

Dr. Susan Burns
Dr. Sheng Dai
Dr. Ken Ferrier (University of Wisconsin Madison)
Dr. Ting Zhu (ME)