Dr. Manman Hu Department of Civil Engineering, HKU
As the demand for energy worldwide keeps increasing, a potential engineering induced damage to the environment causes wide public concerns. New geo-energy technologies (e.g. unconventional shale gas, enhanced geothermal systems) need to incorporate intrinsic mechanisms to prevent negative impact to the environment, strategically inserted into the process from the design to the implementation phase, and hence warrant sustainable usage of energy resources. This type of approach in geomechanics is distinct from the classical one for the fact that it emphasizes the coupling of hydro-mechanical behavior of the geomaterial with the natural and engineered environment – including the temperature, chemical concentrations, mineral dissolution/precipitation, and other physical variables.
Dr. Hu’s research group has been focusing on tackling the fundamental multi-scale (in both space and time) multi-physics problems of environmentally assisted crack propagation, with a long-term goal to control the effectiveness of treatment techniques and the extent of chemical footprint. This presentation consists of three parts. First, Mode I (opening mode) subcritical cracking is studied with an emphasis on the effect of the chemical environment. In particular, two constitutive frameworks, namely reactive-chemo-plasticity and reactive-chemo-elasticity, that allow the coupling of chemical mass removal (occurring on the solid-fluid interface at the micro-scale) into the plastic and elastic domain of rock behavior via different mechanisms, are developed and assessed. Subsequently, studies on Mode II (sliding/shear mode) cracking are presented via multi-physics modeling of shear instability and bifurcation through a damage mechanics implementation. Localized shear deformation around a borehole due to internal pressurizing (e.g. by fluid injection) is investigated and the role of temperature is emphasized. The third part of this presentation discusses chemo-hydro-thermo-mechanical instabilities in geomaterials and the emergence of localized patterns triggered by cross-diffusion waves that involve internal mass transfer and/or phase transformation.