A Coupled Thermo-mechanical Distinct Lattice Spring Model for Numerical Modelling of Rock Thermal Fracturing
Fuxin RUI+, Gao-Feng ZHAO#
Tianjin University, China

Rock thermal fracturing is a key issue in the analysis of geothermal development, oil and coal seam gas exploitation, strong electromagnetic wave assisted rock breakage, nuclear waste storage, crustal evolution, etc. The effect of thermo-mechanical coupling is crucial to the propagation and evolution of rock thermal fracturing. Distinct lattice spring model (DLSM) is a discrete element method that discretizes matter into individual particles linked by springs, which has advantages in simulating the dynamic failure and wave propagation in rocks. Nevertheless, it still lacks the ability to deal with multi-physics coupled problems. In this work, the concept of thermal pipe network is adopted in the DLSM to duplicate the corresponding mechanical lattice so that the Fourier’s law can be solved at the pipe level. In addition, the implementation of thermal pipe network in the DLSM is convenient to develop the coupled thermo-mechanical constitutive model for rock failure and to derive the closed form relationship between the macro and micro thermal parameters. The coupling relationship between the thermal and mechanical fields is addressed through the thermal expansion equation. Furthermore, the coupled thermo-mechanical DLSM adopts a dual timeline coupling scheme that the mechanical timeline and thermal timeline can have different time scales, which enables the coupled model to both deal with the transient and steady-state thermo-mechanical coupling problems. Finally, we demonstrate a series of numerical examples to verify the applicability of the coupled thermo-mechanical DLSM.