  A range of phenomena in the subsurface is characterised by the interplay
between coupled thermal, hydraulic and mechanical processes and deforming
structures such as fractures. Modelling subsurface dynamics can provide
valuable phenomenological understanding, but requires models which faithfully
represent the dynamics involved; these models, therefore are themselves highly
complex.
  This paper presents a mixed-dimensional thermo-hydro-mechanical model
designed to capture the process-structure interplay using a
discrete-fracture-matrix framework. It incorporates tightly coupled
thermo-hydro-mechanical processes based on laws for momentum, mass and entropy
in subdomains representing the matrix and the lower-dimensional fractures and
fracture intersections. The deformation of explicitly represented fractures is
modelled by contact mechanics relations and a Coulomb friction law, with
particular attention on coupling of fracture dilation to the governing
equations in both fractures and matrix.
  The model is discretised using multi-point finite volumes for the balance
equations and a semismooth Newton scheme for the contact conditions and is
implemented in the open source fracture simulation toolbox PorePy. Finally,
simulation studies demonstrate the model's convergence, investigate
process-structure coupling effects, explore different fracture dilation models
and show an application of the model to a 3d geothermal pressure stimulation
and long-term cooling scenario.
