  The paper presents a numerical method for simulating flow and mechanics in
fractured rock. The governing equations that couple the effects in the rock
mass and in the fractures are obtained using the discrete fracture-matrix
approach. The fracture flow is driven by the cubic law, and the contact
conditions prevent fractures from self-penetration. A stable finite element
discretization is proposed for the displacement-pressure-flux formulation. The
resulting nonlinear algebraic system of equations and inequalities is decoupled
using a robust iterative splitting into the linearized flow subproblem, and the
quadratic programming problem for the mechanical part. The non-penetration
conditions are solved by means of dualization and an optimal quadratic
programming algorithm. The capability of the numerical scheme is demonstrated
on a benchmark problem for tunnel excavation with hundreds of fractures in 3D.
The paper's novelty consists in a combination of three crucial ingredients: (i)
application of discrete fracture-matrix approach to poroelasticity, (ii) robust
iterative splitting of resulting nonlinear algebraic system working for
real-world 3D problems, and (iii) efficient solution of its mechanical
quadratic programming part with a large number of fractures in mutual contact
by means of own solvers implemented into an in-house software library.
