  For a long-term forecast of the average air temperature in a metro tunnel and
surrounding soil, heat balance conditions are modeled in a system that includes
two parallel tunnels, a near-tunnels underground space, the earth's surface and
atmospheric air with seasonal temperature variation. It is assumed that the air
in the tunnels is well mixed, and the thermal effect of ventilation is taken
into account by replacing the air in the tunnels with atmospheric air. The
system of heat balance equations is solved numerically by the finite element
method. A numerical analysis of the influences of the model parameters on the
average temperature in the tunnels and surrounding soil is carried out. The
dimensions of the soil region with an elevated temperature, located between the
tunnels, are estimated.
