  We present the results of a new spectroscopic and photometric survey of the
hot, binary X-ray cluster A115 at z=0.193, containing a radio relic. We combine
galaxy velocity and position information to select 85 galaxies recognized as
cluster members (from 115 galaxies observed at TNG telescope), determine global
dynamical properties and detect substructures. We find that A115 presents
velocity dispersion of sigma_v=1362_{-108}^{+126} km/s. Our analysis confirms
the presence of two structures (A115N and A115S) of cluster--type well
recognizable in the plane of the sky and shows that they differ of ~2000 km/s
in the LOS velocity. We estimate that A115S is slightly dynamically more
important than A115N having sigma_v=900-1100 km/s vs sigma_v=750-850 km/s.
Moreover, we find evidence for two small groups at low velocities. We estimate
a global cluster virial mass of 2.2--3.5 e15 h_70 Msun. Our results agree with
a pre--merging scenario where A115N and A115S are colliding with a LOS impact
velocity Delta v~1600 km/s.The most likely solution to the two--body problem
suggests that the merging axis lies at $\sim 20$ degrees from the plane of the
sky and that the cores will cross after ~0.1 Gyr. The radio relic with its
largest dimension perpendicular to the merging axis is likely connected to this
merger.
