The described work has been carried out on October 2013 by the Istituto Nazionale di Ricerca Metrologica (INRiM) of Turin (Italy), in collaboration with the International Timescales with Optical Clocks (ITOC) project. The experimental results of the absolute measurement of the free-fall acceleration g in the Laboratoire Souterrain de Modane (LSM), along the Frejus tunnel between Italy and France are reported. The measurements have been performed with the transportable absolute gravimeter IMGC-02 of the INRIM in a site which will be used to install an optical clock. With this instrument a relative accuracy of few parts in 109 is reachable, i.e. measurement of g with uncertainty of tens microgals (1 μGal = 1 × 10−8 m s−2).