Abstract: Forecasting tunnel’s geological conditions using forward procedures of GPR (ground penetrating radar) provides interpretation basis, improves the accuracy of interpretation and helps avoid accidents. Currently most forward modellings are focused on the tunnel lining, but less on the surrounding rock in front of the working face.Through theoretical forward simulation by establishing large-scale geological model together with low-frequency antenna, we conclude that 1) the effective forecast distance is about 30m by using low-frequency antenna of 50MHz; 2) GPR could accurately identify the depth and shape of fracture zone, caves and other geological bodies, and cophase axis of reflected waves is consistent with that in theoretical model; 3) the variation trend of dielectric constant of surrounding rock in the front could be obtained from the wave phase and amplitude changes of single-channel data; 4) the electromagnetic waves attenuate more rapidly in complex model, and the simulation result is weaker than that of single geological model. Finally, we give two application examples to verify the forward modelling and provide a reference for reflected waves with the same shape.

Key words: tunnelling engineering , advance forecast, GPR, finite difference, forward simulation