Attenuation and broadening of georadar signals in moist sandy- clayey soils was modeled depending on clay content and moisture of a soil. Antennas are of the slot type and are situated on the face of a tunneling machine. The pulse, radiated and received by this antennas and reflected by a perfectly conducting layer or small dielectric objects, was considered. Modeling has been carried out by integral equation method. For given signal to noise ratio the maximum distance of sounding have been calculated. The distance of sounding has been considered depending on size of the antennas, duration and shape of source pulse. The shape of signals depending on distance of sounding and soil parameters have been studied. To find dielectric permittivity of soils in wide frequency range a simple model was used, which takes into account the conductivity of the soil, dipole water relaxation and very wide spectrum of relaxation frequencies in clayey soils, which is due to Maxwell-Wagner effect in clay. Dielectric permittivity of several clayey soils, taken from tunnels, has been measured, and the model of soil has been adjusted with these experimental data.