Generation of Ground Vibrations by Accelerating and Braking Road Vehicles

Generation of ground vibrations by accelerating and braking road vehicles is considered theoretically for vehicles accelerating (decelerating) with a constant acceleration from rest to a constant speed, or braking to a stop from a constant speed. The problem is considered in the low-frequency approximation: an accelerating or braking vehicle is modelled as a point horizontal traction force applied to the ground and moving along with the vehicle. 1/3-octave frequency spectra of the vertical component of the ground vibration velocity are investigated as functions of acceleration, final (initial) speed of the vehicle, ground attenuation, and radiation angle relative to the direction of the vehicle movement. It is shown that for medium and upper bands of the spectra the generated ground vibration level is determined mainly by acceleration and is almost independent of the initial (final) vehicle speed. For low-frequency spectral bands, oscillations of ground vibration amplitudes versus both acceleration and initial speed may take place. These oscillations may he responsible for large statistical deviations of experimentally observed ground vibration levels. In contrast to vehicles travelling on uneven roads, the ground vibrations generated by accelerating and braking vehicles are characterised by directivity patterns which show, in particular, that there is no radiation in the directions perpendicular to the direction of vehicle movement.