Construction process induced vibrations on underground structures

Vibrations produced on the ground surface by engineering construction processes can damage underground structures. At present there is little knowledge of the level of surface vibrations that could cause damage to underground structures. The relevant British Standards, BS 5228 and BS 7385, have little reference to underground structures. Investigation of the soil-underground structure interaction, under ground borne vibration, must be carried out in a geotechnical centrifuge where prototype stresses and strains are recreated in the model. In this paper we discuss preliminary findings based on 1g experiments on small-scale models. Even though these tests were carried out at low stresses, useful information on the interaction aspects of underground structures was obtained. Experiments were carried out at 1 g in a sand model instrumented with an array of miniature accelerometers around two model tunnel inclusions with brass and plastic tunnel linings. Impulsive and harmonic loadings were produced on the sand model surface by a drop hammer mechanism and an electric eccentric-mass motor respectively. The propagation of waves in dry sand and the vibration levels in model tunnels under both the impulse and harmonic surface loading were investigated.