Comparison of some different formulae for ground shock prediction

In connection with a minor revision of the Norwegian Fortification handbook some different formulae for ground shock predictions are compared. The formulae predict very different values for the strength of the ground shock. The difference can partly be explained by a more detailed consideration of the two different propagation modes of the ground shock. The pulse propagates as a Rayleigh wave close to the surface and as an ordinary compression and shear wave at time distance from the surface. The Rayleigh wave extends deeper into the ground in rock than it does in soil. For that reason it is recommended to use different formulae for ground shock in rock and in soil. The remaining uncertainty in the predicted ground shock strength is mainly caused by the natural variation in geological conditions at different sites. The great uncertainty in the ground shock formulae has generally led to an overprediction of the shock strength and to unnecessarily expensive requirements for ground shock protection. More realistic and less expensive ground shock protection requirements were obtained as a result of this study.