Vibration Transfer Mobility Measurements Combining Falling Weight and Impact Hammer Excitation Methods

For construction in an urban environment, vibration transfer mobility measurements are useful when developing detailed prediction of ground-borne vibration and ground-borne noise for underground or surface rail transit systems. These measurements typically use a large impact hammer to generate impulses in the soil and an array of accelerometers or velocimeters to measure the vibration response to the impulses. The correlation between the force and the vibration results is used to characterize the transfer function of the ground in a localized area.

The effectiveness of this approach is limited by the amplitude of the force impulse when dealing with larger zones and SSI attenuation, especially for larger buildings, where a satisfactory signal-to-noise ratio cannot be achieved with traditional methods. In some of these cases, a seismic vibrator truck can be deployed on site, but site specific constraints do not always make this possible.

To address these shortcomings, a double stage measurement method has been developed by using a “weight drop” approach combined with the impact hammer.

The methodology that combines the processes of the two impulse-inducing methods and controls the uncertainty of the measurement chain is presented in this paper. The technique will be detailed and an application case on a shaft of the “Grand Paris Express” project will be presented with emphasis on the added value for the parties involved.