Design and dynamic analysis of a pneumatic impulse generating device for the non-destructive testing of ground anchorages

This paper describes the design and dynamic analysis of an impulse-generating device which has been developed for use as part of a system to test ground anchorage systems non-destructively. The device is a relatively simple pneumatically operated design similar in function to a small air hammer working under computer control. An accelerometer attached to the device provides the measurement function. Results from the testing system are presented which show that in some cases the response of the anchorage to the input is a complex spectrum of frequencies. A dynamic model of the device, including the pneumatic system, is presented and results from this indicate that multiple impacts are occurring within the device during the measurement period. Analysis of the frequency spectrum of a two impulse force input is presented and using a single degree of freedom system and a previously developed and validated model of a ground anchorage, it is shown how the two impulses can produce the type of response exhibited by the test result from an anchorage. Some possible mechanical and signal processing solutions to mitigate the problem are presented.