A Device for the Measurement of Sub-Surface Ground Vibrations

A reliable measurement of free-field stress waves from transient loading has several important applications, for example, in the design of effective wave barriers to protect sensitive equipment and in the design of underground protective structures against explosive loading, to name a few. The characteristics of a stress wave are highly dependent on the energy source and the soil medium through which it propagates. A new device in place of a buried sensor is described in the present paper that can be used to measure the free-field sub-surface ground vibrations in the horizontal direction. Laboratory modal analyses showed that the device has a natural frequency of about 600 Hz. For practical applications, the upper frequency limit of the device is taken as 300 Hz, which is well above the range of frequencies normally encountered in practice. Test measurements using both the device and buried sensors in residual soils from an impact load and a blast load are presented. Evaluation of the test results shows that the characteristics of the stress waves generated by these loads can be measured accurately with the device. Compared to a buried sensor, the device has the added advantages of ease of alignment to the source and ease of retrieval.