Soil identification by vibration measurements during dynamic penetration testing : a field study

The identification of soil and rock in connection with dynamic penetration tests of hard soils, boulders and rock often requires the retrieval of samples. The process is, however, time-consuming and expensive. A more efficient and cheaper dynamic penetration test for the investigation of dense and hard soils or rock is soil-rock sounding. Only limited information of the soil and its properties is retrieved by this method. For soil-rock sounding a percussion drill is operated in a frequency range between 15 and 30 Hz. During penetration, the impacting drill generates continuous vibra-tions, which propagate as waves to the ground surface. This paper describes a new concept, called Jb-Vib, where the vibrations generated by this impacting drill are measured at the ground surface. The objective is to evaluate whether additional quantitative information can be gained which de-scribes the properties of the penetrated material. The vertical and horizontal components of the vibration velocity are recorded with vibration sensors from which the variation of vibration amplitude and the frequency content with depth can be determined. The RMS-value of the vibration velocity and the frequency spectrum can be derived as a function of depth. Furthermore the effect of geometric damping - the decrease of vibration amplitude with distance – can be accounted for. Prior studies suggest that an important parameter, which can help to identify the type of penetrated material, is the fre-quency content of the signal. Spectrograms can be used to present the variation of frequency and signal intensity as a function of depth. It is shown that the frequency content reflects the material which is penetrated by the impacting drill.QC 20220404