Acoustic Soil-Rock Probing : A Case Study in Gubbängen

Abstract: Soil-rock probing (Jb-probing) is the most common probing method in Sweden. Due to the penetration capacity of the Jb-probing it can be performed in both soil and rock. However, the capacity also results in inherent limitations and uncertainties, such as the difficulty identifying the soil layer sequences of soft soils. In order to attain a more detailed soil layer sequence it is necessary to perform complementary probing and sampling methods, an inefficient and consequently costly procedure. By instead implementing non-interfering complementary methods performed simultaneously as the Jb-probing the method may be rationalized. The so-called acoustic Jb-probing method may be a potential complement to the Jb-probing. In this thesis a continued study of the acoustic Jb-probing method is performed by means of a case study in Gubbängen with the focus on the potential additional information that the spectrogram (a visual representation of the frequency spectra) may contain compared to the Jb-parameters alone. This was done by obtaining vibration signals during Jb-probing using a triaxle geophone installed four meters from the boreholes. Vibration signals were collected from 13 boreholes. The vibration signals were then analyzed in time- and frequency domain which were compared to corresponding Jb-parameters and classified soil types. The results showed that the clay layers held the most promise for discovering additional information in the spectrogram, however this does not exclude potential in other soil types. Additionally, it was shown that the geophone ought to be fastened in the ground in order to attain satisfactory data. Overall, the acoustic Jb-probing method is a favorable way of collecting and analyzing data, which with continued development of the operational and computational process may be an economical alternative to the conventional method.