A common geotechnical site investigation method in Sweden is soil-rock sounding. A steel rod is driven into the ground by a percussion drill and different drilling parameters are recorded. The penetration speed and pushing force are used to determine the soil layer profile, the presence of boulders, and the depth to bedrock. This article describes a novel concept where the ground vibrations generated by the drill bit are measured by a geophone at the ground surface to gain more information about the penetrated material. The results of vibration measurements are analyzed in terms of frequency spectra, spectrograms, and two new parameters called “spectral concentration” and “overtone ratio.” These results show that the method can identify the depth of the groundwater table, distinguish boulders from penetration into bedrock, and possibly identify silt, sand, and gravel layers. More data are needed in different soil types to verify the reliability of the concept.

Dynamic penetration tests are frequently used as geotechnical site investigation methods. In Sweden, the main reason to choose a dynamic penetration method is to investigatedepth to bedrock, strength and deformation properties of soil, compaction, or pilingdepth. The advantage of dynamic penetration methods is that they have a betterpenetration ability than static methods and it is therefore easier to penetrate hardmaterial or rock.The most common dynamic penetration method in Sweden is soil-rock sounding. Duringsoil-rock sounding, a metal rod is drilled into the ground and measurements are taken ofdepth, drilling resistance, sinking speed, feeding force, hammer pressure, and rotationalspeed and pressure. The method is conducted in different classes with varying accuracies.Soil-rock sounding is mainly used to determine depth to bedrock, but as the drilling rodpenetrates the whole soil layer profile, there may be opportunities to gain moreknowledge about the penetrated material using the same process.The scope of this licentiate research project was to investigate whether vibrationmeasurements on the ground surface performed simultaneously with soil-rock soundingcan yield additional information about the soil layer profile and the thin layers within amaterial. Measurements were conducted in various building and infrastructure projectsin eastern Sweden between Norrköping and Stockholm/Solna and the results wereanalyzed. It was investigated whether there is a relationship between the vibration resultsand soil properties as determined by other geotechnical investigation methods in thesame area.The results show that soil-rock sounding with simultaneous vibration measurementsconstitutes a promising extension of the conventional soil-rock sounding method whichcan provide additional information about the soil layer profiles at the investigation site.Furthermore, indications can be made about overall soil layer profiles. However, thevibration signals must be adjusted due to distance attenuation before results fromdifferent depths, boreholes and sites are comparable.

The different penetrated materials and their properties are correlated to the frequencycontent of the vibration signal. In this way, more information about the penetratedmaterial can be gained from the vibration measurements. The results show thatheterogeneities in the penetrated soil layer can clearly be seen in the vibration results andpatterns in these heterogeneities identified. Furthermore, the results indicate that thevibration signals can help to distinguish silt from sand/gravelly soil and boulder from rock,and the ground water table can be seen in the frequency spectrogram for granular soils.

Dynamiska sonderingsmetoder är vanliga geotekniska undersökningsmetoder. Den främsta anledningen till att välja dynamiska sonderingsmetoder i Sverige är när djup till berggrund, hållfasthets- och deformationsegenskaper av olika jordar, packning eller påldjup ska undersökas. Fördelen med dynamiska sonderingsmetoder är den bättre genomträngningsförmågan jämfört med statiska metoder. På så sätt är det enklare att sondera genom hårt jordmaterial eller berg.

Den mest vanliga dynamiska sonderingsmetoden i Sverige är jord-berg-sondering. Vid jord-berg-sondering används en borrstång för att sondera marken och parametrar som djup, borrmotstånd, sjunkningshastighet, matningskraft, hammartryck liksom rotationshastighet och -tryck registreras. Metoden genomförs i olika klasser med olika noggrannheter. Jord-berg-sondering används huvudsakligen för att bestämma djup till berggrund men med tanke på att metoden genomtränger hela jordlagerprofilen vid undersökningsplatsen finns det en stor möjlighet att erhålla mer information om det genomträngda materialet i samband med jord-berg-sondering.

Målet med detta forskningsprojekt var att undersöka om man kan erhålla ytterligare information om jordlagerföljden och förekomsten av tunna lager inom ett material när vibrationsmätningar på marken genomförs samtidigt som jord-berg-sondering. Mätningar genomfördes i ett flertal byggnads- och infrastrukturprojekt mellan Norrköping och Stockholm/Solna i östra Sverige och resultaten analyserades. Korrelationen mellan resultaten av vibrationsmätningarna och jordegenskaperna som utvärderades genom andra geotekniska undersökningsmetoder vid samma försöksplats.

Resultaten visar att jord-berg-sondering med parallella vibrationsmätningar utgör ett lovande tillägg till den konventionella metoden där man kan erhålla ytterligare information om jordlagerprofilen vid undersökningsplatsen. Vibrationssignalerna måste dock justeras på grund av avståndsdämpning innan resultaten från olika djup, olika borrhål och olika undersökningsplatser kan jämföras mot varandra.

De olika genomträngda materialen och deras egenskaper korreleras mot frekvensinnehållet av vibrationssignalen. På det sättet kan ytterligare information om det genomträngda materialet erhållas från vibrationsmätningarna. Resultaten visar att heterogeniteter av det genomträngda jordlagret ses tydligt i vibrationsresultaten och att olika mönster kan identifieras. Utöver det indikerar resultaten att vibrationssignalerna kan hjälpa till att skilja mellan silt och sandiga/grusiga jordar och mellan block och berg. Grundvattennivån kan identifieras i frekvensspektrogrammen för friktionsjordar.

Bei modernen Vibratoren können die Vibrationsfrequenz und das exzentrische Moment während des Rammens verändert werden. Das dynamische Zusammenwirken der schwingenden Bohle mit dem umgebenden Boden kann durch Feldmessungen untersucht werden. Bisher wurde der Einfluss der Vibrationsfrequenz auf den Eindringvorgang und die Ausstrahlung von Vibrationen in die Umgebung nicht ausreichend beachtet, obwohl die Frequenz für die Rammbarkeit und die Erschütterungsausbreitung von Bedeutung sind. In vorliegendem Beitrag werden die Ergebnisse von drei Proberammungen beschrieben, bei denen Doppelbohlen in einen mitteldichten kiesigen Sandboden einvibriert wurden. Messungen wurden am Vibrator, an der Spundbohle und im Boden durchgeführt, womit u. a. die Frequenz, die Schwingungsamplitude, die Eindringgeschwindigkeit der Bohle und die Bodenerschütterungen registriert wurden. Eine Analyse der Messwerte zeigt, dass die Schwingungsfrequenz ein wichtiger Parameter ist. Wenn die Bohle nahe der Resonanzfrequenz des Vibrator-Bohle-Bodensystems erregt wird, schwingt die Bohle in Phase mit dem umgebenden Boden. In diesem Zustand sinkt die Eindringgeschwindigkeit ab, während die Vibrationsausstrahlung in den Boden ansteigt. Die Resonanzfrequenz kann einfach durch Messung der Bodenschwingungen bestimmt werden. Effektives Vibrationsrammen wird erreicht, wenn die Vibrationsfrequenz deutlich höher als die Resonanzfrequenz ist. Vibrationsmessungen zeigen, dass durch das Absenken des exzentrischen Moments stärkere Bodenerschütterungen verursacht werden können.

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.

There are many different methods to retrieve information about ground properties prior to building and infrastructure projects. In Sweden the most common method is soil-rock sounding (Jb-sounding) which was developed in Norway in the 1990s. Soil-rock sounding is used for identifying the stratification of soil and the depth to bedrock and can be applied in different classes with different accuracy. It is an effective method with low costs but gives restricted information about the penetrated soft soil strata sequences and its properties. Improved knowledge about the presence of different soil and rock layers is necessary for a cost-effective design particularly of deep foundations.

The purpose of this research project is to perform vibration measurements on the ground during soil-rock sounding to gain more knowledge about the penetrated ground. The measurements can be executed without influencing or affecting the sounding measurements and show that the frequency content of the signal is reflecting the properties of the penetrated soil layers. As an important step for developing the new measurement method vibration measurements with an accelerometer are compared to simultaneous measurements with a geophone in order to evaluate which sensor is most suitable for retrieving soil information. The results and recommendations of this analysis are presented in this paper.

A common geotechnical site investigation method in Sweden is soil-rock sounding. A steelrod is driven into the ground by a percussion drill and different drilling parameters arerecorded. The penetration speed and pushing force are used to determine the soil layer profile,the presence of boulders, and the depth to bedrock. This paper describes a novel conceptwhere the ground vibrations generated by the drill bit are measured by a geophone at theground surface to gain more information about the penetrated material. The results ofvibration measurements are analyzed in terms of frequency spectra, spectrograms, and twonew parameters called “spectral concentration” and “overtone ratio”. These results show thatthe method can identify the depth of the groundwater table, distinguish boulders frompenetration into bedrock, and possibly identify silt, sand and gravel layers. More data areneeded in different soil types to verify the reliability of the concept.