Ground Motion Relations While TBM Drilling in Unconsolidated Sediments

The induced ground motions due to the tunnel boring machine (TBM), which has been used for the drilling of the urban metro tunnel in Karlsruhe (SW Germany), has been studied using the continuous recordings of seven seismological monitoring stations. The drilling has been undertaken in unconsolidated sediments of the Rhine River system, relatively close to the surface at 6–20 m depth and in the vicinity of many historic buildings. Compared to the reference values of DIN 4150-3 (1–80 Hz), no exceedance of the recommended peak ground velocity (PGV) limits (3–5 mm/s) was observed at the single recording site locations on building basements during the observation period between October 2014 and February 2015. Detailed analyses in the time and frequency domains helped with the detection of the sources of several specific shaking signals in the recorded time series and with the comparison of the aforementioned TBM-induced signals. The amplitude analysis allowed for the determination of a PGV attenuation relation (quality factor Q ~ 30–50) and the comparison of the TBM-induced ground motion with other artificially induced and natural ground motions of similar amplitudes.