Effect of accounting rockbolts in the numerical analysis on the surface settlements of Steinhaldenfeld tunnel

The Steinhaldenfeld tunnel is located in the north-eastern part of the city of Stuttgart, Germany. The construction of this tunnel was carried out between the Hauptfriedhof and Steinhaldenfeld station, including two cut and cover parts of each 110 m length at the tunnel portals and a conventionally constructed part of 940 m length in between. Several numerical studies have been performed to predict the magnitude of induced surface settlements (Ref. [4], Ref. [6]).Throughout the studies some simplifying assumptions have accounted for modelling of tunnel installation procedures, like assuming a zone with increased cohesion around tunnel instead of modelling of rockbolts. Thus, the reported results from numerical studies differ from what discovered in the field. These differences consist of steepness of the settlement trough, which is more steeped in the case of discovered data, and the magnitude of settlements, which are smaller in the case of field data. This research is focusing on how modelling of rockbolts in the numerical analysis can affect the induced surface settlements and the settlement trough shape. Results indicate that the modelling using rockbolts (instead of grouting zone) yields more accurate surface settlements with regard to the discovered data in the field. However, both modelling cases supply wider settlement troughs with less inclined shape relative to the settlement trough in the field, which means they do not provide conservative results for risk assessment of surface structures.