ABSTRACT
The large diameter TBM tunnelling project planned in the soft ground encountered numerous technical challenges related to settlement control and tunnel stability, necessitating the application of innovative engineering solutions. The large diameter TBM tunnelling is planned with the complex geology of Old Alluvium and Kallang Formation beneath major infrastructure facilities, so the face pressure calculation in design stage and the face pressure control in operation stage, along with excavation management to control ground settlement, were essential. To improve the reliability of muck reconciliation in the EPB TBM equipped with a Belt Conveyor System, advanced volume and weight checking methods were implemented. And additional on-site soil tests inside tunnel were carried out for every ring advance to respond promptly to soil type changes. During cutterhead intervention in soil ground, cutterhead contact force monitoring was used to assess the soil relaxation of the tunnel face. For the construction of the sump pit straight under the tunnel, an innovative bracing design scheme incorporating curved struts and D-frames were utilized to minimize soil loosening while ensuring the logistics control further into the tunnel for achieving constructability of concurrent activities during segment opening.
