Shape effect and rock stiffness evaluation for a TBM launch shaft in limestone
On a stormwater project in the Middle East, which supports sustainable urban development and climate resilience, a 30 m deep TBM launch shaft in limestone has been designed as a 36 m long shaft with 26 m long straight walls and rounded ends with 5 m radius. The paper provides an overview of the design of the temporary shotcrete lining with rock bolts, which was based on 2D plane strain numerical analyses for the straight walls and axisymmetric numerical analyses for the rounded ends. The design was supplemented with 3D numerical analyses. Based on a sensitivity study in 2D and based on the difference in results between 2D and 3D models, the effect of rock stiffness and the shape effect of the shaft was evaluated by comparison with convergence measurements. Good agreement with the monitoring results was found when considering these effects.