A case study on design and construction of mined tunnel in challenging ground conditions in Singapore

This paper presents a case study on design and construction of mined tunnel for DTSS2 in Singapore. The geological condition comprises excavation in soft soil, hard rock as well as unexpected fault zone with high water permeability. The analysis methods for mined tunnel in rock used included the Q-system, analytical closed-form calculations, kinematic analysis using the Unwedge software, while the analysis method for mined tunnel in soil was carried out using finite element method with ground stress relaxation assessment. Mechanical excavation with hydraulic breakers and excavators were adopted for construction of the mined tunnel. Probe drilling and grouting were carried out to form a water-tight zone surrounding the tunnel profile. Convergence points were installed and monitored to ensure the movement of the mined tunnel is within design limit. The excavation of the mined tunnel has completed in March 2022, the maximum convergence of mined tunnel recorded was well within the design work suspension level.