Abstract

A 580 m long access tunnel (arbetstunnel Torsgatan) is currently being constructed as part of the City Line tunnel project in Stockholm. The bedrock along the tunnel alignment was investigated in 2004 and a prominent fault zone was identified. Results from 3D geological modelling indicated that the fault zone was aligned parallel with the access tunnel and would intersect a 17 m deep open cut with anchored sheet pile walls above vertical rock slopes. The open cut was considered a sensitive construction due to the close proximity of a piled bridge foundation, high speed rail lines and a heavily trafficked road. Planar and toppling failure was identified as possible failure mechanisms in the south and north rock slopes respectively and a preliminary reinforcement design was included in the tender documents. The preliminary design was successfully implemented in the construction phase after geological mapping and observation of support performance.

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