The Kowloon Southern Link (KSL) is a 3.8 km underground railway project in a busy urban areawith complex geological and alignment constraints.Akey challenge for the project is to construct a critical sectionof the tunnels above the existing MTR tunnels and below a heavily trafficked road junction, which is termed asthe MTR Crossing. Cut and cover method was originally envisaged to construct the MTR Crossing. In view ofthe complex ground conditions and other physical site constraints, the contractor proposed to extend the boredtunnels using a tunnel boring machine (TBM) across the existing MTR tunnels as an alternative. Adopting theTBM method for the MTR crossing introduced specific challenges which called for comprehensive engineeringstudies, extensive ground treatment, tailored protective measure for the MTR tunnels, as well as sophisticatedinstrumentation in order to ensure that the railway operations and the public safety are not compromised. Thispaper is to discuss the design development of the scheme and the methodology of the MTR Crossing.
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