ABSTRACT
Despite MTR’s no objection to the use of the microtunnelling method from railway protection point of view, there were drawbacks of this method. It is recognized that hand mining in soft ground, in particular in marine deposits and below groundwater table, is a high risk activity. The risks of hand mining include the indirect support system, instability of mined face, potential for seepage and piping through the gaps between horizontal pipe piles, and the likelihood of large ground movements resulting in a risk of damaging existing utilities. To mitigate these risks, substantial ground treatment would be required for the micro-tunnelling construction at the MTR crossing. Furthermore, excavation by hand mining with staged installation of temporary supports and construction of the permanent tunnel structure would be time consuming.
