Recent Experience with Squeezing Rock in Alpine Tunnels

Tunnelling through brittle fault zones requires special considerations during all phases of a
tunnel project from design to construction. The geotechnical problems during construction
relate primarily to the substantial heterogeneity of fault zones in terms of geotechnical
properties of the rock mass. Geotechnical aspects of fault characterisation and problems of
investigating a tunnel in a fault zone are discussed. It is demonstrated that a technical and
economical optimisation of construction can only be achieved by a flexibility requirement
within the contractual set-up, which allows for adaptation of excavation and support to the
conditions encountered on site. In this context it is emphasised that based on a continuous
evaluation of geological and geotechnical monitoring data, the predicted geological model is
adjusted to the actual conditions. Based on the updated model, excavation and support can
be adjusted accordingly. The principal geotechnical difficulties and adequate measures
during excavation related to tunnelling in brittle faults are discussed. The development of
software to collect and interpret data, tools to aid the decisions on site, as well as up to date
supports for fault zones are demonstrated by case studies of shallow and deep tunnels.