ABSTRACT
Tunnel portals are subject to key risks that may significantly impact tunnel construction including floods by adjacent streams or rivers, landslides from unstable overlying overburden, rockfalls from unstable rock blocks that were not stabilized, and avalanches in cold climate regions where deep snow is present. The control and management of groundwater infiltration is one of the most important requirements during tunnel construction since inundation of a tunnel can result in significant damage to equipment and also impact the stability of the tunnel and the safety of workers. Probe drilling is a very effective mitigation measure that provides additional information during tunnel construction. The result of probe drilling should be documented in longitudinal sketches or drawings during construction and discussed with the tunnel constructor to convey the possible risks ahead and develop plans for mitigation measures accordingly. Tunnel seismic prediction has become a commonly utilized tool for risk management during tunnel construction to plan mitigation measures and minimize overall project delays.
