Rethinking the Water Leak Incident of Tunnel LUO09 to Prepare for a Challenging Future

Incident often occurs while deepening excavation pit and/or tunnelling underground pipelines although serious attention from practitioners, engineers, and scientists has received. Prevention and mitigation of incident have thus been deemed to be the key in developing sustainable infrastructure in urban areas. This study analyses and discusses an extensive water leak incident taken place throughout the parallel tunnels LUO09 construction in the soft alluvial deposits in Kaohsiung, Taiwan. Dumping sand bags and quick-set cement intervened the incident but in vain. The water leak incident is initiated by the piping. The existing vehicle underpass causes the jet-grout columns installed not exactly in the plumb. Their overlapping is estimated to be less than the design value of 60 cm, and some seepage-prone weak zones are thus developed. The measured hydraulic gradient being equal to 12.1 and existence of seepage-prone weak zones are deemed as the main cause initiating the water leak incident. The pinhole test results highlight not only the nonplastic nature of the Kaohsiung silt but also its vulnerability to piping under large hydraulic gradients. Some bullet points that indicate what engineers should do or avoid are learned and summarised.