Invert Anomalies in Operational Rock Tunnels: Appearance, Causes, and Countermeasures

The prevention of tunnel service by problematic invert-related anomalies breaks with the conventional concept that a rock tunnel is durable. This study reexamines invert anomalies in rock tunnels reported in Taiwan and in the literature in the past two decades. The diverse appearances of invert anomalies can be classified into six typical patterns: deformed invert, displaced invert, cracks, water inrush, mud inrush, and overabrasion. Possible causes accounting for these invert anomalies can be recognized as swelling ground, squeezing ground, earthquake, groundwater pressure, neighboring slope movement, displaced fault zones, and abrasion by passing water. Active and passive measures applied to mitigate invert problems are investigated on the basis of generic performance. (C) 2015 American Society of Civil Engineers.