Along with the main tunnel, an Escape Tunnel with approximately the same length, 24 cross passages connecting the two tunnels every 375m and 3 underground substation caverns complete the main features of T-48 Project.
Along Tunnel T-48’s alignment, among the expected hazards scenarios as per geomechanical rockmass behavior, the water inﬂow at the excavation face was one of the most representative in practically 100% of the tunnel extension, with some locations being classiﬁed with a “high occurrence” level with possible high water pressure and volume, namely the crossing of deep gorges and nalas, as well on the last 1000m near the North Portal with expected water ingress values of > 100 l/min. Effectively, during the excavation of tunnel T-48, water ingress at the face was a constant presence, especially on the North Portal drive where during approximately 3 months the excavation progress of Main Tunnel and Escape Tunnel was strongly affected due to general and widespread water inﬂow in a good quality but fractured rockmass with measured discharges at the tunnel portal reaching 400 l/sec.
Periodic situations occurred also where a high inﬂow of water burst into the tunnel face causing limited collapses and cavities, stopping the excavation advance for additional support measures and drainage solutions. For all unexpected situations, Lombardi Engineering as the appointed Detailed Design Consultant, responsible for the entire civil and E&M design as well the work supervision at site, suggested and deﬁned the approach for the implemented solutions.