Y. Spira, R. Lackner, C. Pichler, and H. Mang, “Viscoplastic material models for soil: new insight into the soil-support interaction in NATM tunnel excavations”, Arch. Mech., vol. 57, no. 2-3, pp. 209–240, May 2005, Accessed: Dec. 13, 2025. [Online]. Available: https://am.ippt.pan.pl/index.php/am/article/view/v57p209