ABSTRACT
In conventional tunneling, particularly utilizing the New Austrian Tunneling Method (NATM), lattice girders and steel ribs are commonly employed as primary lining support elements with temporary character. Official guidelines stipulate the use of one lattice girder per excavation round as a temporary support measure. However, deviations from this standard, such as installing multiple lattice girders per round, have been observed in numerous global tunneling projects. This research paper aims to quantify the impact of lattice girders and steel ribs on the strength of primary support and to validate the recommended practice of using one lattice girder per excavation round. The study includes analyses to determine whether lattice girders significantly enhance the structural integrity of the primary support or merely serve as temporary aids until shotcrete and anchors are fully established. Investigation seeks to establish whether lattice girders contribute to the strength and stability of the primary support as currently recommended.
