LATTICE GIRDERS FULFILL IMPORTANT FUNCTIONS IN TUNNEL CONSTRUCTION
Lattice Girders have been developed for the special demands of tunnel construction. The Lattice system has rigorously tested and successfully installed in many tunnel projects throughout the world.
Contrary to standard rolled steel sections and regardless of shape, the Lattice system, in conjunction with shotcrete is totally surronded by concrete forming a complete homogeneous composite structure with no unconsolidated areas, voids or fissures visible. The overall result in a tunnel lining that significantly reduces ground settlement and prevents the ingress of water.
REINFORCING ELEMENT OF THE SHOTCRETE LINING
Due to the total integration with the shotcrete spray, the Lattice Girders are completely encased in concrete and form a complete composite reliable structure. The quality of the bond between the shotcrete and the Lattice Girders is determined essentially by the mechanical properties of the shotcrete (compressive and tensile strength) and the geometry of the Lattice Girders. This quality is essential for the tunnel lining to achieve its designed deflection performance.
DRILLING SYSTEMS FABRICATION
ADVANTAGES OF LATTICE GIRDERS
LATTICE GIRDERS/ 3 BARS
With spaced diagonals, 3 bars are assembled to form a girder. The single bar can be located against the ground or towards the inside of the tunnel, fitting a specified design geometry. The spaced stiffening elements reduce the local buckling length of the bars, assure a high normal and bending moment resistance and secures a transfer of lateral forces in the lining before the shotcrete has reached its design strength.
LATTICE GIRDERS/ 4 BARS
With spaced diagonals, 4 bars are assembled to form a girder. Fabrication of the girder to the design geometry is possible. The spaced stiffening elements reduce the local buckling length of the bars and assure a high normal and bending moment resistance and a secure transfer of lateral forces in the lining before the shotcrete has reached its design strength.
The 4 bar Girders are also used as longitudinal wall plates for heading and bench advances. They serve as bases and fixed points for the height and sides of the arch assembly. At the same time, they can be considered as a statically effective reinforcing of the base beam. The butt connection is rigid in bending and allows easy assembly. The arch spacing is variable.