For the excavation of a pair of parallel tubes of the longest railway tunnels in the Czech Republic (4150 m), the S-799 boring machine named "Victoria" was used. Its diameter is 9.9 m, total length 115 m and total weight of about 1850 t.A steel starter frame is used to support the boring machine in the first stages of boring. Its shape is best suited to follow the shape of the circular ring, which is adjacent to the frame from the front. Hydraulics jacks are pressed against the ring when the boring machine is driven, generating a total horizontal force of 3000 kN.
The frame is designed as a steel superstructure consisting of two columns, two skew struts, a horizontal beam and diagonals. The columns are anchored to the base blocks in the foot, and are supported by skewstruts filled with concrete at the top. The top of the columnsis connected by a horizontal beam. The horizontal beam and columnsare further connected by diagonals.All cross-sections are designed as closed welded boxes.Our company has developed an initial static and geometrical variant study, detailed designdocumentation,3D model of the structureand shopdrawings.
