Structural design verifications, structural analysis of tunnels - Tunnel Engineering: Basics and Additional Services for Design and Construction - page 110

The basis of the iteration procedure is a calculation section, which moves in the direction
of advance. The external dimensions of the calculation section are selected so that the
stresses and displacements at the vertical boundaries do not significantly change due to
the displacement of the face by one round length. The required length of the calculation
section along the tunnel is shorter compared to the length necessary with the step-by-step
technique, which is selected according to the number of successive construction states
in the advance direction among other factors. This leads to a smaller number of element
slices for the same discretisation in the plane, and thus considerably reduces the number
of elements required in comparison to the step-by-step technique.
Figure 3-12 Simulation
of a tunnel advance using
the step-by-step technique
[186].
The basic approach of this calculation procedure is illustrated in Fig. 3-13 using the ex-
ample of the same idealised top heading advance already used in the section above. For
the following explanation, the simplifying assumption is made that the slice thickness, as
shown in Fig. 3-13, is equal to the round length and remains constant in the calculation
section.