TBM Tunneling - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 710

tion confined lateral strain was assumed. After “stressless installation” of the concrete
(Section 10.5.2) the pre-stressing forces were removed. Thus, segments are loaded by
so-called “restoring forces”.
The 40 cm thick lining segments were designed for a concrete quality of C45/55 and
for a steel FeB44K. Four different types of segments with regard to reinforcement
were produced to cover the widely varying ground conditions (Table 21.1). Type I has
a minimum reinforcement of a s = 6 cm2/m in the circumferential direction resulting in
a quantity of reinforcement of approx. 130 kg/m3. This type of segment was installed
over 84% of the tunnel length. For higher overburden and/or poorer ground conditions
the stronger reinforced segment types II, III and IV needed to be installed (Table 21.1,
Fig. 21.52).

Table 21.1 Reinforcement of segment types (Wittke et al. 2006)

Type Reinforcement (steel FeB44K) Proportion of total

tunnel length [%]

bending
[cm²/m]

shear
[cm²/m]

quantity
[kg/m³]

I - 134 84

6 (a s,min )

II 16.6 - 189 5

III 45.3 - 354 10

IV 45.3 15.7 361 1

The detailed modeling of segmental rings, including segments and longitudinal joints,
with finite elements allows the computation of continuous distributions of stresses and
stress resultants in the segmental lining. As an example, Fig. 21.53 shows the principal
normal stresses in the area of a longitudinal joint. In the area of the contact plane large
compressive stresses and transverse tensile stresses occur. Figure 21.54 shows the radial
stress components in selected sections calculated in the same analysis.
To determine the tensile splitting forces due to the jacking forces applied to the circum-
ferential joints, three-dimensional analyses were carried out for an individual segment.
The FE-mesh is represented in Fig. 21.55. At the front face, the loads due to the jacking
forces were applied. At the back side, the hardboard plates for load transmission to the
adjacent ring were simulated by supports (Fig. 21.56).

In Figs. 10.35 and 10.36 (Section 10.5.5) the principal normal stresses in the mid area
of the segment are represented in a developed view. Between the jack shoes, transverse
tensile stresses occur due to the load distribution from the jacks to the hardboard plates
at the back side. These tensile stresses needed to be covered by a corresponding rein-
forcement.