Civil Engineering Reference
In-Depth Information
Figure 21.67
Compression tests on green mortar (Wittke 2012)
Examples
In a parametric study, a tunnel was investigated with an overburden height of 50 m
and an internal diameter of 9 m that is lined with 40 cm thick concrete segments and
located in a sedimentary rock with horizontal bedding-parallel discontinuities and ver-
tical joints that strike parallel to the tunnel axis. The deformation modulus of the rock
mass was selected as E = 2000 MPa. The cohesion and the friction angle of the bed-
ding-parallel discontinuities were specified as c
B
= 0 and
φ
B
= 30°, respectively. The
shear parameters of the joints c
J
and
φ
J
and Young's modulus of the annular gap mor-
tar E
M
were varied (Wittke 2012).
Four FEM analyses were carried out using the WBI program system FEST03 (Section
10.7.1). In cases 1 to 3 the shear parameters of the joints were selected as c
J
= 0 and
φ
J
= 20° (Figs. 21.68 - 21.70). The mortar moduli in cases 1 and 2 were assumed as
E
M
= 3 MPa and E
M
= 500 MPa (Figs. 21.68 and 21.69). In case 3, at the roof and the
invert a high mortar modulus (E
M
= 500 MPa) and at the sidewalls a low mortar mod-
ulus (E
M
= 3 MPa) were assumed (Fig. 21.70).
In all three cases, the normal thrusts in the segmental lining do not differ significantly,
while the bending moments are considerably different. As can be derived from the anal-
ysis results a low modulus of the annual gap mortar generally leads to high bending
moments in the segmental ring (Figs. 21.68 - 21.70).
In case 4, the shear parameters of the joints were increased to c
J
= 100 kPa and
φ
J
= 35°, and for the mortar a low modulus of E
M
= 3 MPa was selected. As shown in
Fig. 21.71, the increase of the shear strength of the joints has a favorable effect on both
the normal thrusts and the bending moments in the segmental lining.
Search WWH ::
Custom Search