Civil Engineering Reference
In-Depth Information
results show that the wall displacements due to excavation are mainly influenced by
Δσ
H
and the modulus E
1
for horizontal loading of the Lias
. Figure 16.32 shows the
horizontal wall displacement at the level of the berm as a function of
α
Δσ
H
and E
1
. Ac-
cordingly, the measured wall displacements of 45 to 60 mm (Figs. 16.29 and 16.30) can
be reproduced by increased horizontal stresses in the order of 1 - 2 MPa and E
1
moduli
ranging from 1250 to 3500 MPa.
Experience gained from other tunnel projects carried out in the area of Stuttgart re-
vealed E
1
values of only 1000 - 2000 MPa (Section 20.3). It was also found that the
magnitude of
Δσ
H
is dependent on the topography and on the degree of weathering and
thus on the water content w of the rock. In Fig. 16.33, this result is presented for several
tunnels excavated in the Stuttgart area (Wittke et al. 2003). A reasonable correlation
between
Δσ
H
values can be
made for the tunnels planned for the project Stuttgart 21 (Fig. 16.33).
Δσ
H
and w could be found. On this basis an estimate for
Figure 16.33
Horizontal in-situ stress versus water content, Lias
α
(Wittke et al. 2003)
16.8
The World Stress Map Project - Results of Stress Measurements
The compilation of worldwide stress data known as the “world stress map project”
was initiated by Zoback et al. (1989). The first release of the world stress map (WSM)
database was completed in 1992 (Zoback 1992). Meanwhile, in the open-access online
database WSM, administered by the German Research Center for Geosciences (GFZ)
in Potsdam, the results of stress measurements carried out according to a wide varie-
ty of measurement techniques such as stress relief methods and hydraulic fracturing
(Sections 16.2 and 16.5) as well as measurements of seismic events, the results of bore-
hole breakout analysis and the interpretation of drilling-induced fractures are brought
together (Heidbach et al. 2008). The WSM database contains stress maps of subareas
of continents in which the location of measuring points, measuring method, quality of
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