Civil Engineering Reference
In-Depth Information
The excavation of the cavern was carried out stepwise in benches. The horizontal wall
displacements due to the excavation of the cavern represented in Fig. 16.24 were meas-
ured using extensometers and convergence measurement devices described in Sections
17.4.1 and 17.5, respectively. These displacements were back analyzed using the two-di-
mensional computation section mentioned above. The best agreement between meas-
ured and calculated displacements was achieved assuming a rock mass modulus of
E = 12,000 MPa, friction angles of
φ
D3
= 40° and
φ
D3'
= 50° and a maximum hori-
zontal tectonic stress of
Δσ
H
= 9 MPa. With the extensometers only a part of the total
displacement could be measured since they measure the displacements in relation to
reference points that are anchored 25 - 30 m behind the cavern wall within the rock
mass and thus are not fixed points (Fig. 16.24).
Figure 16.24
Measured and calculated horizontal wall displacements due to excavation
of the cavern (Soria & Wittke 1985)
This example shows that the in-situ stress state can be of great importance for the stabil-
ity of a large underground opening. The interpretation of stress measurements carried
out before construction and displacement measurements conducted during excavation
by means of numerical analyses allowed a realistic assessment of the large-scale in-situ
stress state and the rock mechanical parameters in the area of the cavern, which finally
has led to a safe and economic design and construction (Chapter 22).
16.7.2 Construction Pit
The 220 m long, 20 - 30 m wide and ca. 25 m deep construction pit for the Station Uni-
versity which is part of the urban railway Stuttgart (Fig. 16.25) was also constructed in
the early 1980s. It is mainly located in claystone with single sandy limestone layers of
the Black Jurassic (Lias
α
). Underneath the Lias
α
, the Rhaetian, which is also com-
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