Civil Engineering Reference
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by Lamas et al. (2010). This method is based on the following two assumptions regard-
ing the in-situ stress state:
- One principal in-situ stress is vertical, the other two are horizontal.
- The principal normal stresses are zero at the ground surface and increase linearly
with depth.
As a first step an analytical or numerical rock mass model is established in which, for
example, the forming of topographically non-uniform landscapes, manmade interven-
tions such as underground excavations and so on are simulated. Then a linear equation
system is set up that relates measured and calculated stress components. This equation
system is then solved by the least square method.
The so-called “integrated stress determination method (ISDM)” was developed to in-
tegrate different types of stress data to a regional stress field (Cornet 1993, Ask 2004,
Ask 2006). This stress field is set up as a function of parameters accounting for spatial
variations. The approach of the stress field includes some simplifying assumptions as
in the case of the global stress interpretation model. Within the rock volume of interest
the stress field is considered as continuously variable and determined as the best fit to
all available data by means of an adequate mathematical algorithm.
During construction of rock engineering structures, in addition to stress measurements
displacements due to excavation are also often measured and subsequently interpret-
ed by means of numerical analyses with respect to the large-scale in-situ stress state.
This procedure has been successfully applied in practice by WBI (Wittke & Soria 1983,
Wittke 1990, Wittke 1991, Wittke et. al. 2002, Wittke et al. 2003). Two examples for this
procedure will be presented in Section 16.7.
Interpretation of measured displacements with respect to the large-scale in-situ stress
state by means of analytical and numerical analyses was also reported on by Jagsch
(1974), Plischke (1984), Sakurai & Shimizu (1986), Sakurai & Akutagawa (1994), Wiles
& Kaiser (1994a) and Wiles & Kaiser (1994b).
16.7
Case Studies
16.7.1 Underground Powerhouse Cavern
In the following example, stress and displacement measurements are interpreted with
respect to the in-situ stress state existing in the area of the underground powerhouse
cavern of the pumped storage plant Estangento-Sallente, located in the Pyrenees, which
was constructed in the early 1980s. This pumped-storage plant is equipped with four
units giving a total capacity of 406 MW. The upper reservoir is formed by the natural
lake Estangento. The lower reservoir is created by a rock fill dam. The difference in
elevation between upper and lower reservoirs is about 400 m. The underground power-
house, with a length of approx. 90 m, has a maximum height of 37.5 m and a width of
20 m (Fig. 16.19). Design and construction of the cavern will be described in Chapter
22 (Wittke & Soria 1983, Soria & Wittke 1985, Wittke 1990).
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