Technical Review of the Lined Rock Cavern Concept and Design ...

cracks have developed despite a tangential strain by
far exceeding 0.02% (0.1% strain measured).
There are 10 special joint-meters (0.25 m long
extenso meters) installed in Room 3 in the concrete
lining above definite joints in the rock surface. The
largest deformation measured is 0.79 mm at the
maximum pressure of 28 rvIPa. The deformations
recorded in all the joint-meters are shown in Figure
13. Both opening and closure of rock joints have
occun-ed.
1,0
e ,§. 0,5
.§
~
.g
~ 0,0
~,5
0 5 10 15
~ (MPa)
1 '/
20 25 30
Figure 13. Rock joint movements in Room 3.
4.3 Steel lining behaviour
As the project proceeded, it gradually became easier
to measure the strain in the lining of Room 2 due to
the installation of six micro-extensometers in all.
These sensors continuously measure the strain in the
steel lining over a measured length of 150 mm.
Figure 14 shows the strains in the lining during
Phase 4 in the micro-extensometer showing the
largest strain.
15 20 25 30 35 40 45 50 55
Pressure (MPa)
Figure 14. Strains in the steel lining in Room 2
during Phase 4 in the micro-extensometer showing
the largest strain.
The average maximum strain in the steel lining is
0.45%, thus exceeding the yield point of the steel
(0.17%). Locally, much higher strains (up to 1.1%)
have been measured due to local deformations in
A-21
connection with crack zones in the concrete. The
resulting pennanent strains in the steel lining amount
to 0.5%.
Samples from the steel have been subjected to
laboratory analysis. This metallurgic analysis implies
that the structure of ,ilie steel has not been affected
by the high pressures and that the properties of the
steel after the loadings are unchanged in relation to
the original properties.
4.4 Total behaviour
The deformations in the structure as a whole (rockconcrete-steel)
have been measured with the aid of
convergence lines. An example of diameter changes
in Room 2 during Phase 4 is shown in Figure 15.
0 5 10 15 20 25 30 35 40 45 50 55
Pressure (MPa)
Figure 15. Diameter changes in Room 2 during
Phase 4.
The total deformations at 25 MPa (expected
maximum pressure in a commercial storage plant),
and the distn"bution of the defonnations have been
SllmmSirised in Table 3. The rock mass contn"butes
50% of the total radial deformations. The remaining
part is related to defonnations in the concrete lining
and its transition zones. Local rock deformations
play an important role with regard to the total
behaviour in the pilot scale, causing a variation of
25%. The total radial deformation implies an
average tangential strain in the steel lining of 0.18%.
Table 3. Size and distnoution of radial deformation
at 25 MPa in pilot scale (diameter 4.4 m).