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Department of Geo-
science and Petroleum
Spring 2017
Stability Assessment Of
Water Tunnel Passing
Through Swelling And
Slaking Rock Mass,
Chile
Supervisor:
Krishna K. Panthi
Co-supervisor:
Thomas Schönborn
In cooperation with:
Statkraft
Silje-Elin Skrede
Background
During the development of several hydropower
projects in South America, challenging rock
behaviour has been experienced. This includes
disintegration, slaking and swelling of rock
mass, as well as weakness zones containing
swelling clay. The actual behaviour has differed
from the estimated. Studies on the properties
of the rock mass might lead to a better
understanding, which in turn results in a better
a better way to predict these challenges.
A project work carried out prior to the thesis,
involved a theoretical study on swelling and
slaking of volcanic rocks, as well as laboratory
tests on samples from a specific case from
Chile. X-ray diffraction showed swelling clay in
at least one of the samples, together with a
swelling
pressure of 1.1 MPa on intact rock disks in
oedometer. The same sample had a slake
durability of 41.4 %, which is characterized as
low. The aim of the thesis is to further assess
the rock mechanical properties of the samples,
to use in a stability assessment together with
the results from the project work. Uniaxial
compressive strength will be estimated from
the Point Load Index test, and tests will also be
conducted to determine E-modulus, Poisson’s
ratio and density. The results will be used in a
stability assessment of the tunnel the samples
are gathered from, including analytical analysis
and numerical analysis in RS2 and RS3.These
results will further be compared with each
other, and actual stability in the tunnel.
MASTER THESIS
Figure 1: Intact rock
discs prepared for
swelling pressure test in
oedometer
Figure 2: Rock pieces
prepared for slake
durability tests