Warta Geologi, Vol. 46, No. 1, April 2020, pp. 17–20

Assessment of supporting system of Hulu Terengganu
hydroelectric surge chamber cavern in Malaysia

Onimisi A Jimoh, Shehu Shaib Abdulazeez, Mochamad Trisugiwo,

Hareyani Zabidi*

School of Materials and Mineral Resources Engineering,
Engineering Campus, Universiti Sains Malaysia, 14300 Nibong Tebal, Pulau
Pinang, Malaysia

* Corresponding author email address:
srhareyani.zabidi@usm.my

Abstract:
When rocks are excavated, the in-situ stress is disturbed and thereby causes a
state of instability due to the deformation caused by the creation of space in
the in-situ rocks. This research assessed the supporting system used in a surge
chamber cavern excavated for Hulu Terengganu hydroelectricity project in the
northeast of Peninsular Malaysia. The results obtained were compared with the
installed supports. Geological mapping of the excavated region was carried out to
outline the discontinuity parameters of the rock. The rock mass quality (Q),
the rock mass rating (RMR), the geological strength index (GSI) and the
uniaxial compressive strength were evaluated using standard methods and
procedures. The strength and rock mass properties were further used to classify
the rock and establish the required standard supports for the surge chamber
cavern. The wall height is approximately 40 m. It requires systematic bolting
with 7 to 11 m length of rock bolt at a maximum wall spacing of 1.5 m. The
required reinforce shotcrete falls within a thickness of 50-90 mm. The
currently installed shotcrete is within the minimum of 50 mm thickness and has
a spacing of 3.0 m along the wall which is too large for reliable safety. The
cavity of the crown is critical and to consider unforeseen geological
weaknesses in rock mass, maximum safety must be ensured by increasing the
current thickness of the shotcrete and reducing the spacing to a maximum of 1.5
m as evaluated using the rock mass properties.

Keyword:
Rock mass rating, geological strength index, deformation, shotcrete, cavern

DOI :
https://doi.org/10.7186/wg461202004

ISSN
0126–5539; e-ISSN 2682-7549