INGENIEUR
MANAGING CHANGED CONDITIONS
DURING CONSTRUCTION
The original tender design was based on the
premise that the ridge must be retained at least
EL 46m so that the original reservoir storage can
be retained. As the Penang State Government
agreed to lower the existing reservoir to EL 34m
the ridge was cut down to EL 35m. This allowed a
balancing channel to be constructed to connect
the left and right reservoir. This meant a single
draw-off works was possible. The draw-off tower at
the right valley could be omitted and replaced with
a low level draw-off. Other works such as access
bridge to the draw-off tower, extension of existing
culvert to accommodate heightening of existing
dam could be omitted.
The modification to the design described
above resulted in saving of over RM50 million
from omission of permanent works and import
of earthfill materials. Besides saving in cost and
time, it also resolved the problem of shortage
of construction materials, and mitigated the
risk of construction and potential social and
environmental problems.
CHANGE OF DESIGN
Revised Design of Dam Heightening
The tender design for raising the height of
the existing dam embankment from crest
level EL45.72m to EL56.6 m was confined to
downstream slope (see Figure 14). A new cut
off system consisted of a clay core at the raised
portion of the dam embankment, a concrete cutoff wall through the downstream slope of existing
dam terminating at bed rock and a grout curtain
below the concrete wall.
With the omission of draw-off tower and access
bridge at the upstream slope, it was feasible to
raise the dam by filling on both upstream and
downstream slopes of the existing dam. The clay
core of the raised dam was inclined and integrated
with the clay core of the existing dam (see Figure
15). The revised design educed the extent of
settlement. The chimney filter and internal
drainage system of the existing dam was retained.
6
14
VOL
- MARCH 2016
VOL65
55JANUARY
JUNE 2013
The revised design resulted in moving the toe
of the raised dam further away from Sg. Lembu
Road, mitigating the problem of interference with
the public road during construction.
Revised Layout of Spillway
The layout plan of the tender design of the spillway
was revised. The spillway chute was curved in order
to avoid the filled embankment of raised dam. It
was hydraulically not efficient and its construction
more complicated. The revised dam raising design
resulted in more space available at the right
abutment for a straight spillway chute which was
hydraulically more efficient (see Figure 16).
CONTRACTUAL IMPLICATIONS
RELATED TO DESIGN CHANGE
The revision of design during the construction
stage resulted in contractual claims by the
contractor on the basis of changed conditions.
However, the impact on the contract was
far outweighed by the significant saving in
construction costs and other benefits related to
technical and environmental factors. The option
of do nothing would forego the opportunity to add
value to the project.
Satisfactory execution of this major dam
project required the consultant and implementing
agency to be able to manage situations without
causing delay and cost over-run.
CONCLUDING REMARKS
Completing such a major civil engineering project
in a populated area was not an easy task. The
successful completion of the Stage 1 dam
expansion project in July 2015 demonstrates that
through the co-operation and collective effort of
the project developer, land owner, consultants and
contractors, many challenges involving technical
problems and contractual issues can be managed
and brought to completion in relatively short period
of four years. The spirit of partnership along with
the willingness to deliver are the keys to responding
to changing conditions which are inevitable in large
dam projects and water supply infrastructure.