Sarawak’s first RCC dam
By Rintos Mail
dipetik dari Borneo Post Online
Once completed, the Bengoh Dam will store about 144.1 million cubic metres of water, hence increasing the yield of raw water for the Batu Kitang treatment plant from 484 to 2,047 mega litres per day
IN a ravine, about 56km from Kuching, an impressive engineering feat is taking shape — Sarawak’s first major roller compacted concrete (RCC) dam in the form of the Bengoh Dam.
About 62m high and 267m long, the dam, designed to remain strong and durable, is Malaysia’s second after the Kinta Dam in Perak.
With a lake surface area of about 10 sq km, it is aimed at securing Kuching’s water supply for the foreseeable future.
The water will be trapped from the Bengoh River that flows into the basin and creates a huge raw water lake, releasing the water through the 56 metres spillway downstream to feed Sungai Sarawak Kiri.
Once completed, the dam will store about 144.1 million cubic metres of water, hence increasing the yield of raw water for the Batu Kitang treatment plant from 484 to 2,047 mega litres per day (MLD).
During a recent site visit by Energy, Green Technology and Water Minister Datuk Peter Chin Fah Kui, RCC was in the spotlight as construction on the dam moved ahead.
Local-based company, Naim Holdings Berhad, is the main contractor while local consultant firm KTA (Sarawak) Sdn Bhd handles the overall design.
The project’s contract that includes clearing, excavation, foundation exploration and preparation, and related work to ready the dam construction site for RCC placement, was awarded to Sinohydro Corporation (M) Sdn Bhd.
Costing RM310 million overall, the project will help meet the water needs of greater Kuching City and Samarahan Division until at least 2030.
Australian consultant Warwick Dart, met at the site, said RCC had three key properties that make it uniquely suited for dams — economy, performance and high-speed construction.
According to him, it has the strength and durability of conventional concrete but at a cost that rivals earth or rockfill construction.
Dart, presently a consultant with KTA (Sarawak) Sdn Bhd, added that RCC had proven successful in many dams.
Before this, he was also involved in the construction of two RCC dams — one each in Australia and Perak.
thesundaypost was told that RCC protects dams from over-topping failure, erosion and even earthquakes.
It has the same ingredients as conventional concrete — cement, water, and aggregates — but RCC is much drier and can be placed quickly and easily with large volume earth-moving equipment. Generally, it is transported by dump trucks, spread by bulldozers and compacted by vibratory rollers.
The Bengoh Dam is designed with a flat, vertical upstream face and a stepped downstream face.
Its downstream steps are made with wood forms, creating steps with a height of about three metres.
Dart said RCC work on any location of the dam required 72 hours of non-stop pouring.
The constructors are now constructing the dam base of 30 to 40 metres long. The base-width is about 80 metres.
Like any other RCC dams, sections of the Bengoh Dam are built lift-by-lift in successive horizontal layers so that the downstream slope resembles a concrete staircase.
As seen at the site, the mix was delivered to the dam via a conveyor system that runs about 200 metres, carrying the mix from the plant down the hill to a ‘tripper’.
The tripper, which could be positioned at the end the conveyor’s run, may divert the RCC from the conveyor and discharge it into the working surface at the desired location.
On the downstream side of the dam, the RCC face is visible. This is said to enhance the appearance of the RCC faces and the construction team utilise so-called grout-enriched RCC to yield a smoother face.
This involves placing uncompacted RCC along the form edges, applying a neat cement grout into the RCC surface, then vibrating the grout into the RCC to enhance a narrow zone of RCC and thus yield a smooth face.
RCC is not only a relatively new product, said to have been developed in the 1980s, but RCC construction also requires new construction techniques.
Examples include mixing of a no-slump concrete, external compaction of the no-slump concrete, utilising vibratory steel drum rollers and the continuous placement of RCC so that the resulting product is a monolithic block.
The basic RCC mix consists of a graded aggregate or aggregates, cement (a pozzolan may also be included) and water.
When properly mixed and placed, it takes on the properties of conventional concrete. Placement is accomplished, utilising conventional construction equipment.
In dam construction or rehabilitation, the RCC mix is generally spread with a dozer in level lifts and compacted with a steel drum vibratory roller.
Final strength achieved by the RCC is greatly affected by density. The closer to maximum density, the greater the compressive strength. The actual mixing of the various ingredients is accomplished in a twin shaft pugmill.
These pugmills insure a well-mixed, homogeneous product through a violent mixing action in the pugmill mixing chamber.
This mixer is superior to a drum type mixer when dealing with low or no slump products.
The typical drum mixer tends to merely fold the material.
Currently, the physical development of the project is about 34.56 per cent completed.
According to Chin, the state government is also seriously looking at redesigning the dam into a three mega watt mini-hyrdro to be connected to the main grid.
This will be done in the later stage, depending on the dam’s design and performance.
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Ulasan Penerangan: Sekarang kita sudah dengar cerita tentang Empangan Bengoh, apa pula ceritanya dengan Empangan Bakun yang gah itu sekarang? Sudah lama tidak mendengar sebarang khabar berita mengenainya.
Pernah sahabat penerangan dimaklumkan oleh seorang pekerja projek Pembinaan Empangan Hidroelektrik Bakun ini, katanya empangan itu hanya akan pecah akibat gegaran kalau satu Sarawak ni dah tenggelam dulu. Hebat, maksudnya empangan inilah salah satu struktur yang paling kukuh yang duduk di atas tanah Borneo ini!
Kalau ALLAH SWT nak tukar taqdir menjadi sebaliknya, tidak mustahil Bakun boleh hancur dulu!
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