BACKGROUND

The Langat 2 Water Supply Scheme is being implemented by Pengurusan Aset Air Berhad (PAAB), a Government-owned company under the Ministry of Finance Incorporated. The scheme is to overcome the current water shortages in the State of Selangor and Wilayah Persekutuan, Kuala Lumpur.  Package 10, which is part of the scheme under Phase 1, encompasses the laying of a single length of 2500mm dia. mild steel concrete-lined (MSCL) pipeline from the proposed Bukit Enggang balancing reservoir to Sungai Besi Expressway covering a total length of 14 km. The route of the pipeline alignment would pass through a proposed Sungai Besi tunnel of approximately 527m long which is being constructed. The tunnel will cross a hill located in between Taman Desa Cheras and Sungai Besi Army Camp from east to west. It is to note that the surrounding areas of the proposed tunnel are under rapid development. Rock is exposed at the hilltop as a result of earlier uncontrolled earthworks.


TUNNEL SIZE & SECTION

In order to house a twin bulk distribution pipelines, a tunnel with horizontal invert would be most preferable, and hence a modified horseshoe with vertical legs or D-shaped tunnel of 3770mm radius was adopted. The tunnel was sized for housing the twin pipelines for both Phase 1 and Phase 2 of the Langat 2 Water Supply Scheme and space allowance was adequately provided for pipelaying works as well as for future maintenance of the completed twin pipelines. A typical diagrammatical cross-section of the tunnel (Figure 1) is as shown below.


TUNNEL CONSTRUCTION

The excavation for the tunnel is being carried out by ‘drill & blast’ method. This is further classified into bench-cut method for soil section and full-face method for rock section.

The tunnel portal support consisting of forepole umbrella as pre-lining support techniques used in soil section for stabilising roof and carrying boundary formation on roof itself then follow by installation of the steel ribs and friction bolts. Q-system, which is an empirical method, is used for classification of the rock mass and thereby, the evaluation of support requirements.

Generally, the primary tunnel support for soil section comprises of steel ribs, friction bolts and 300mm thick fibre reinforced shortcrete. Whilst that for rock section, it comprises of rock dowels and 100mm thick fibre reinforced shortcrete.

Drainage holes are provided at specific intervals to release any built-up pore water pressure surrounding the tunnel.


SAFETY REMINDER:

Participants shall be well equipped with their own PPE equipment, i.e. safety helmet, high visibility safety vest and safety boots in order to be allowed access into the site.


NOTE:
• The visit is strictly limited to 30 participants registered on a first-come, first-served basis.
• Participants must be physically and mentally fit as stated in the requirements of
   ‘Industrial Code of Practice for Safe Working in a Confined Space (2010)’.
• Please observe the ‘NO Photography Allowed’ policy at the tunnel construction site.