Alhamdulillah, with the help of Dr. Rini Asnida Abdullah and the Tunnel Underground Space Technical Division of IEM (Ir. Chong Chi Koong, Ir.Neo and Mrs. Zainun), the Tunnel Engineering class under the Department of Geotechnics and Transportation, School of Civil Engineering, had successfully organised a technical site visit to a pipe-roofing tunneling at Sungai Bunus Pump
Gate Station on 28th September 2019. In total, sixteen students participated in this technical site visit (8 from Geotechnical Master of UTM KL and 8 from UTM JB).
The participants boarded a school van and departed from M50, School of Civil Engineering at 4:00am and arrived at the project site office at 8.30 am. After having settled down at the project conference cabin, an overview of the project was delivered by the owner of Project, Ir Marina Abdul Karim, Senior Assistant Director, Department of Irrigation and Drainage, Federal Territory of Kuala Lumpur; the consultant team – En. Azman Bin Abu Bakar and Dr. Esam Ahmad from Perunding Azman, Ooi & Rao Sdn Bhd.
Ir. Marina explained that this project is implemented by the Department of Irrigation and Drainage (DID), Federal Territory Kuala Lumpur as part of the Rancangan Tebatan Banjir Sungai Bunus to mitigate the frequent flooding issues in the Sungai Bunus catchment area. The old existing catchment of Sg.Bunus (known as lencongan lama) built in 1968 could not bear the current capacity. For instance, two severe flooding events had occurred in the Jalan Tun Razak area between the years 2011 and 2012. More details of DID decision on this development can be read at http://www.myiem.org.my/download/downloadlink.aspx?fn=17520_3118%20-%20Jurutera%20online.pdf&id=17520.
In addition, Mr. Azman said that as the respective area was already packed with buildings, there was very little space left to create retention ponds and detention ponds. Therefore, in order to overcome this lack-of-space issue, DID had decided on a series of on-line and off-line flood mitigation ponds totaling 8 in various parts of the 7 km long Sungai Bunus catchment area stretching from Setapak Jaya Pond, Air Leleh Pond, Polapol, Kg. Boyan Pond, Sri Rampai, Air Panas area, Titiwangsa Air Panas, Kg. Baru area, and so forth, consisting of a total of 17 km length of 3 distributaries – Sungai Peras, Sungai Peran and Sungai Bunus. However, an occurrence of any one severe storm event in Kuala Lumpur would give rise to widespread flooding as the current river drainage system would not be able to cater for a massive volume of rainwater. En. Azman also touched on the high cost in land acquisitions alone without building the infrastructures. Therefore, DID needed to look for alternatives, such as available areas at both AKLEH Highway and DBKL reserves. It was decided that another diversion, which is skewed with two physical modelings using InfoWorks software was done for stilling basin and pump gate and for addressing two issues – one at Jalan Tun Razak and the other on “punching” through 2 successive Reinforced Earth (RE) walls which formed a road ramp to the AKLEH Highway. In fact, two critical areas were encountered, i.e. at Jalan Raja Muda Abdul Aziz and at the RE wall road ramp next to Sungai Klang.
Dr Esam Ahmads Abdul Rahman ALFaez, the Geotechnical Designer and Supervising Engineer from the Consultant then continued the presentation with details sharing on maintaining the stability of the RE walls during the pipe-roofing construction. For instance, this is done by doing both horizontal and vertical grouting using double-packer grouts and then tying of both RE walls. Once these were done, the 9 m of pipe-roofing were installed via pipe jacking. Finally, the space within the pipe-roofing could be mined to form a tunnel. During the construction stage, high water-table was encountered and this was overcome by installing well points system to keep the area dry. Besides, a flood wall was also in place to control flooding. Videos were played showing the construction process of horizontal grouting reinforcement and pipe roof installation. He explained the pipe-roofing tunneling system through a retaining earth (RE) wall road ramp is the first of its kind in the world that was designed and was constructed to form the opening. He added that an assembly of temporary 600 mm diameter mild steel pipes were installed contiguously at two opposing sides and at the top by hydraulic jacking or micro tunneling; thus forming a rectangular pipe-roofing tunnel. The completed pipe-roofing tunnel is to house a cast-in-situ twin box culvert which acts as a vital connection between Sungai Bunus and Sungai Klang, acting as a control-gate structure that hoists force main drainage pumping system that lifts low water level from Sungai Bunus to high water level of Sungai Klang. Dr Esam further elaborated that it is of vital importance to further enhance the stability of the RE walls prior to the construction of the opening. As such, certain measures or standard operational procedures have been adopted as follows:
1. Prior to the advancing steel pipes, a Cement-Bentonite mixture slurry would be grouted into the granular materials between the RE walls of the ramp to solidify it as well as to control the loss of granular materials during the pipe jacking operation;
2. Permeation grout is injected below the RE wall strip foundations to enhance its bearing capacity; and
3. Steel tie-rods at 1.2m spacing are introduced in a triangular pattern which is inserted and tightened horizontally to ensemble and sandwich both faces of the RE walls to enhance the ramp stability against the pipe jacking forces, and both the RE wall faces are then covered with reinforced concrete gunite.
The above measures do not only serve to enhance the stability of the RE walls but also serve to limit ground movements during the pipe jacking operation. This is so that settlements of both overlying and road pavement, as well as the movement of the RE walls, are minimised and maintained within acceptable limits. Otherwise, this would cause subsidence of the highway above and disrupting the live traffic. And for that purpose, two types of monitoring systems are implemented, i.e. Automatic Total Station (ATS) and Terrestrial Laser Scanning (TLS) which have been counter checked by precise manual levelling monitoring survey. Dr Esam also mentioned that digital cameras were also fixed to monitor the movements on both faces of the RE walls as well as the highway pavement daily, and so far, zero and very small movements within limits were recorded.
On an aspect unrelated to the purpose of this site visit, Dr Esam stressed on never to design and construct RE walls next to a river. This is because RE walls would contain lots of fine materials within them that would easily be washed away with the fluctuating river water levels and giving rise to a lot of problems. This is certainly ‘food for thought’ for engineers who may be required to design RE wall at some point in their careers. He also mentioned not to fully trust any data results coming from the laboratory but to investigate oneself using available tools and systems with the help of the contractor at the site.
During the technical visit to the pipe-roofing site, students exchanged questions and answers with the project team. After the site visit, the participants returned to the project conference cabin for some light refreshments courtesy of the project team. After that, the session chairman, Ir. Chong Chi Koong (TUSTD, IEM) proposed a few words of thanks and appreciation to the project team for having hosted our IEM members to this very interesting technical visit. The technical visit was concluded with a presentation of souvenirs to Ir Marina and En. Azman as a token of appreciation. The participants then boarded the school van from the site and arrived at the School of Civil Engineering at about 7 pm.
A lot of new exposure was gained from this visit, especially knowing about tunnel technology in Kuala Lumpur’s drainage system. Thank you to Ir. Marina, JPS team, Ir.Azman and Dr.Esam, and also the contractor team who shared with us the knowledge and experience they obtained when attending this project.
Things to ponder;
- is technology reliable/ manual workmanship much better? or technology needs to be improved to achieve a win-win situation in constructing complex job?
- RE – not a choice if to build beside river basin!
- crack your mind to pass the obstacle – create novelty in construction solution
- share more, get more!
Last but not least, thank you Abg Burn for driving us a long way to KL. This trip will not succeed without a driver you know! (and of course big thanks to our beloved Chair of SKA and Associate Chair of Academic and Student Affairs for letting us go and support us for this trip).
Dr.Siti Norafida binti Jusoh
Senior Lecturer of School of Civil Engineering