CASE STUDY
Flood Mitigation at Admiralty Rd West
SINGAPORE, SINGAPORE
The Challenge
Climate change has brought about extreme weather events, bringing unpredictable rainfall and rising sea levels resulting in flash floods occuring around Singapore over the years. There have been several flash flooding incidents occuring along Admiralty Road west causing inconvenience to the motorist along the area.
Figure 1: Flash Flood at Tan Kah Kee bus stop area
The Solution
To prevent further occurrence of flash floods along admiralty road west, Hocklim Engineering was tasked with widening the existing box cover by building a drainage across Admiralty road west. This will help to increase the volume of water flow into the drainage system, thus alleviating the flash flooding occurrence around the area.
Utilities management
Before excavation begin, it was necessary to investigate the presence for any existing live underground services. Using the trial trench and probing with a plastic drill bit, various live services were identified underground. The live services identified were old British army fuel pipes (on the surface), Singtel cables, 66KV, HT cables, LV cables, 300mm dimeter water mains and 1800mm water main, which were found to be 1-5 meters deep underground. To ensure no damages to the live services occur during the entire project, they were protected using temporary structural steel support which was specifically designed by Hocklim Engineering's professional engineer.
Figure 2: Trees to be transplanted were tagged with bright-colored tapes for easy identification.
Figure 3: Ensuring that the tree roots were not damaged during the transplantation
Deep excavation
Due to the presence of the existing live services, the excavation process became tedious as additional protection work was needed to ensure that the live services were not damage during the excavation process. In order to do so, the setting up of ERSS (Earth Retaining Stabilising Structure) by sections parallelly aligned to support the live services and retain the surrounding soil during the deep excavation. This results in a more time consuming and labor intensive job.
Figure 4: Manual excavation to ensure cables were not damaged
Tidal water management
As Admiralty Rd West is close to the sea, the need to control the tidal water and rain water flowing to and fro through the outlet drain during the entire process was necessary.
In order to do so, Hocklim deployed, 2 automated tidal gates to control the flow of sea water. The automated tidal gate operates with a sensor that activates based on the water level. This ensures that Hocklim is able to control the water flow during the entire project, thus prolonging the working hours by creating a conducive work environment.
Figure 5: Vibration meter to measure vibration levels
Using natural energy for site power supply
Hocklim firmly believes in reducing carbon emission and protecting the environment. One example is to use solar panels to replace some of the diesel empowered generators for power onsite.
These include the CCTV system onsite, the electricity at the temporary bus stop and the automated tidal gates. The reliance on natural power allows Hocklim to be more environmental friendly while lowering its cost simultaneously.
Figure 6: Installation of U-drains before a top slab is casted to close off the drain
Traffic diversion
During the tender stage, the notional design of the traffic diversion was a six-phase diversion scheme. Hocklim optimise the six-phases into a two-phrase diversion scheme. This greatly reduces the impact to the existing traffic while improving the work continuity. Traffic diversion inconveniences the public and frequent changes to the road alignment may confuse road users etc... at a cost//
Figure 7: Motorized winch and manual hand crank installed
Lastly, this entire design solution will not be possible without the collaboration with Mr. Tan Hooi Soon of PUB. With his contribution, the design solution of the Box drain had proven effective in mitigating flash floods along Tan Kah Kee area as the overall capacity of the drain had increased by 425.12m³ to adequately deal with the excessive rain. In addition, the installation of Stoplogs is essential in managing the water flow in the Box drain.
This entire system also requires minimum manpower to operate as it can be controlled remotely via a website that streams the CCTV image in real-time ensuring quick response time to activate, making it a reliable, efficient and effective flood mitigation system.
Figure 13: Stoplog A in operation
