To link the Fort Canning and Bencoolen MRT stations on the upcoming Downtown Line 3, Land Transport Authority (LTA) engineers had to build tunnels just 1m above the existing North East Line (NEL) tunnel - the closest two lines have run on Singapore's rail network.
Built over nine months between 2013 and 2014, they also cross below the North-South and Circle lines, at 8m and 3m respectively.
The Fort Canning tunnel was recognised yesterday by the Institution of Engineers Singapore (IES) as one of the top 50 engineering achievements with the greatest impact on Singapore since 1965.
The feats were picked by people who voted online from a shortlist of 113 entries to an IES competition.
The winners were 28 public sector projects and 22 private sector projects.
The LTA garnered 11 awards, the most by any agency.
Five other achievements
AIR+ Smart Mask The 2013 haze led Innosparks, a unit of ST Engineering, to create a mask with a microventilator that has a mini fan to keep the user cool. Traditional masks were humid and stuffy when worn.
Breaking the Arctic Ice Asia's first icebreaking ships for the Arctic region were built in Singapore by Keppel Singmarine in 2008. They can cut through solid ice of over 1.7m thick while operating in temperatures as low as minus 45 deg C.
Infrared Fever Scanning During the 2003 Sars outbreak, the Defence Science and Technology Agency and ST Electronics produced a machine that can detect a person with fever unobstrusively. Using their knowledge of radar, electro-optics, IT, applied statistics, physics and human physiology, they adapted military thermal imagers to produce the system.
Gardens by the Bay The concrete and steel supertrees there, which are as tall as 16-storey buildings, tap solar energy to provide lighting at night.
Deep Tunnel Sewerage System This system of tunnels channels used water to advanced treatment plants by gravity for it to be reused. It makes Singapore more self-sufficient in water, and frees up prime land occupied by conventional plants.
Lim Yan Liang
LTA senior project engineer Esen Sze, who was in charge of the Fort Canning tunnel project, said: "Our job was very, very challenging as we had to make sure construction work close to these live lines was stringently controlled."
Hundreds of instruments were placed in the tunnels of the other lines, monitoring them 24 hours a day to ensure that their power lines were not affected and there was no impact on the track beds.
"Once the track bed is out of position, it can cause a derailment," said Mr Sze, adding that physical checks of the track bed were conducted between 1am and 4.30am, when no trains were running.
Prior to the tunnel, the closest distance between two lines was 4m, between the DTL and the NEL at the Little India station.
Tunnelling under Fort Canning, engineers also had to worry about boulders with diameters of between 2m and 5m, which could badly damage cutters on the tunnel boring machine. It can take up to 36 hours for the cutters to be replaced and workers who do this must prepare in a compression chamber to condition themselves for greater air pressure underground.
Other projects by LTA that were selected include the world's first Electronic Road Pricing scheme and the NEL, the world's first fully automated underground driverless heavy rail rapid transit line.
The Next Generation Nationwide Broadband Network set up by the Infocomm Development Authority to give all residential and non-residential properties here high-speed broadband access was also among the public sector projects selected.
Also recognised were the Republic's first 50-storey public housing project, the Pinnacle@Duxton, and My Waterway@Punggol, the first man-made waterway designed as a landscape feature in a housing estate, both by the Housing Board.