A section of Upper Changi Road East caved in on Thursday morning causing a tipper truck to collapse into the road. The accident happened about 50m away from a construction site for the upcoming Downtown Line 3. We look at some recent cases of sinkholes which had appeared in different parts of Singapore, and what could have caused the cave-ins.
1. Keppel Road, Jan 30, 2013
What: A sinkhole appeared near a junction along Keppel Road towards Ayer Rajah Expressway during the morning rush-hour traffic. A driver, who thought it was a puddle, drove his car into it. He estimated the hole to be around 2m wide and 0.5m deep.
Why: The sinkhole was possibly caused by a pipe leak.
2. Clementi Road, March 5, 2013
What: A sinkhole 2m wide appeared in the centre lane of Clementi Road towards West Coast Road, with one motorcyclist claiming that he fell into it and suffered minor injuries.
Why: No reasons were given by the authorities. Experts say sinkholes occur when there is a loss of ground and the soil underneath the hole has disappeared. They can be caused by broken or leaking pipes and excavation works. But in this case, there were no nearby excavation works or water pipe leakages near the affected area.
3. Clementi, March 8, 2013
What: The same sinkhole on Clementi Road, which was filled just days earlier, reappeared. No one was injured.
Why: Geotechnical engineers suggested that acidic water from underground streams and rivers could have dissolved rocks in the ground, causing part of the road above to sink.
Sinkholes can occur suddenly without warning as the dissolution of the rocks may take place over a long period.
4. Woodlands Road, March 16, 2013
What: A portion of Woodlands Road caved in at about 8pm, resulting in a hole which appeared to be as wide as one lane. Traffic on both lanes of the road was blocked. The affected area appeared next to where construction work for Downtown Line 2 was being carried out by a Land Transport Authority (LTA) contractor.
Why: The massive sinkhole was caused by excavation works for the Downtown Line 2. The construction destabilised the soil, which ruptured an underground water pipe, said the LTA.
The soil movement and pipe's rupture then weakened the ground under the road, causing the sinkhole to open up. Mr Chong Kee Sen, vice-president of the Institution of Engineers Singapore, had told The Straits Times then that a mixture of soft soil and hard rock underneath posed a challenge, as Singapore continued to dig underground to build rail lines and lay pipes.
Boring through soft soil could weaken and move the soil, which may cause the road to sink when it is heavily used.
5. Commonwealth Avenue West, Dec 23, 2013
What: A section of road on Commonwealth Avenue West collapsed in the morning while workers were laying underground electricity cables. The cave-in appeared on the stretch after Dover MRT station and seemed to be as wide as one of the road's three 2m lanes. No one was injured.
Why: Heavy rain that day could have resulted in soil getting waterlogged.
What could have caused sinkholes to appear: