Sinkholes can occur naturally or be man-made.

"Sinkholes can occur naturally when earth beneath the surface is eroded, typically by water, resulting in subterranean cavities," Transport Minister Lui Tuck Yew told Parliament last year.

Non-Constituency Member of Parliament Gerald Giam had asked Mr Lui last year about excavation works for the MRT Downtown Line and the sinkholes they cause.

Mr Lui said that in the excavation of underground structures, cavities can form when water or fluvial sand leaks into the excavated area.

"If these cavities are not detected and filled up in time, they will eventually cause a sinkhole."

He spelled out steps taken to minimise sinkholes:

  • Before any major underground construction, the Land Transport Authority (LTA) investigates ground conditions and ensures that appropriate construction methods are used.
  • Instruments are installed to monitor the ground and building settlement at all times.
  • LTA monitors the condition of the roads, especially those near excavation sites or where tunnelling works are ongoing, to look out for signs of ground settlement or movement.
  • Tunnelling control parameters are strictly followed to ensure safety.
  • LTA checks for potholes, cracks and other physical defects on all roads regularly.