The Straits Times reported that the Land Transport Authority (LTA) is finding new ways to assess soil conditions before construction starts, with new underground rail lines being built below existing buildings and infrastructure.

These geophysics methods - which make use of ground vibrations or electric currents - are used when more direct means of surveying, such as drilling boreholes cannot be done. This was encountered at six locations along the northern section of the Thomson-East Coast Line (TEL), where construction moved into full swing yesterday following a ground-breaking ceremony.

Different types of ground have different densities, which produce different rebound velocities, so that is used to identify the nature of the soil, LTA said.

In 2012, houses in Watten Estate in Bukit Timah were damaged due to underground soil movements from the Downtown Line construction. Recharge wells had to be used to pump water back into the underlying soil to replace seepage caused by construction.

For the TEL, LTA said it will closely monitor the impact of construction, especially at Housing Board flats near Woodlands South station, shophouses near Springleaf station, and terrace houses near Upper Thomson station.

The TEL, which also has nine stations along the East Coast, will open in stages from 2019.