Damages Caused by MRT Construction in Watten Estate

Mr Png Eng Huat asked the Minister for Transport (a) what additional steps are taken to assess the suitability of the surrounding areas for the construction of underground MRT lines in the wake of the Watten Estate incident; (b) what information and assistance will be given to residents living along MRT construction lines to assuage their concerns about underground tunnelling given that the new Thomson line will be entirely underground.

Page: 963

Sir, the property damage in Watten Estate resulted from ground settlement, likely due to an unexpected and rapid drawdown of groundwater during the excavation works for the Downtown Line 2. This is at the Tan Kah Kee Station site, which is more than 100 metres and more away from the Watten Estate area, across Bukit Timah Road, across the canal and across Dunearn Road.

Once LTA was alerted to the incident and had made its assessments, more recharge wells were installed to pump in water and stabilise the ground settlement. LTA has also installed additional instruments to monitor groundwater levels. Since the early days of the incident, there have been no further reports of property damage.

LTA has taken prompt action to make temporary repairs to the property damages for the residents while investigations to ascertain the actual cause of the ground settlement continue. When tunnelling work for Downtown Line 2 is completed around the end of 2013, LTA will make good the damage to properties caused by the construction.

Let me assure the House that LTA places paramount importance on safety and will take all appropriate precautions in the construction of our road and rail projects. Before LTA commences any construction works, it first undertakes a comprehensive engineering assessment to ascertain the effects of the construction work on its immediate surroundings. This includes very extensive investigations of soil profile, historical land information as well as surveys of surrounding areas. Detailed analyses are also carried out to determine the zones likely to be affected by the excavation works, and the engineering protection works required. As construction commences, LTA continues to closely monitor water seepage and ingress that may result in changes to groundwater levels. Where there are indications of problems, LTA will institute restorative measures without delay.

Mr Speaker, I thank the Minister for his comprehensive answer. I have three supplementary questions. Firstly, my concern is not just for the Watten Estate area but also other areas that surround sites where the MRT Lines are being constructed. Was LTA aware of the possibility of this water seepage? I understand that there were assessments being done but yet still the water seepage happened. Was LTA aware of the possibility that these excavation works could affect a radius beyond what the computer modelling was predicting? Was this factored into the preparations? Secondly, I understand from the Minister that there were some sensors placed to monitor the level of groundwater. Were these sensors not able to detect movements in the groundwater before the cracks occurred, or did LTA only respond when the cracks were reported?

Page: 964

On whether LTA is aware of the possibility of groundwater seepage, certainly that is something that they are very mindful of. There were two previous occasions that I recall when buildings were similarly affected by previous construction works. One was in Bussorah Street during the construction of the Circle Line. The more recent one was around the city area – Cross Street, I believe – during the construction of Downtown Line 1.

What they do prior to construction is to do a comprehensive survey of the ground and assess what they think would be the likely impact area. If there are buildings within the likely impact zone, then they would take necessary actions to strengthen the grounds or to protect the buildings. They would also place sensors to try and give them as much early warning as possible of impending soil movements. We would appreciate that the geology in Singapore is actually very diverse and complicated. Along the same Downtown Line, you will run into segments where you have very, very hard rock, huge boulders. In fact, that takes massive amounts of work and explosives in order to remove. On the same stretch, you would run into alluvial and marine clay. It differs from station to station and each stretch of the tunnel. But LTA strives to be as comprehensive as possible.

On the sensors, if I were to move a little into the history of this, we first had some isolated feedback on cracks back in June 2011 from the area. In June 2011, we had not even started excavation works because the bulk excavation works only started in December 2011. As a precaution, LTA extended the surveys that were placed over onto the Watten Estate Park site. Those sensors were installed in early 2012. In late August, early September of 2012, LTA noticed that the sensors were telling them of some movements of the soil. At the same time, LTA was also alerted by some residents that they were experiencing cracks in their houses. So that is really the timeline for what we saw in the Watten Estate area. And thereafter, LTA went in, walked with the house owners as well as the contractors to take precautionary measures, both to deal with the defects that were observed as well as to take additional precautions around the Tan Kah Kee site.

Page: 965

[Gesturing with his hands] This is Watten Estate, Minister, and this is Tan Kah Kee Station and this is Bukit Timah Road and everything behind Bukit Timah Road. My ward is everything behind Bukit Timah Road. There is Hwa Chong Institution and behind Hwa Chong, condominiums and landed housing. And therefore I would request that LTA also prioritise the concerns and be proactive in preventive measures of cracks happening on that side.

I thank the Member for bringing up this point. Indeed, LTA is very mindful of the possible impact on Hwa Chong Institution as well as the estate on the Bukit Timah side. In fact, that was actually of a greater concern compared to my side of Bukit Timah on the Dunearn Road side. LTA will try to be as comprehensive as possible, both in terms of the site surveys and in terms of the instrumentation. But we would appreciate that given the very diverse geology and also we do not want to over-do things, that it is sometimes not possible to foresee every possible eventuality. After all, I think perfect foresight is as rare as 20:20 hindsight is common. So, LTA will continue to watch the area very closely. If there is feedback from the residents, they will take action to investigate it as soon as possible and, if necessary, take step to do the rectification works.

Page: 965