Inspections on slopes may be more frequent during intense wet weather

The landslide at the construction site for Clementi NorthArc Build-to-Order (BTO) flats as seen on Sept 6, 2022. ST PHOTO: KEVIN LIM
This comes in the wake of the landslide at the Clementi NorthArc Build-To-Order construction site on Sept 2, 2022. PHOTO: ST FILE

SINGAPORE - Local agencies may conduct inspections on slopes more frequently, such as on a weekly or monthly basis, during periods of intense wet weather.

This comes in the wake of the landslide at the Clementi NorthArc Build-To-Order construction site on Sept 2, caused by the sudden collapse of a slope due to changes in soil strength, also known as slope failure.

While the cause of the incident is being investigated, such soil movements may be triggered by various factors, such as heavy and prolonged rainfall, additional loads on the slope, or changes to the slope profile due to construction work, said Minister for National Development Desmond Lee in a written parliamentary response on Monday.

"Agencies that manage public land carry out regular inspections on slopes that may pose a risk to public safety, and implement appropriate mitigation measures to stabilise the slopes as needed," he added.

In addition, the Building and Construction Authority (BCA) requires all slopes that are formed or modified by building works to be assessed for risk of failure by a qualified person (QP) before construction commences.

The QP is required to recommend slope protection measures to be put in place, such as earth retaining walls and stabilising structures, to ensure the slope remains stable under adverse weather conditions, including extreme rainfall.

The QP is also required to recommend measures to monitor the condition of the slope while works are ongoing.

"The frequency of monitoring may vary depending on the complexity of the works. For example, slopes may be monitored twice a week for relatively shallow excavation works, and daily for works in close proximity to other buildings," said Mr Lee.

As a precautionary measure following the landslide on Sept 2, BCA has reminded QPs and builders to inspect slopes on or adjacent to construction sites, and to take additional measures to ensure these slopes remain stable, as needed.

BCA will conduct checks to ascertain that project parties have taken these measures.

The agency will also review the cause of the recent slope failure incident after the investigations are completed, and assess if additional measures are required to ensure the safety of slopes on or near construction sites.

Mr Lee noted that an average of four landslide incidents were reported to BCA per year between 2017 and 2019, and 21 per year in 2020 and 2021.

"These were all relatively minor cases involving the movement of shallow layers of soil, and did not cause significant damage to infrastructure." he said.

"Higher-than-normal rainfall was recorded in 2020 and 2021, which could be one factor that contributed to the higher number of incidents in these two years."

As at end-September 2022, only one landslide incident - the one at Clementi - has been reported to BCA.

Mr Lee's response was to a question posed by Ms He Ting Ru (Sengkang GRC).

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