Monday December 31, 2012
High-risk walls to be checked
Reports by FARIK ZOLKEPLI, BAVANI. M, YUEN MEIKENG, NICHOLAS CHENG, RAHIMY RAHIM, M. KUMAR and STEVEN CHIEW
Photos by M. AZHAR ARIF, CHAN TAK KONG, FAIHAN GHANI, SHAHRUL FAZRY and ROHAIZAT DARUS
KUALA LUMPUR: With questions being raised on the stability of shotcrete retaining walls in the country, the authorities are scrambling to ensure that safety is given utmost priority.
In the aftermath of the shocking wall collapse in the posh Bukit Setiawangsa area here on Friday night, Kuala Lumpur City Hall (DBKL) will go in search of all such structures to draw up a hazard map.
The Public Works Department (PWD), on the directive of the Government, has formed a special task force to monitor hillslope developments nationwide.
As the uncertainty lingers, experts continued to explain the various technicalities and issues involved with shotcrete walls.
Sensitive land development specialist Dr Tew Kia Hui said it was all right to build such structures along highways where there was no topload on the soil.
He said such walls were put up to control erosion on slopes and built with a mixture of sand, cement and gravel with water added on the point of application.
“However, such walls cannot be applied for slopes that are too steep or exceeding 45° and land which has load such as buildings on top of it,” he told The Star.
Dr Tew proposed that existing hillslope projects that had applied the shotcrete wall should have confirmatory soil investigations conducted to ascertain if there were voids underneath the slopes to prevent landslides.
Universiti Kebangsaan Malaysia geology lecturer Assoc Prof Dr Tajul Anuar Jamaluddin said the soil holding the retaining wall at Bukit Setiawangsa remained unstable and a “larger failure” was inevitable if the rainy spell persisted.
On the possible causes for the wall to crack, he said there were many factors as the shotcrete wall was built with “obsolete technology”.
“I found that the wall's weepholes, which were to act as drainage to allow water to seep out, were clogged with sediment,” he said, adding that groundwater pressure built up from within the shotcrete wall and caused it to give way.
Dr Tajul, who visited the site yesterday morning, said there was also a lack of long horizontal drains installed in the shotcrete wall to allow water collected deep in the hill to flow out.
He said he found large volumes of water flowing out from the wall's ground-anchor, which holds the shotcrete together.
Penang hillside geo-technical advisory panel chairman Prof Dr Gue See Sew said the wall on Bukit Setiawangsa was not a shotcrete wall but an anchored slope as it was a cut slope, strengthened by anchors.
“There is a need to study the site in depth to determine what caused the landslide,” he said.
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