PUTRAJAYA: The Public Works Department (PWD) has revealed that two slope failures occurred 20 to 30 minutes apart near the landslide area along B66 Seksyen 13.0 Jalan Batang Kali-Genting Highlands.
In a statement, PWD said this was the finding by its forensics team from the PWD Slope Engineering branch.
"The estimated dimensions of the slope failure are 70m (height), 120m (width) and 330m (length) with an estimated volume of rubble of 450,000 cubic metres.
"The failure mode is a combination of retrogressive and debris flow. The first slope failure most likely occurred in the camping area.
"The failure resulted in the area at the toe of the slope to become weak, which caused the occurrence of a subsequent (second) larger collapse.
"Active underground water flow was detected in the location of the collapsed slope, especially in the campsite area," it said.
PWD added that visual inspections at the road and slope at the section had found that the drain nearby was clean, dry and not clogged, which showed that there was no problem in the drainage system.
"The sidewalk along Jalan B66 Seksyen 13.0 from Goh Tong Jaya to Batang Kali has fallen and was damaged because of the landslide.
"There were also lengthwise tension cracks on the left lane heading towards Batang Kali due to the landslide. The roadside drain had also broken off."
The department added that based on its findings, soil saturation and high pore water pressure due to the accumulation of underground water at the bottom of the slope had weakened the toe of the B66 road slope.
This subsequently caused retrogressive failure to the road slope.
"In order to prevent further collapse, PWD has implemented short-term preventive repair work, which is to immediately cover the exposed slope surface with a tarpaulin sheet.
"We also diverted existing surface drainage water from the left drain to the right drain to prevent running water from entering the area, and installed tilt sensors to monitor ground movement at the site," it added.
The PWD said a detailed ground investigation was expected to be carried out at the site once search and rescue operations were completed.