Friday, September 20, 2013

Told you it was underground erosion didn't we?

This was what we wrote on JUNE 18, 2013. 
Far from being solely an “impact crater” as implied by Clifford Tan and The Star; the 6m deep crater which Lim's car had “sunk” into was a cave-in (collapsed) crater, a consequence of both deep impact and existing underground weaknesses like erosion voids beneath the road foundation. The volume of upheaval mass did not equal the volume of the observed crater.

There are significant differences. An impact crater on solid ground would have the typical bulge (upheaval) at the peripheral of the crater (as in a meteor crater) and have the impact debris thrown all around it. Remember the Conservation of Mass law?
In fact all the evidence point to an additional cave-in collapse of an existing undetected below the road foundation void (underground cavity). Underground cavities ranging from a few inches to a few metres, can remain undetected on the surface due to the “arching effect” of the overlying supporting 'roof layer”.

Knowing Penang so well, there are probably a lot more cavities caused by underground erosion. That explains the “missing masses” in sudden cave-ins or collapsed sink holes. Macalister road is one of the oldest road in Penang and was already “warping” here and there when I was a boy cycling to school. The layers of bitumen and road foundation added through the years helped to strengthen the “roof support” and kept the road from caving-in until the forceful impact of the falling concrete beams and lightning arrestor.

Another sinkhole appears at lightning arrester collapse site

GEORGE TOWN (Sept 11): Another sinkhole has appeared in front of Menara UMNO at Macalister Road today, the site where 44-year-old economy rice seller Lim Chin Aik is believed to be buried after the building's lightning arrester collapse on June 13.     
The sinkhole, estimated at 0.5m in diameter and two-metre deep was spotted by a passer-by about 1.15pm today. 
Komtar Assemblyman Teh Lai Heng, said he received a phone call on the matter and rushed to the scene with a Penang Island Municipal Council (MPPP) officer.  
"The sinkhole could be caused by continuous rain over the past few days which has washed away the soil underneath," he told reporters at the scene.  
The MPPP officer however said apart from the rains it could also be due to minor leakages in an underground pipe.  
"We cannot determine the actual cause so we have informed Indah Water Konsortium (IWK) to check it out," said the officer, adding he was not sure how long it would take to cover the sinkhole.

Read more:

Thursday September 12, 2013 MYT 7:19:34 AM
Sinkhole opens up near site of lightning arrester collapse

GEORGE TOWN: Traffic along Macalister Road here slowed down to a snail’s pace after a sinkhole appeared on the road, near the site of the lightning arrester collapse which killed a motorist in June.
The hole, measuring about 0.6m in diameter and 1m deep, is located in the middle of the road in front of the Pakistani Mosque.
Komtar assemblyman Teh Lai Heng said a preliminary probe by the Penang Municipal Council’s engineering department showed that a leaking sewerage pipe about 3m away had caused soil erosion beneath the road, resulting in the cave-in at about 1.15pm yesterday.
He said the section of the road had been cordoned off and an iron plate would be placed over the sinkhole for the time being.
On Aug 14, a forklift fell into a hole when the road in front of the Pakistani Mosque caved in during work to repair damage caused by the lightning arrester collapse.

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