PENANGITES need not worry about ground movement, vibrations or even landslides from the “drill and blast” method to be used in the construction of the Pan Island Link (PIL 1), according to a geotechnical expert.
In allaying concerns over the suitability and safety of the drill and blast method of rock excavation, Datuk Dr Gue See Sew explained that it was the most common method used for tunnelling in granite that has been adopted in Malaysia since the 1970s, including for the Genting Sempah Tunnel (Karak Expressway) and Menora Tunnel (North South Expressway).
“The drill and blast method is a safe and established method that takes into consideration all aspects related to ground movement and settlement.
“It is used even in Taiwan which is within the seismic fault zone. The relevant areas are prepped in advance with preventive measures such as pre-grouting in permeable faults and strengthening using steel ribs and rock bolts in areas with weak zones.
“These are standard techniques to tackle water seepage and ensure the stability of tunnels,” he said.
Gue added that drill and blast is also used in Hong Kong, which, like Penang, is predominantly granite formation and far more densely populated.
He also addressed concerns over the effects of tunnelling on important structures such as the Kek Lok Si Temple, Air Itam Dam and Penang Hill Funicular Railway, explaining that these structures are not even close to the drill and blast site.
It has been reported that Kek Lok Si Temple and the Air Itam Dam are 500m away from the alignment, while the tunnel for PIL 1 is more than 150m below the Penang Hill Funicular Railway.
“The drilling and controlled blasting has negligible impact in terms of vibration and settlement to structures or buildings beyond a distance of 100m from blast points,” Gue said.
“With proper design and blast control measures in place, vibration and settlement to neighbouring structures can be controlled even at a distance less than 10m, evident from the recently completed Klang Valley MRT Line 1 where tunnelling was done with live traffic on top!
“Some recorded vibration and noise levels measured as close as 8.7m were found to be within limits and the works were successfully carried out without major incidences.
“There is a zone of influence that will be pre-determined, but that can be complied with, can be done and has been done,” said Gue who is serving as commissioner for both Commissions of Inquiry set up in Penang to investigate three incidences over the past years – the Menara Umno building failure and Second Penang Bridge ramp collapse in 2013, and the landslide at the Tanjung Bungah construction site in October 2017.
Gue said that as part of Department of Environment requirements, settlement and vibration monitoring of adjacent structures will need to be carried out to ensure safety of adjacent structures.
He also clarified that there is no concern that the vibration from the blast would cause the soil in Penang Hill to loosen.
“Beyond the tunnel entrance, most of the controlled blasting will be deep below ground and enclosed, unlike in a quarry where blasting is carried out in the open. Cracks, if any, will be sealed promptly after blasting,” he assured.
The PIL 1 is an integral part of the Penang Transport Master Plan (PTMP), designed to solve the island state’s traffic congestion and cater to the economic needs of Penang over the next five decades.
The first phase of the PTMP is the construction of the PIL 1 and the Bayan Lepas LRT. Currently, the Tun Dr Lim Chong Eu (LCE) Expressway is Penang’s only spine road which is perpetually congested.
PIL 1 is expected to serve as a second link with a ring traffic dispersal system connecting North Coast Paired Road (NCPR), Gurney Expressway, LCE, Penang Airport, and, the first and second Penang bridges.
Meanwhile, the Bayan Lepas LRT is expected to meet the public transport demand along the congested LCE corridor and will form the main backbone for connectivity between the island and the mainland.