So what if there are faults in granite? You can still build tunnel

By CN Ng

Dr Kam Suan Pheng in her presentation organised by the Penang Forum raised numerous objections against the 19.5km Pan Island Link 1 (PIL 1) highway project.

Many of them pertain to geological factors which lay people may not be sufficiently familiar with to discern the truth from the spurious.

As her views are now reaching a wider audience via news portals, a presentation of alternative arguments is necessary so that public opinion can be formed on a more informed basis.

Below is a list of the issues or concerns raised by Kam, based on her geological considerations as reported and which can be obtained from the online video of her talk. Against each of them is my perspective as a geologist:

*Issue #1: Granitic rock has naturally occurring faults where water would usually seep through which could be disastrous during tunnelling.

It is true that faults do occur naturally in granite and water can seep along them but it is alarmist to conclude that tunnelling through them “could be disastrous”. It is akin to saying that crossing a busy road could be disastrous (and therefore should be avoided).

Among all the tunnels built all over the world, it would be hard to find one through granite or any rock that are free from faults or other discontinuities.

Precisely because faults are so common and the dangers they can pose are so serious that faults and other discontinuities are almost always among the first geological features to be identified during the investigation for any tunnel.

To abort a tunnel just because its alignment crosses one or more faults would make as much sense as we avoiding crossing all roads for fear of being run down by cars.

In planning a tunnel, you just have to check them out and be prepared for them just like you have to watch out for oncoming vehicles before crossing a road.

*Issue #2: The Air Itam Dam is a 56-year-old earth dam and is extremely fragile. Perched 235m above sea level, the slightest movement would bring gallons of water gushing down the Ayer Itam valley. This is based on red flags from the EIA report, indicating that “collapse and subsidence” may occur as a result of tunnelling through the fragile areas near the fault lines. Areas intersecting with the fault lines are highly fractured and vulnerable to collapse.

First of all, what is the basis for saying that the dam is “extremely fragile”? Was its design flawed, its construction faulty, or has the structure itself deteriorated over time?

Here, the blame is not entirely on Kam because the EIA report itself has planted the seeds of suspicion and fear with words like “risk of sudden collapses, subsidence and sinking that can damage both the work under construction and existing nearby structures” (condominiums, Kek Lok Si Temple, Air Itam dam and Bukit Bendera complex).

However, the crux of the matter is not whether such risks are real but under what circumstances they can arise and what the probability is of them occurring.

Any construction work can cause similar problems to an adjacent structure even if there is no fault nearby, but does that mean that there must be no construction next to any existing structure?

Or perhaps Kam is suggesting that tunnel construction is intrinsically much more hazardous, especially with the drill-and-blast method.

This tunnelling method has been used all over the world, including in Malaysia. It has even been used across cities beneath sensitive structures such as old buildings and even laboratories with delicate instruments.

For instance, the Stockholm Northern Link, an underground expressway consisting of two parallel three-lane tunnels was excavated this way. At one point only seven metres of rock roof separated it from the Alba University Center above, where extremely sensitive equipment with resistance to vibration measured in µm/s were housed.

This is just one example of how drill-and-blast can be effectively and safely be used, even in close proximity to sensitive structures.

Therefore, fears about possible damage to the Air Itam Dam, nearby condominiums, the Kek Lok Si Temple, and the Bukit Bendera complex are completely unjustified if standard due care is exercised.

The claim that the Air Hitam Dam is “extremely fragile” to the point of being susceptible to damage by the construction of the tunnel or the viaduct down the valley, 500m or 600m away (depending on which part of the EIA report you want to pick the figure from) is particularly irresponsible, especially when embellished by the scenario of water gushing down the valley (to Air Itam town below).

*Issue #3: No mention of the stability of the granitic bedrock and the impact on underground water flow.

In an EIA, a proposed project is evaluated for potential issues and these are not potential “issues” because granite is among the strongest and most impermeable of rocks. Therefore, not mentioning them is not wrong at all.

However, if there is any genuine concern over these issues, they can be raised in the form of written questions to the Department of Environment.

*Issue #4: 750,000 lorry loads of debris: 2.5 million cubic metres of rock debris using 5-tonne lorries over 3 to 4 years.

The issue being raised by Kam here is apparently on the large number of lorry trips that will probably worsen the traffic woes of Penang during the project period.

It has nothing to do with geology but a brief discussion here is useful because it illustrates how the wrong choice of parameters can turn a normal condition into an issue.

Kam has not revealed how she arrived at the 2.5 million cubic metres of rock debris and from there transformed into 750,000 lorry loads of five tonnes each.

Assuming that her estimate of rock debris is right, that would yield 6,875,000 tonnes of debris since the density of granite is about 2.75. This would require 1,375,000 trips to move is if indeed five-tonne lorries were used.

However, commercial lorries used for transporting quarry products and similar materials are normally of at least 18-tonne capacity and this would work out to about 382,000 trips, far less than her unrealistic assumption of using five-tonne lorries.

It is possible that even bigger lorries would be used to keep costs down and hence further reduce the number of trips and therefore the problem.

*Issue #5: 700kg of explosives will be needed to blast through the hills.

Again, this is not an issue directly related to geology but nonetheless it is necessary to point out another flaw in Kam’s arguments.

If the EIA report, specifically Table 5.4.1, had been carefully read, it would be clear that the quantity of 700kg of explosives referred to is for each cycle of drill-and-blast which will yield about 4m of progress along the tunnel. It is not for the entire tunnel.

Concluding remarks

It is important that we are vigilant about our environment and to question the justification and safety of proposed works, especially when they extend over large areas and therefore have high environmental impact.

However, the questions we raise should be based on real concerns and sound reasoning. Use of false assumptions and dubious arguments will undermine our own credibility and help defeat our own objectives.

CN Ng is an FMT reader.