Concerns about tunnelling for Penang’s ‘monster highway’

Make sure you head down to Spice for the ‘town hall’ meeting with the Department of Environment on Thursday, 22 20 September at 8pm regarding the EIA for the RM8bn 19.5km six-lane Pan Island Link, which includes 10.1km of tunnels.

Soil scientist Dr Kam Suan Pheng writes in response to a letter that appeared in the press:

I refer to the article posted in FMT by reader CN Ng on 01 September 2018 titled “So what if there are faults in granite? You can still build tunnel”.

As I pointed out at the beginning, the main purpose of my talk was to share with the public the findings of the environmental impact assessment (EIA) report for the Pan Island Link 1 (PIL1) highway project. The EIA report is a professional piece of work that is to be evaluated on its own merits and it is pertinent to flag issues that are revealed but not sufficiently addressed by the EIA study.

All the points concerning the geological and geotechnical aspects raised were extracted from the EIA report, and to quote more extensively from it:

On page 7-34 the EIA Report identifies the geology and geotechnical concerns to include:

Mass earth movements given the occurrence of highly fractured/jointed granite bedrock and fault zones; the lateral alignment of PIL1 cuts across at least two major fault lines; and

Ground movements and vibrations occurring during and after construction may affect natural ground and nearby existing structures.

In the executive summary, it is stated:

The construction of tunnels may cause a deformation of the soils that may trigger a collapse and subsidence. Areas that intersect with fault zones are highly fractured and vulnerable to collapse. This can damage both, the work under construction and existing nearby structures such as condominiums, the Kek Lock Si Temple, the Air Itam Dam and the Bukit Bendera complex.” (page ES-18), with the conclusion that the magnitude and duration of impact from construction of main tunnels (drill-blast method) is rated as “Medium to High” (Table 7.1 page ES-33).

Page 7-36 of the EIA report tabulates the potentially significant impacts associated with tunnel construction conditions and activities:

Condition/Activity:

The tunnel portals are at areas known to have granitic residual soil and/or colluvium with a high percentage of boulders. Occurrence of highly fractured/jointed granite bedrock is common especially at Paya Terubong-Relau and Sg. Ara. These are also areas with identified fault zones.

The construction of the tunnel cause a deformation of the soils and rocks around the excavation area/portal area.

Potential impacts:

Risk of sudden collapses, subsidence and sinking that can damage both, the work under construction and existing nearby structures (condominiums, Kek Lock Si Temple, Air Itam dam and Bukit Bendera complex).

High risk of sudden collapse can happen in areas that intersect with the fault zones in Paya Terubong.

Condition/Activity:

Interaction with surface water and/or groundwater.

Seepage could develop in the open cut areas, especially in the fractured zone area.
Excavation of tunnels has a draining effect leading to a generalized drawdown of groundwater.

Potential impacts:

Water resources impoverishment, pollution risk, and affect workers safety.
Seepage might lead to rock stability failure. Shall not be allowed.

If not completely waterproofed may result in qualitative changes of the groundwater, changes in surface stability.

Statements as quoted above from the EIA report reflect the seriousness with which the geological and geotechnical concerns are professionally expressed by the two geology and geotechnical consultants in the EIA study team.

The main point I made is that the EIA team should then have done due diligence to carry out more detailed investigations to determine the risk or safety factors associated with tunneling, specific to the existing conditions of the proposed project sites. Or in Ng’s words: “under what circumstances they (ie the risks) can arise and what the probability is of them occurring”.

Surely not conducting more detailed investigations, or not reporting if such investigations have been conducted, constitutes a serious shortcoming of the EIA report.

If the expert opinion by other geologists is that these concerns are unfounded and, quoting Ng, that “the EIA report itself has planted the seeds of suspicion and fear” then it brings to question if the EIA report is not only deficient but also misleading and whether it should be accepted on these grounds.

The other issues raised by Ng, questioning the amount of rock debris and quantity of explosives (which by the way was not mentioned by me in my talk, as can be verified from the online video of my talk) are the very questions that ought to be raised as omissions and vagueness in the EIA report.

It is incumbent on the EIA study team to estimate the amount of rock debris that would result from excavating 10.1km of twin horse-shoe shaped tunnels.

Our estimate is based on the cross section geometry of the tunnels as revealed in Figure 5.3.23 of the EIA report, reproduced here. It is not stated how many emergency cross passages will be constructed. The amount of rock debris to be transported away from the project site is obviously not trivial.

While it may be usual for large-capacity lorries to be used for transporting quarry products, it has to be taken into consideration that the access roads identified for the transportation have limited capacity for large trucks. For example, the single access road (shown in the photo at the top) for transporting rock debris and construction wastes from the south portal of Tunnel 1, the north portal of Tunnel 2 and the viaduct connecting the two portals, identified in Figures 8.4 (b) and (c) in the EIA Report, is narrow, winding and with limited space for road widening.

Ng suggested that “if there is any genuine concern over these issues, they can be raised in the form of written questions to the Department of Environment”. This is precisely what the talk was intended for, that the audience is told what is said and not said in the EIA report so that the public can raise their concerns in their feedback to the Department of Environment as allowed for in the Environmental Quality Act 1974 of Malaysia.