Structural issues from tunnelling is a common concern. Typically, a survey is done of potentially affected properties, in a wide zone of influence. The appointed Contractor has an obligation to ensure that any damage determined to be caused by tunnelling is fixed. In addition, as the tunnel is constructed, there is typically a structural lining installed to the tunnel. One of the key purposes is to mitigate movement in the tunnel structure, in the excavation that has taken place. The amount of settlement allowed, typically a very small amount, is defined in the Environmental Impact Statement and therefore the planning requirements to which the contractor needs to deliver the project.

If there is concern from a resident that there has been impact to their building, we can utilise very accurate satellite data which allows us to trace the surface movement during and after the tunnel excavation, to determine whether movement has occurred associated with the tunnelling activity. This is undertaken by an Independent Property Impact Assessment Panel.

So, there are a number of layers of protection in place for the public and a number of obligations on ourselves, and on the Contractor delivering the work.

Where damage has occurred it is typically within a short distance from the tunnel alignment (less than 50m). The Contractor is obliged under the planning conditions of approval to rectify any damage caused by tunnelling within six months of completion of construction.

The Contractor will be required under the DPIE conditions of approval to develop a geological model. This geological model will include all aspects of the tunnel, including its final configuration and all construction stages. The Planning Conditions of approval also set out the maximum allowed settlement that is required at surface level. For example, for buildings of two stories or less a settlement of 30mm has been allowed on previous projects. This is an extent of settlement that is not expected to do any damage.

The geological model will determine those buildings that are most at risk of exceeding the settlement allowance, and the Contractor is obliged to undertake a condition survey of those buildings prior to construction. On recent projects, the Contractor has been obliged to undertake condition surveys of any other residence where a resident wishes to avail of a survey. If there is damage to a building, a resident can make a claim. The Contractor may then acknowledge that the damage (cracking) has resulted from the tunnelling. If the Contractor wishes to contest whether damage is a result of tunnelling then the issue can be referred to the Independent Property Impact Assessment Panel. The IPIAP will then make a determination. As the costs of running the IPIAP are attributable to the Contractor, they have on recent projects referred fewer claims to the IPIAP.

Regarding how many number of claims, I understand that there are a number, much less than 50, currently in play on M4M5 Motorway which is a 7km long tunnel which will cross under thousands of properties. Of these cases most are in the St Peter’s Interchange area where there are inconsistent ground conditions, and significant merge and diverge alignment caverns. A tunnel under Blackheath is likely to have more consistent geological conditions and will not have the merge / diverge issues.

The upper strata of the Blue Mountains - the peaks and ridgelines - are predominantly made up of a number of sandstone and claystone layers with come localised basalt caps on higher peaks.

These layers are visible on the cliff faces, and this is the expected geology through which a Blackheath tunnel would be constructed. While most sandstone and claystone layers are expected to be good tunnelling media, the Banks Wall sandstone is known to have some unusual characteristics which will require some focus.

Further geotechnical surveys and investigations are required to determine the best path for a tunnel underneath Blackheath. Investigations to date have given no indication that a tunnel is not feasible underneath Blackheath.

The shorter tunnel option may require ventilation outlets. However, proposed portals for a longer tunnel are located away from where people live and work, which may mean ventilation outlets are not required. Further studies are required to determine the ventilation needed for either of the tunnel options.

As referred to in the presentation, we are undertaking studies with regard to possibly having emissions from the portals. This will only be possible if we can demonstrate to NSW Health and others that there is negligible impact in those areas to the residents.

We try and locate ventilation outlets as close as possible to tunnel portals. We can certainly consider this. Further studies are required to determine the ventilation needed for either of the tunnel options.

This is one of the discussions we had with the Co-Design Committee. Some of the road projects in Sydney have been delivered with a Road-Header Machine to excavate. In those tunnels in Sydney, we allow some groundwater into the tunnels, as it has been agreed with various governing agencies, particularly the Department of Planning and the EPA, that the groundwater in those areas is not sufficiently sensitive that we need to totally waterproof the tunnel.

What might we do differently here to protect the sensitive environment here in the Blue Mountains? Sydney Metro is being constructed using a Tunnel Boring Machine (TBM). It excavates and then installs pre-cast segmental concrete lining, with seals between the concrete lining which effectively achieve a waterproof solution, so for Blackheath, using a TBM would be a larger scale, but could provide a waterproof sealed construction.

In the presentation, we referred to the term ‘no adverse impact on groundwater’. The NSW Aquifer Interference Policy defines methodologies by which we can demonstrate ‘no adverse impact’. Part of the evidence is defined by using analysis methodologies, investigation methodologies, monitoring methodologies, which are defined in other documentation such as the Australian Groundwater Modelling Guidelines. These are proven methods designed by others that Transport for NSW and our consultants would need to adhere to, in order to deliver the defined tunnel solution.

We have already received feedback regarding the importance of surface features such as hanging swamps, as well as underground water features such as aquifers in the area.

We are committed to minimising impacts on the environment, including groundwater sources, and will develop an option with minimal interference. A full assessment of impacts will form part of the Environmental Impact Statement.

Typically, we don’t stipulate the construction method. The Road Header technique has typically been employed in Sydney. One of the issues that may lead us to a TBM solution here, is that there are no merge or turns or changes in the cross section, which could lend itself towards a TBM solution. There are various types of TBM, and the best suited to the geology here might be a double-shield TBM, which allows us to excavate and install lining in a very efficient manner.

We haven’t assessed how that equipment would be delivered, but I would refer people to the Super Tunnel series on SBS recently. It’s certainly a logistical challenge.

Obviously not if the projects were being excavated concurrently. Every possibility that it could be used. The geology would be similar but not the same. And the advantage would be that the cross section would be the same. Might need to specify certain aspects of the TBM as to how it goes through the most adverse ground conditions.

We’ll be listening to the feedback from the community, considering a range of issues, environmental, community, constructability, and other factors, and making a decision based on the best outcome from all of those issues.

As a tunnel has been selected as the best option for the highway upgrade through Blackheath and endorsed by the community, duplication of the existing highway through Blackheath is no longer being actively progressed by Transport for NSW.

The NSW State Government is committed to investigating the tunnel option at this time. We are currently not developing the surface road solution any further, but we are interested in any improvements you may want to suggest to improving the safety, amenity and connectivity of the existing Highway.

Yes and we will likely duplicate the safety station on either side of the highway, which will increase safety.

This is highly unlikely; the location of the station is highly dependent on the final location of the northern portal. This is a very early stage of design, but we anticipate that the Heavy Vehicle Safety Station will most likely need to be moved. Transport for NSW would look to enhance safety by having a checking station on each side of the Highway, in a location which will service all heavy vehicles using the tunnel.

All minutes from the BCC process were posted on our project website shortly after each meeting. The minutes and the report which covers the BCC process and outcomes are available here: https://www.rms.nsw.gov.au/projects/great-western-highway/katoomba-to-lithgow/index.html under the section ‘Blackheath Co-Design Committee’.

A Transport for NSW Policy is currently being developed to inform whether any dangerous goods would be allowed through a Blackheath bypass tunnel.

At this stage heavy vehicles will not be mandated to travel through a Blackheath bypass tunnel, and it is yet to be determined whether vehicles carrying dangerous goods will be allowed through a tunnel.

However unless those drivers have deliveries or are picking up goods within the Blackheath township it will be faster for them to choose to travel through the tunnel.

As in the draft designs, a service road would be constructed parallel to the highway that links those up and they would then access the highway at Valley View Road.

Yes, two lanes each way.

Two lanes each way.

This is something we could consider, however around half the freight in the Blue Mountains is carried by road, including refrigerated goods, fuel, livestock, commercial and retail goods. Nearly 40 per cent of this road freight either begins or ends its journey within the Blue Mountains, supporting the local economy. We need to ensure that any tunnel addresses the service needs for this freight.

The posted speed limit will be 80km/hr.

Please visit the virtual consultation room at https://www.rms.nsw.gov.au/projects/great-western-highway/katoomba-to-lithgow/interactive-portal.html

Spoil could be used to fill in a quarry, and provide new amenity, as in Hornsby where a quarry was filled and a new public park was formed.

There are potential reuses across the duplication project but these have not been established yet.

Unfortunately, we are not advanced enough in the project to provide a figure for this.

As we go through more detailed design, we’ll be looking at the absolute best location. As you go towards Mount Victoria, there is the constraint of World Heritage Area, and Browntown Oval.

The proposed entry at Sutton Park would have an impact on 12 residential properties at the end of Evans Lookout Road, Brightlands Avenue and Chelmsford Avenue. Transport for NSW is speaking directly with any potentially affected property owners.

Nearby properties could be impacted by noise, dust, vibration, but we would have environmental management plans in place to deal with those issues.

Yes, we would have to acquire land from National Parks. This requires a special parliamentary process, which we are planning to undertake.

No, we are not considering a toll.

Around 3%. We would try to ensure that this is not too steep, to limit noise, pollution and any traffic impacts.

In the current draft designs, the route does go under the railway. Our designers need to pay close attention to the crossings, to make sure they can support all of the loads that go over the top. There are a number of considerations to make sure there are no impacts to the railway tracks.

There is precedent in our consideration of issues for us at similar depths with NorthConnex, where the rail crosses over the tunnels.

You can visit the online consultation room at https://www.rms.nsw.gov.au/projects/great-western-highway/katoomba-to-lithgow/interactive-portal.html

We're taking our advice from NSW Health and avoiding face to face consultation for the time being. We absolutely need to avoid creating any health risks for the community. For anyone who is unable to use our online resources, we are happy to speak over the phone, please call 1800 953 777.

Construction could take up to four years.

Typically any construction outside a tunnel would be standard construction hours, so five days a week, Monday to Friday 7:30- 5:30, and possibly a half day on a weekend, dependant on the Environmental Assessment. Underground, tunnelling can be 24/7, particularly with use of acoustic shielding.

We are unable to confirm a start date as yet, as there are a number of studies and investigations still to be undertaken. If you wish to be kept up to date with the project, please email the project team at gwhd@transport.nsw.gov.au

In the first half of 2021; please email the team at gwhd@transport.nsw.gov.au to sign up for project updates.

We expect to be able to come back to the community in the first half of next year to announce the preferred portal option. Along with broad community consultation, we need to properly consider all of the issues and impacts to determine a final location for the portals at each end of the tunnel.

This particular project is looking at a road solution. Other parts of Transport are considering rail solutions.

The NSW Government is committed to moving more freight from road to rail and is investing in the rail freight network to increase capacity. The NSW Government has also committed to investigate improvements to the rail corridor for commuters through the Faster Rail strategy. 

The rail line provides a reliable service for Blue Mountains commuters; however, the highway will remain a vital link for the Central West and the Blue Mountains and there is no substitute for upgrading the highway as we need both road and rail to meet current and future demand.

Around half the freight in the Blue Mountains is carried by road, including refrigerated goods, fuel, livestock, commercial and retail goods. Much of the freight currently on the road network requires direct access to freight hubs, such as retail precincts, light industrial areas or home deliveries. 

The 10 storey analogy is just to demonstrate approx how far underground the tunnel will be.