Bromford Tunnel extension – design and environmental benefits with no additional land take

Background and industry context

Bromford tunnel, located at the eastern edge of Birmingham, forms part of the Main Works Civils Contract (MWCC) for the northern section of the High Speed Two (HS2) Phase One scheme; its extension is proposed in line with the findings of the Oakervew review ^[1], completed in 2020, regarding how to take forward HS2 – notably in respect of achieving cost savings without undue delay to the project.

Increasing the length of Bromford tunnel removes the need for sizeable elements of above-ground infrastructure, including retained cuttings, retained fills and a viaduct, bringing benefits such as reduced impacts on a local nature reserve (Park Hall) and agricultural land, avoiding the need to locally realign the River Tame, and removing a number of noise, landscape, visual and heritage impacts by placing railway infrastructure below ground. However, the need for additional shaft infrastructure and a relocated portal, together with changes in the way the scheme will be constructed, all have potential environmental consequences. Furthermore, in order to complete construction of the extended Bromford tunnel, an Order under the Transport and Works Act 1992 is needed, which will provide for the design change from viaduct to tunnel through an amendment to the High Speed Rail (London – West Midlands) Act 2017 (the HS2 Act 2017). An additional consideration is the fact that deemed planning permission would not apply to the works if they were likely to have significant effects on the environment that are not already covered by the Environmental Statement in connection with the HS2 Act 2017.

To appraise the environmental implications of design change in the context of the above consenting requirements and meet HS2’s Environmental Minimum Requirements (EMRs)^[3], environmental assessment work was undertaken in tandem with developing the design change; the resulting scheme evolution is outlined in the remainder of this case study.

Approach

The consenting and compliance context set out above prompted an iterative design and environmental assessment process to be carried out, in turn enabling integrated environmentally orientated design and construction solutions to be found by the project team. This context also necessitated considerable consultation and engagement with relevant government departments, local authorities and wider stakeholders, which will continue to be required as the project moves forward. The key environmental challenges presented by design change, together with the solutions found, are outlined below.

The tunnel will be extended from under 3km to nearly 6km long; once a tunnel exceeds 3km in length an intermediate shaft is required to facilitate the safe flow of air within the tunnel. How will the additional shaft that is required be accommodated without undue environmental effects?

Without careful siting and design, new shaft infrastructure has the potential to introduce new and significant environmental effects. To avoid additional land take, the original site of the eastern portal (with 2 storey portal building), in the Castle Bromwich Business Park area, was utilised for the shaft and associated ancillary components, including a 2 storey headhouse and compound at ground level. The siting and design solution taken forward will result in a net reduction of land take in the Castle Bromwich Business Park area, compared with the HS2 scheme at the time of the HS2 Act 2017, and in other respects would result in a scheme which contributes similar above-ground built form to the local urban environment. This will mean that fewer properties and businesses will be affected, saving jobs in the area and reducing socio-economic effects, whilst avoiding new or different significant adverse effects in respect of other environmental considerations.

The eastern portal will be located further east as a result of the extended tunnel – are there environmental considerations associated with this location for permanent infrastructure and, if so, how have they been taken into account?

The new location for the eastern portal lies close to the village of Water Orton, within the Green Belt. Key environmental considerations include agricultural land, historic environment, landscape, visual amenity, biodiversity, noise and the water environment, together with the potential for combined effects on community and health.

To facilitate the avoidance of additional and significant environmental effects, the eastern portal will be situated at the location of the 13m deep HS2 Water Orton cutting. The cutting will be shortened by approximately 600m, from its western end, to accommodate the portal. This will avoid the need for the permanent scheme to additionally affect agricultural and ecological receptors. In addition, the portal has been carefully sited outside of the floodplain to minimise flood risk. Furthermore, a comprehensive landscape scheme has been developed to integrate the proposals, including portal and portal buildings, with the semi-rural surroundings, incorporate biodiversity measures (such as woodland planting for pipistrelle bats), and avoid new significant effects in respect of ecology, landscape, visual amenity and the historic environment.

To minimise the noise of trains as they exit the tunnel, a porous portal will be constructed. The purpose of a porous portal is to ensure that the sound waves produced by the ‘piston effect’ of the train moving at speed, which can otherwise result in noise as the train exits the tunnel, are kept at a level which does not adversely affect the surrounding area. A porous portal is generally achieved by providing perforated structures, usually of concrete, at the tunnel entrances.

The measures outlined above will avoid new significant, permanent effects on the environment, including in-combination effects relating to community and health.

A longer tunnel will result in changes during the temporary construction phase, such as the need for management of increased spoil. How will potential environmental impacts associated with these changes be managed?

An extended tunnel has the potential to increase heavy goods vehicle (HGV) movements associated with removal of additional excavated material (tunnel spoil) from the tunnelling location, with knock-on traffic, noise, air quality, community and health effects.

The scheme put forward at the time of the HS2 Act 2017 planned for tunnelling operations being driven from the west portal. Taking account of the potential environmental issues above, the tunnel extension scheme reverses the direction of the bore, so that it is driven from the east portal (at Water Orton). This change to construction planning and logistics means that purpose-built haul roads can be constructed within land already being used by HS2 and not on the local road network, in order to transport tunnel arisings from the eastern portal for use on HS2’s nearby Water Orton flyover, Marsh Lane embankment and other assets.

As a result of this, there will be up to 260,000 fewer HGV movements on public roads over the course of construction. By avoiding the local road network for mass haul operations, corresponding traffic and transport effects, together with associated air quality, noise, community and health effects, can also be avoided. Furthermore, the overall reduction in HGV movements on public roads helps to minimise such environmental impacts over a wider area during construction.

However, before tunnel arisings can be utilised, they must be treated and handled appropriately, which introduces the need for a slurry treatment plant, conveyors and other plant on site. Whilst construction compounds had been planned near Water Orton at the time of the HS2 Act 2017, to carry out works in this area, store materials and serve as a base for the workforce, the introduction of additional plant gives rise to the potential for new and significant temporary noise impacts. These impacts will be avoided through a combination of low-noise enclosures around those parts of the compound that can be enclosed and noise barriers to screen open parts of the compound site such as conveyors and material storage areas. Temporary re-housing of nearby residents and installation of noise insulation at surrounding residential properties will also be implemented, if required.

The change to tunnel boring strategy outlined above also necessitates relocation of the substation required for tunnel boring and subsequent operation of the HS2 railway. The responsibility for substation delivery sits with the relevant statutory undertaker, with whom the project team are engaging as they take this forward at a location off the Birmingham Road, near the edge of Birmingham.

What are the implications of the design change with respect to carbon emissions and climate change?

Through reducing the overall extent of built infrastructure, the design change will reduce route-wide carbon emissions by an estimated 20,000 tonnes, compared to the scheme at the time of the HS2 Act 2017. In terms of resilience to climate change, whilst there would be a risk to overheating within the tunnel as a result of potential future increases in air temperatures, this will be mitigated by the ventilation systems in the tunnel design, including provision of a shaft at the appropriate location. A reduction in flood risk due to relocation of the portal outside of the functional flood plain brings benefits in terms of resilience to future climate change.

Outcomes

Bromford tunnel extension will meet HS2’s environmental requirements, challenging in itself, as outlined above, and include the following principal net environmental improvements over and above the scheme at the time of the HS2 Act 2017:

• removing the need to locally realign the River Tame;
• reducing environmental impacts to Park Hall nature reserve;
• reducing the amount of agricultural land affected;
• removing multiple landscape, visual and historic environment impacts by placing railway infrastructure within extended tunnel rather than on the surface;
• reducing operational airborne noise for a number of properties by placing
• exposed track in tunnel, in the vicinity of those properties;
• relocating the eastern portal out of an area of floodplain and placing the railway in tunnel beneath it, in turn reducing climate change effects due to reduced
• flood risk;
• accommodating new shaft infrastructure whilst simultaneously reducing land-take and corresponding socio-economic impacts within Castle Bromwich Business Park;
• reducing HGV movements on public roads during construction, through construction planning and logistics, in turn reducing traffic and associated air quality, noise, health and community impacts; and
• reducing carbon emissions due to the reduced overall extent of built
• infrastructure.

Learnings and recommendations

Key learnings from the project are as follows:

• Clearly defining the scope of the project from the outset, drawing on previous options analyses and associated stakeholder engagement, was key to efficient and effective environmental assessment thereafter.
• Assessment involved comparative analyses, given the project constitutes a change to the already consented HS2 scheme, such that previously considered environmental topics were necessarily considered. However, early project definition enabled the specialists concerned with each topic to identify and focus on the key issues at hand, helping to drive appropriate, targeted design solutions and reflect these in environmental assessment reporting.
• Early collection of information about environmental conditions (“the baseline”) in the vicinity of the project, given the elapse of time since the HS2 scheme was consented, and that to inform prediction of future environmental conditions without the HS2 scheme (‘the future baseline’), was essential to allow this information to feed into the iterative design and assessment process, facilitating responsive design.
• Collaborative design development enabled truly iterative design and environmental assessment to generate integrated solutions. Information sharing, via SharePoint, and regular project design and progress meetings, involving leads from the project management, legal, consents, environmental, engineering, construction planning and communications teams, enabled these team to contribute effectively to the process, with the communications team instrumental in providing feedback from stakeholder engagement for consideration as the design progressed.
• Allowing sufficient time for the collaborative and iterative design process provided the opportunity for the effectiveness of solutions to be tested and then, where necessary, refined.

Bromford tunnel extension brought challenges that needed to be overcome in order for HS2 to meet compliance and consenting requirements. Integrated project management, design, environmental, legal, consents and communications teams, across HS2 and their supply chain, enabled holistic solutions to be found, taking account of environmental, social and economic considerations as well as responding to functional and financial drivers. One of the greatest challenges, which remains so, is taking third party partners, consultees and stakeholders along on the change journey for such a complex engineering scheme. The solution lies in effective communication and engagement, informed by robust technical analyses, to enable key scheme information to be conveyed but also to facilitate design that is responsive to those whom it may affect.

Conclusion

The major design change represented by Bromford tunnel extension was achieved with no additional land take, whilst meeting HS2’s environmental requirements and achieving a diverse set of improvements. This was only possible by collaborative working between multiple teams across HS2 and their supply chain.

References

1. HS2 (2020) Oakervee Review of HS2.
2. UK Government (2017) High Speed Rail (London – West Midlands) Act 2017.
3. HS2 (2013) Environmental minimum requirements for HS2 Phase One.

Supporting materials

1. HS2 (2021) Bromford Tunnel Extension Environmental Impact Assessment Screening Report – Executive Summary
2. HS2 (2021) Bromford Tunnel Extension Environmental Impact Assessment Screening Report
3. HS2 (2021) Bromford Tunnel Extension Environmental Impact Assessment Screening Report Appendices
4. HS2 (2021) Bromford Tunnel Extension Environmental Impact Assessment Screening Report – Map Book