With concern that good, solid, conciliated guidance was missing on how best to manage tunnel spoil in environmentally and socially responsible ways, a study was launched by the International Tunnelling and Underground Space Association (ITA/ AITES) and last year a report was issued.

The guidance report – ‘Tunnel Spoil Handling, Treatment and Disposal Options from a Global Perspective’ – was the work of ITA’s Working Group 14 (focused on mechanised tunnelling), and in particular the Task Group 4. It weighs in at 96 pages, is highly- and well-illustrated, and is structured in 12 chapters over its first 77 pages – and in addition has Conclusions & Recommendations, References & Resources, and is backstopped with Appendices.

Generous use of tables, graphics, and with information from tunnel projects – Italy’s Santa Lucia and Sparvo projects; and, in the US, the Arrowhead, Second Ave Subway and Oars Tunnel projects – helps to inform with detail as the report develops its discussion and guidance on planning for and managing tunnel spoil.

While the report was developed through WG14, which is focused on mechanised tunnelling, in their Conclusions & Recommendations the authors note that their guidance is for “all forms of tunnel and underground excavation spoil materials”.

Their first note is that spoil is not only rock and soil – it often includes water, gases (e.g., methane, hydrogen sulphide, etc), odours, dust, contaminants (petroleum products, dry cleaning fluids, etc), and may have chemically acidic or base characteristics. There can be other materials, too, such as bentonite or asbestos.

Of course, where the spoil is generated is then under the control of authorities in a local area, and ways of measuring, documenting and regulating for management and then disposal options. This challenge rises for both sides – industry and regulatory – along with the increasing volumes of spoil generated, and the growing pressures as well as needs for minimal environmental impact. The report mentions “sustainably sensitive approaches.”

Given the widely varying approaches internationally, as volumes of tunnel spoil rises, the authors recommend that ITA along with national tunnelling organisations create a ‘road map’, or global guidelines, for the tunnelling industry.

The Conclusions & Recommendations of the guidance report – the ITA’s 26th – then goes on to focus on: Sampling & Testing; Reporting Requirements; Legal; Case Studies & Project Examples; Excavation Products; Residual Chemicals; and, Reprocessing & Repurposing.

 Under Sampling & Testing, the report’s authors note that construction approvals require successful preconstruction testing of materials and chemicals – and “it cannot be overstated” the importance to project safety that spoil testing programmes are built into initial concepts for projects and their designs.

This advocacy for early planning – which has to include some site sampling, of course – comes up again under the report authors’ theme of Products of Excavation. They say it needs to be part of the thinking being developed in the project concept and early design stages. Sampling, testing and “recommendations for proposed mitigation measures need addressed “long before any excavation has begun.”

Again, this is for all tunnelling – mechanised or conventional.

When thinking first about whether to go below the surface, it is at that point that planning needs to seriously look at what would come up to it – whether the spoil comprises be natural, existing pollutants, or added materials from possible options in potential construction processes. And, to look at all this within the local allowable rules.

Then, get all that understood during procurement, and then nailed into contract documents.

No deviation.

On the rules, when the report looks at the theme of Legal as well as considering regulatory matters, its authors note that changes in either of those, or both, can affect the option of choice in tunnel spoil disposal. They observe that such changes can even be to thresholds, such as on material properties, like pH values or grain size composition.

The authors add, therefore: “Interpretation and enforcement of current and future legal restrictions and requirements will also have impacts on the handling, treatment and acceptable spoil disposal options.”

Coming under the theme of Residual Chemicals, the authors note that there may restrictions on the use of industrial, even biodegradable, chemicals frequently used in soil conditioning and ground improvement actions. A cautionary note comes, then, on potential for hold-ups or more – “delays and deferments” to significant and strategically important infrastructure.

Not preparing sufficiently, therefore, is a risk that would hurt the rationale for the economic investment that is trying to be made.

They say – under the Products of Excavation theme, but it is a fit under Legal and regulations too – that: “Success of some challenging projects could well depend on the conclusions, recommendations and advance commitments, permits and approvals.”

So, early planning is vital.



Learning from challenges experienced by others is a further point of note raised by the report’s authors. They say to considering information from tunnel jobs that have met complicated, site-specific subsurface conditions, including ground and groundwater difficulties, and also instances of gases.

Under the Case Studies & Project Examples section, therefore, the authors see value in gathering details about the solutions found on those occasions. To help move the thinking in industry to a wider effort to do so, they call, again, for some initiatives led by ITA and national tunnelling organisations to consolidate such lessons on how projects solved tough challenges of spoil handling, treatment and disposal. The authors would like to see both guidance and a database come about through that effort.

Such lessons could also show ‘green’ solutions as well, and also where existing industries as well as new techniques provided solutions to tunnel spoil problems.

“These goals would also score well for social and economic benefits,” they add.

The final theme in the Conclusions & Recommendations is Reprocessing & Repurposing – i.e., crushing & screening, and use for backfills & land reclamation.

The authors see “opportunities for vast quantities of tunnel and spoil material” and say tools to help get more of such would include use of: matrix analyses; decision trees; quantity estimates; work-inmotion studies; and, advanced chemical and material processing analyses.

They end by pointing back to the start – emphasising that upfront, early thinking will not only pay-off in derisking on spoil management but “potentially lead to many additional, attractive and economical solutions.” It’s a fit with circular economy thinking, and more economic strategy.

In their Acknowledgements, the authors point to the prior joint work by WG14 and WG 15 (Underground and the Environment) that contributed to a preceding report, in 2019 – ITA’s Report No 21: ‘Handling, Treatment and Disposal of Tunnel Spoil Materials.’ The new report build upon that initial work and draws upon industry conversations, consultations, contributions and questionnaires.

The results of a literature study called ‘Use of Excavated Materials from Tunnels and Deep Excavations’, by students at Warsaw University of Technology, in Poland, are also acknowledged.