Technical, legal, and organizational investigation of the feasibility of circular management of excavated materials in large-scale underground construction—demonstrated through the extension of Vienna's U5 metro line.

Starting point / motivation

Large-scale civil engineering projects, particularly the construction of underground infrastructure, generate considerable amounts of excavated materials in Austria. The majority of this material is currently landfilled or recycled for low-value purposes, which is associated with high land consumption, intensive transport costs, and additional CO₂ emissions. In 2023, around 50% of over 23 million tons of uncontaminated excavated material (BA, A1, A2, A2-G) was landfilled in Austria (see BAWP Status Report 2025, reference year 2023).

One of the key obstacles is the prevailing practice of waste classification, which allows only limited conclusions to be drawn regarding the geotechnical suitability, recultivation potential, and industrial recyclability of the materials. Furthermore, recycling options have so far been assessed separately under waste legislation and geotechnical criteria, rather than being systematically integrated. However, studies in the field of underground railway construction indicate that while process-related contamination affects classification under waste law, it has little impact on the actual recyclability of the excavated material.

Contents and objectives

The aim of the project is to systematize the elements of circular management of material flows in underground railway construction. The exploratory project lays the groundwork for the implementation of a subsequent real-world laboratory in metro construction.

Material concepts for the circular management of large-scale construction sites require a systematic analysis of raw material–related and logistical potentials. The focus is on the development of innovative investigation methods to enable the separation, processing, and high-quality reuse of materials.

In addition, transport and logistics processes will be optimized, digital tools for managing material cycles will be applied, and relevant legal and regulatory frameworks will be taken into account. At the same time, new business models will be tested in order to increase efficiency and sustainability in underground construction.

Specifically, the exploratory project aims to achieve the following objectives:

• Systematization of utilization and recycling analytics
• Development of innovative recycling technologies for tunnel construction
• Reduction of greenhouse gas (GHG) emissions from transport
• Assessment of process-related impacts (use of conditioning agents)
• Digital dashboard for circular construction management
• End-of-waste status for secondary raw materials derived from tunnel spoil
• Circular enhancement of different tunnel excavation methods

Methods

Existing material concepts and feasibility studies will be reviewed and further developed in order to establish a robust basis for the real-world laboratory. The targeted use of excavated materials is intended to conserve resources, optimize transport operations, and reduce CO₂ emissions.

The exploratory project prepares the implementation of circular management of excavated materials prior to construction execution and lays the foundation for a subsequent real-world laboratory. It builds on existing preliminary investigations of the material flows of the U5 line (section 2), which were jointly developed by ROMM ZT, the general planner, and WIENER LINIEN.

The methodology comprises the systematic development and evaluation of strategies for circular material management: materials are analyzed with regard to their geotechnical and industrial usability; innovative recycling technologies for tunnel construction—particularly mobile processing plants—are investigated; and transport and logistics processes are aligned with direct reuse and CO₂ reduction objectives.

In parallel, process-related influences such as tunnelling methods and the use of conditioning agents on waste-law classification are evaluated, digital tools for the control and documentation of material flows are tested, and legal as well as public procurement frameworks are examined.

Finally, perspectives for circular process innovation across different tunnel excavation methods are explored in order to enable efficient and sustainable implementation in the real-world laboratory.

Expected results

The findings are intended to make a significant contribution to strategic decision-making regarding a subsequent real-world laboratory and further RDI projects. The exploratory phase supports the assessment across the following dimensions:

• Systematic analysis of technological and organizational innovation approaches, particularly in the field of material recovery and utilization of excavated materials
• Reduction of primary raw material use by up to 50% for specific rock fractions (quantification depends on the material composition of the excavated material)
• Development of new business models in the fields of urban mining and secondary materials trading
• Increase in regional value creation through local processing
• Support for decarbonization in transport and raw material sourcing across supply and disposal chains

Project management

Arch. DI Thomas Matthias Romm - forschen planen bauen ZT

Project or cooperation partners

WIENER LINIEN GmbH

Arch. DI Thomas Romm
Löwengasse 47A/7
A-1030 Vienna
Tel.: +43 (650) 984 84 88
E-mail: thomas.romm@romm.at
Web: www.romm.at