Underground infrastructure projects pose significant environmental risks due to resource consumption, ground stability issues, and potential ecological damage. This review explores sustainable practices for mitigating these impacts throughout the lifecycle of underground construction projects, focusing on recycling and reusing excavated tunnel materials. This review systematically analyzed a wide array of sustainable practices, including on-site reuse of excavated tunnel material as backfill, grouting, soil conditioning, and concrete production. Off-site reuses explored are road bases, refilling works, value-added materials, like aggregates and construction products, vegetation reclamation, and landscaping. Opportunities to recover and repurpose tunnel components like temporary support structures, known as “false linings”, are also reviewed. Furthermore, the potential for utilizing industrial and construction wastes in underground works are explored, such as for thermal insulation, fire protection, grouting, and tunnel lining. Incorporating green materials and energy-efficient methods in areas like grouting, lighting, and lining are also discussed. Through comprehensive analysis of numerous case studies, this review demonstrates that with optimized planning, treatment techniques, and end-use selection informed by material characterization, sustainable practices can significantly reduce the environmental footprint of underground infrastructure. However, certain approaches require further refinement and standardization, particularly in areas like the consistent assessment of recycled material properties and the development of standardized guidelines for their use in various applications. These practices contribute to broader sustainability goals by reducing resource consumption, minimizing waste generation, and promoting the use of recycled and green materials. Achieving coordinated multi-stakeholder adoption, including collaboration between contractors, suppliers, regulatory bodies, and research institutions, is crucial for maximizing the impact of these practices and accelerating the transition towards a more sustainable underground construction industry.

How to fill the empty annular space behind the segmental lining of tunnels is considered one of the most important questions in mechanized excavation, of which the main aim is to minimize settlement on the earth surface. In addition, the grout is the agent that creates a suitable bed for the segment lining of the tunnel and helps with its tightening. There are different methods of filling the empty space. One of them, using excavation by Earth Pressure Balance-Tunnel Boring Machine (EPB-TBM), is the injection of two-component grout at suitable pressure to the back of the segment as the shield of the excavator moves ahead. The grout utilized has suitable mechanical characteristics and efficiency. The main properties of grout refer to bleeding, fluidity and the results of the Marsh funnel test (ability to pump grout), setting time, gelling time (to avoid grout washing out) and compressive strength of grout (to minimize settlement on the earth level). The present study attempts to review the effect of any constituent materials of two-component grout on the parameters. Consequently, different tests with various constituent materials on the properties of grout were conducted.

An accurate determination of Hoek–Brown constant m_i is of great significance in the estimation of the failure criteria of brittle rock materials. So far, different approaches such as rigidity index method (R-index), uniaxial compressive strength-based method, and tensile strength-based method, and the combination of these two methods (combination based method) have been proposed to calculate the value of m_i. This paper aims to thoroughly review the previously existing methods to calculate the value of m_i and make comparison between the obtain results to propose the new material constants that provide the best fit with the experimental data. In order to fulfill this goal, a large number of data for different quasi-isotropic intact rock types from the literature were collected and statistically analyzed. Additionally, based on rock types, new material constants are introduced for igneous, sedimentary, and metamorphic rocks. The obtained results proves that for different rock groups (igneous, sedimentary, and metamorphic rocks), R-index method provides the best fit with the experimental data among the others, and it is also independent of rock type. Interestingly enough, there is significant differences in the predicted m_i values using different methods, which is more probably due to the quantity and quality of data used in the statistical analysis.