To solve the engineering problem of the first tunnel lining cracking caused by the second tunnel construction of double-arch highway tunnels, a research method combining distributed optical-fibre monitoring, inversion analysis and numerical simulation that can reflect lining cracking was presented. Optical fibres were laid on opposite sides of the steel arches inside the first tunnel lining. Embedded optical-fibre monitoring was conducted continuously during the second tunnel driving. Based on the fibre-optic strain profile, the lining cracking was deduced and warned in time. The mechanical behaviour of the steel arch was investigated by the inversion analysis, which took into consideration the integrated impact of axial force and flexural moment. A two-dimensional (2D) load-structure method-based numerical model was established, considering the influence of different load distributions in each construction condition. The total strain rotating crack constitutive model was applied to reflect the cracking behaviour of concrete lining in the simulation, and the model was calibrated and verified in the laboratory. Comparative analysis between the simulated strain distribution and the distributed optical-fibre monitoring results was carried out. The deformation mode and crack distribution of the lining were analysed. The cracking mechanism was explained. Specifically, the second tunnel construction led to the loading at the top of the middle partition wall and the release of rock pressure in the first tunnel. Under these load changes, the secondary lining of the first tunnel cracked on the inner side of the top of the middle partition wall owing to tension, and compression-bending failure occurred near the right arch foot. Finally, the influence of the parameters on the lining force was analysed, and a construction optimisation scheme was proposed.

Urban underground infrastructures (UUIs) are a vital component of built capital for urban sustainability. However, many cities are now home to a multitude of disused or underutilized UUIs, not least aged purpose-built underground facilities, causing a waste of valu- able underground space resource assets. In the process of urban renewal, adaptive reuse can be an attractive solution to breathe new life into underutilized UUIs, while addressing some of the modern problems of the built environment by an economically feasible means. Nevertheless, there is a prevalent absence in the current literature of the overarching planning and decision-making approaches for an adaptive reuse development of underutilized UUIs. With the intention of addressing this shortfall, this paper first lays out develop- ment strategies, then sets the generic patterns for adaptive reuse of disused or underutilized UUIs. Taking the city of Qingdao, China as a case study, detailed planning and decision-making approaches with the aid of multi-source data and spatial analysis tools are presented. It is anticipated that the findings of this research will assist the adaptive reuse development of UUIs in providing theoretical guidance and empirical evidence, thereby enhancing the role of urban underground space use in contributing to urban revitalization and urban sustainability.

It is inevitable to cut reinforced concrete (RC) appeared in cross passage of city metro by cutting tools when constructing in densely populated area. The previous cutters employed to cut RC are insufficient and easily damaged, so a new polycrystalline diamond compact (PDC) cutter is used to solve this question. Based on the theoretical analysis of cutting mechanism, both circular and tapered PDC cutters with cutting edge angle of 90° and negative front rack angle of 10° are used to cut RC. The peeling and breaking patterns of cutting concrete are proposed, the nodular and grainy chips are the preferred modes in cutting steel bars. The LS-DYNA is employed to investigate the cutting performance in advance. The simulation results show that the average and peak cutting forces increase with the growth of penetration depth, cutting speed, and roundness, and subsequently the recommended penetration depth less than 1.2 mm is obtained to cut RC due to the existence of steel bars. Moreover, the linear cutting platform is adopted to investigate the force ability and damage state of PDC cutters. It is concluded that the cutting force increases abruptly and fluctuates heavily when cutting the coarse aggregates. The patterns occurred in both numerical and experimental results are generally similar. Notably, the steel bar is pulled out and the PDC cutter is damaged at the penetration depth of 0.8 mm, while a good cut occurs at the penetration depth of 0.3 mm. The tapered PDC cutter with a relatively low cutting force is prone to be broken compared with circular PDC cutter. It is suggested that the circular PDC cutter at the penetration depth of 0.3 mm should be used to cut RC in practical engineering.

Fibre-reinforced sand (FRS) is a multiphase and multiscale geo-material, which is widely used in geotechnical engineering as supporting structure of excavation of underground space and reinforcement of foundation of underground structures, and its strength is determined by the properties of the heterogeneous substances of the FRS and their coupling mechanical responses. In order to investigate the influence of fibre characteristics and mechanical properties on the shear strength of the FRS, according to the microscopic interface slip effect generated by the interaction between sand particles and the interaction between these particles and fibre, the material phase of the FRS is divided to conceptualize a micro cell element of the FRS that is capable of reflecting the internal material characteristic information of the FRS. Moreover, based on the coordinated deformation condition between fibres and sand particles at the microscale and the couple stress theory that is capable of effectively describing the discontinuous mechanical responses at the sand-fibre interface, a mesomechanism-based multiscale Mohr-Coulomb shear strength criterion of the FRS is derived, and the yield locus of the FRS is also drawn on the p plane. Furthermore, a series of FRS samples with different fibre content and fibre length were prepared by adopting the freezing method, and consolidated and drained triaxial compression tests were conducted on these samples to validate the proposed multiscale coupled Mohr-Coulomb shear strength criterion. Results show that the multiscale coupled Mohr-Coulomb shear strength criterion is capable of effectively reproducing and predicting the yield strength of the FRS. The yield locus of the FRS extends outwards as fibre content and fibre length increase. The yield stress of the FRS predicted by the proposed multiscale coupled Mohr-Coulomb shear strength criterion is in good agreement with that of the test result.

The technical challenges associated with deep underground space activities have become increasingly significant. Among these challenges, one major concern is the assessment of rockburst risks and the instability of rock masses. Extensive research has been conducted by numerous scholars to mitigate the risks and prevent occurrences of rockburst through various assessment methods. Rockburst incidents commonly occur during the excavation of hard rock in underground environments, posing severe threats to personnel safety, equipment integrity, and operational continuity. Thus, it is crucial to systematically document real cases of rockburst, allowing for a comprehensive understanding of the underlying mechanisms and triggering conditions. This understanding will contribute to the advancement of rockburst prediction and prevention methods. Proper selection of an appropriate rockburst assessment method is a fundamental aspect in underground operations. However, there is a limited number of studies that summarize and compare different prediction and prevention methods of rockburst. This paper aims to address this gap by analyzing global trends using CiteSpace software since 1990. It discusses rockburst classification and characteristics, comprehensively reviews research findings related to rockburst prediction, including empirical, simulation, mathematical modeling, and microseismic monitoring methods. Additionally, the paper presents a compilation of current rockburst prevention measures. Notably, the paper emphasizes the significance of control strategies, which provide key insights into the effective utilization of stored energy within rock. Finally, the paper concludes by suggesting six directions for implementing intelligent management techniques to mitigate hazards during underground operations and reduce the probability of rockburst incidents.

During the initial design phases of complex multi-disciplinary systems such as urban tunnelling, the appraisal of different design alter- natives can ensure optimal designs in terms of costs, construction time, and safety. To enable the evaluation of a large number of design scenarios and to find an optimal solution that minimises impact of tunnelling on existing structures, the design and assessment process must be efficient, yet provide a holistic view of soil-structure interaction effects. This paper proposes an integrated tunnel design tool for the initial design phases to predict the ground settlements induced by tunnelling and building damage using empirical and analytical solutions as well as simulation-based meta models. Furthermore, visualisation of ground settlements and building damage risk is enabled by integrating empirical and analytical models within our Building Information Modelling (BIM) framework for tunnelling. This approach allows for near real-time assessment of structural damage induced by settlements with consideration of soil-structure interaction and non-linear material behaviour. Furthermore, because this approach is implemented on a BIM platform for tunnelling, first, the design can be optimised directly in the design environment, thus eliminating errors in data exchange between designers and computational ana- lysts. Secondly, the effect of tunnelling on existing structures can be effectively visualised within the BIM by producing risk-maps and visualising the scaled deformation field, which allows for a more intuitive understanding of design actions and for collaborative design. Having a fully parametric design model and real-time predictions therefore enables the assessment and visualisation of tunneling-induced damage for large tunnel sections and multiple structures in an effective and computationally efficient way.

As a major element of the transportation network, tunnels are unavoidably threatened by accidental loads such as vehicle bombs and tank truck explosions. The goal of this research is to explore the dynamic characteristics and damage assessment of tunnel structures under contact blast loads. First, three scaled-down reinforced concrete tunnel models were made, and the explosion test and static loading test were carried out successively to evaluate the axial residual bearing capacity, axial displacement and failure mechanism of the tunnel. Secondly, the finite element model is built by utilizing LS-DYNA, and the reliability of the finite element method is confirmed by comparing the data of the explosion test with the static loading test. At the same time, the calculation method for damage coefficient and the classification criteria for damage grade based on axial residual bearing capacity are presented. Then, based on the finite element method, the propagation process of the explosion shock wave in the tunnel and the damage mechanism of the tunnel are investigated. Finally, seven explosion scenarios are developed, the damage degree of these seven tunnels under the blast load is quantitatively analyzed, and further anti-blast design ideas are put forth. The study in this article may give an intended reference for the damage assessment, anti-explosion design and strengthening work of reinforced concrete tunnels.

To investigate the compression-shear behavior of a new circumferential joint based on the sleeve-straight bolt combination type con- nection of large-diameter shield tunnels, a series of full-scale joint experiments was carried out. In the process of the experiment, more attention was paid to the specimen displacement, bolt stress and joint damage mode. On the basis of these experiment phenomena, this study discussed the compression-shear bearing process of the new connector, analyzed the damage mode of the joint structure, and finally evaluated the performance of the new connector. It is found that the bearing process of the joint can be divided into four stages: the transitional stage for overcoming the friction of the concrete, the sleeve bearing stage for the sleeve bearing shear loads alone, the com- bined bearing stage for bearing shear loads by the connector system, and the structural damage stage for structural instability and dam- age. Generally speaking, affected by connector position and hand hole, the positive compression-shear stiffness of the joint is less than the negative compression-shear stiffness, and the positive shear strength of the joint is greater than the negative shear strength. The increase of longitudinal axial force will improve the compression-shear performance of the joint. The relationship between longitudinal axial force and joint stiffness is a logarithmic function. The use of new type of connector can effectively improve the compression-shear stiffness of joints under low shear loads, but the application of straight bolts will lose part of the strength performance.

Although super-large-span tunnels ensure convenient transportation, they face many support challenges. The lack of normative construction guidance and the limited number of reference engineering cases pose a significant challenge to the stability control of super- large-span tunnels. Based on the geological conditions of a super-large-span tunnel (span = 32.17 m) at the bifurcation section of the Shenzhen interchange, this study determined support parameters via theoretical calculation, numerical simulation, and engineering analogy. The support effects of negative Poisson’s ratio (NPR) anchor cables and ordinary anchor cables on super-long-span tunnels were simulated and studied. Further, based on FLAC^3D simulations, the surrounding rock stress field of NPR anchor cables was analyzed under different prestressing conditions, and the mechanism of a long-short combination, high-prestress compensation NPR anchor cable support was revealed. On the basis of numerical simulations, to our knowledge, the three-dimensional (3D) geomechanical model test of the NPR anchor cable and ordinary anchor cable support for super-large-span tunnel excavation is conducted for the first time, revealing the stress evolution law of super-large-span tunnels, deformation and failure characteristics of the surrounding rock, and the changing trend of the anchor cable’s axial force, and verifies that NPR anchor cables with high preloads are suitable for super-large-span tunnel support and have advantages over ordinary anchor cables. This study can provide a reliable theoretical reference for the support design and stability control of the surrounding rock of similar shallow-buried super-large-span tunnels.

With the fact that the main operational parameters of the construction process in mechanized tunneling are currently selected based on monitoring data and engineering experience without exploiting the advantages of computer methods, the focus of this work is to develop a simulation-based real-time assistant system to support the selection of operational parameters. The choice of an appropriate set of these parameters (i.e., the face support pressure, the grouting pressure, and the advance speed) during the operation of tunnel boring machines (TBM) is determined by evaluating different tunneling-induced soil-structure interactions such as the surface settlement, the associated risks on existing structures and the tunnel lining behavior. To evaluate soil-structure behavior, an advanced process-oriented numerical simulation model based on the finite cell method is utilized. To enable the real-time prediction capability of the simulation model for a practical application during the advancement of TBMs, surrogate models based on the Proper Orthogonal Decomposition and Radial Basis Functions (POD-RBF) are adopted. The proposed approach is demonstrated through several synthetic numerical examples inspired by the data of real tunnel projects. The developed methods are integrated into a user-friendly application called SMART to serve as a support platform for tunnel engineers at construction sites. Corresponding to each user adjustment of the input parameters, i.e., each TBM driving scenario, approximately two million outputs of soil-structure interactions are quickly predicted and visualized in seconds, which can provide the site engineers with a rough estimation of the impacts of the chosen scenario on structural responses of the tunnel and above ground structures.

This paper proposed a two-way coupled computational fluid dynamics (CFD) and discrete element method (DEM) approach to analyze the evolution of clogging in slurry shield tunneling quantitatively. The interactions between clay particles and slurry were considered by exchanging three interaction forces, including buoyancy force, pressure gradient force, and drag force. The CFD-DEM coupling approach was first benchmarked by comparing cutterhead torque and total thrust with field monitored data of a practical slurry shield tunnel project. The evolution process of the particle phase and the fluid phase over time was presented. The results indicated that fewer than 70% of the particles can be washed away in time by the circulating slurry. About 9% of the particles adhered to the submerged wall, resulting in increased cutterhead torque and thrust. Through parametric analysis, the influence of the shield driving parameters on the clay clogging behavior is further explored. The time history of cutterhead torque or thrust can be used as a criterion for judging whether clogging has occurred. Additionally, a new assessment method of clogging risk and an optimization strategy of driving parameters were proposed, which were intended to provide some guidance for similar projects.

The surcharge load at the ground surface inevitably breaks the original equilibrium state between the underneath tunnel and the surrounding soil, which will impact the service performance of a subway tunnel. This paper presents a novel semi-analytical approach for assessing the time-dependent, longitudinal responses of a subway tunnel in soft soil strata induced by the surcharge load. The solution is developed based on the framework of the classical ‘‘two-stage method” but innovatively incorporates the effects of ground stratification, the consolidation process, and the longitudinal stiffness reduction of the lining. Biot’s poroelastic theory in conjunction with the Laplace- Fourier transform technique is selected to model the deformation of the stratified ground, while the Timoshenko beam on a Pasternak foundation is employed to model the mechanical responses of the tunnel. The proposed semi-analytical solution is validated not only by comparison with benchmark solutions and a finite element model, but also by predicting a well-documented field measurement. Parametric analyses are conducted to investigate the effects of the elastic modulus and the permeability coefficient of the stratified ground on the longitudinal responses of the tunnel. It is expected that the proposed solution can serve as a useful tool for evaluating the effects of the surcharge load on the longitudinal responses of a subway tunnel.

Legal boundaries are used for delineating the spatial extent of ownership property’s spaces. In underground environments, these boundaries are defined by referencing physical objects, surveying measurements, or projections. However, there is a gap in connecting and managing these boundaries and underground legal spaces, due to a lack of data model. A 3D data model supporting underground land administration (ULA) should define and model these boundaries and the relationships between them and underground ownership spaces. Prominent 3D data models can be enriched to model underground legal boundaries. This research aims to propose a new taxonomy of underground legal boundaries and model them by extending CityGML, which is a widely used 3D data model in the geospatial science domain. We developed, implemented, and tested the model for different types of underground legal boundaries. The implemented prototype showcased the potential benefits of CityGML for managing underground legal boundaries in 3D. The proposed 3D underground model can be used to address current challenges associated with communicating and managing legal boundaries in underground environments. While this data model was specifically developed for Victoria, Australia, the proposed model and approach can be used and replicated in other jurisdictions by adjusting the data requirements for underground legal boundaries.

The localised leakage in shield tunnels that mainly occurs at segment joints may induce other defects, which threatens operational safety. To obtain a universal solution for the sealant performance of gasketed joints, we proposed a novel analytical model based on the multiscale contact and percolation theories, in which the obtained percolation pressure and interfacial separation can be utilized to derive the critical water leakage pressure and leakage rate. The evolutionary process of leakage was divided into three stages (i.e., the percolation, leakage and breakdown), which explicitly reveal the progressive hydraulic deterioration of gasketed joints. The gaskets still own partial waterproof capacity until the end of the leakage stage due to the remaining contact pressure at surface asperities. The proposed model was first verified by several sets of experimental data, based on which the determination of three key model parameters (i.e., self-sealing slope, sealing coefficient, and expel pressure) were discussed in detail. The parametric study indicates that the waterproof capacity is significantly affected by the joint opening, offset, and the surface roughness of the gaskets. The variation in waterproof capacity with joint opening is mainly due to the nonlinearity of the gasket’s modulus and self-sealing slope. The increase in joint offset can result in a lower waterproof capacity as well as a larger leakage rate. Gasket’s surface roughness affects the percolation pressure and interfacial separation, which contributes to the long-term sealant performance.

Cities play a vital role in social development, which contribute to more than 70% of global carbon emission. Low-carbon city construction and decarbonization of the energy sector are the critical strategies to cope with the increasingly serious climate change problems, and low-carbon technologies have attracted extensive attention. However, the potential of such technologies to reduce carbon emissions is constrained by various factors, such as space, operational environment, and safety concerns. As an essential territorial natural resource, underground space can provide large-scale and stable space support for existing low-carbon technologies. Integrating underground space and low-carbon technologies could be a promising approach towards carbon neutrality, and hence, warrants further exploration. First, a comprehensive review of the existing low-carbon technologies including the technical bottlenecks is presented. Second, the features of underground space and its low carbon potential are summarized. Moreover, a framework for the underground space based integrated energy system is proposed, including system configuration, operational mechanisms, and the resulting benefits. Finally, the research prospect and key challenges required to be settled are highlighted.

For the project of pipe jacking in cohesionless soil, it is key to determine the vertical load on jacked pipe so as to predict the jacking force accurately. In this paper, a new parabolic soil arching model was proposed to calculate the vertical load on jacked pipe. This proposed analytical model was composed of parabolic soil arching zone, parabola-typed collapse zone and friction arch zone. Combined with existing literature, the key parameters (i.e., height of parabolic soil arching, horizontal pressure coefficient and width and height of friction arch) were determined. In addition, considering that the trajectory of major stress is parabola, the formula of horizontal pressure coefficient was deduced in the friction arch. The parabolic soil arching zone is assumed as a three-hinged arch with reasonable arch axis, and the formula of load transfer was derived considering the transition effect of parabolic soil arching. The results of experiment, theoretical models and numerical model were adopted to verify the proposed analytical model. Finally, the influence of the key parameters on the vertical load on jacked pipe were also discussed in detail. This work provides a meaningful reference for evaluating the vertical load on jacked pipe for design of pipe jacking.

Three-dimensional (3D) roughness of discontinuity affects the quality of the rock mass, but 3D roughness is hard to be measured due to that the discontinuity is invisible in the engineering. Two-dimensional (2D) roughness can be calculated from the visible traces, but it is difficult to obtain enough quantity of the traces to directly derive 3D roughness during the tunnel excavation. In this study, a new method using Bayesian theory is proposed to derive 3D roughness from the low quantity of 2D roughness samples. For more accurately calculating 3D roughness, a new regression formula of 2D roughness is established firstly based on wavelet analysis. The new JRC_3D prediction model based on Bayesian theory is then developed, and Markov chain Monte Carlo (MCMC) sampling is adopted to process JRC_3D prediction model. The discontinuity sample collected from the literature is used to verify the proposed method. Twenty groups with the sampling size of 2, 3, 4, and 5 of each group are randomly sampled from JRC_2D values of 170 profiles of the discontinuity, respectively. The research results indicate that 100%, 90%, 85%, and 60% predicting JRC_3D of the sample groups corresponding to the sampling size of 5, 4, 3, and 2 fall into the tolerance interval [JRC_true-1, JRC_true + 1]. It is validated that the sampling size of 5 is enough for predicting JRC_3D. The sensitivities of sampling results are then analyzed on the influencing factors, which are the correlation function, the prior distribution, and the prior information. The discontinuity across the excavation face at ZK78 + 67.5 of Daxiagu tunnel is taken as the tunnel engineering application, and the results further verify that the predicting JRC_3D with the sampling size of 5 is generally in good agreement with JRC_3D true values.

In the present work, important aspects of time-dependent nonlinear 3D finite element (FE) models for deep tunnel advance by the New Austrian Tunneling Method(NATM), characterized by repeated sequences of excavation, securing, and idle periods, are discussed on the example of a 3D finite element model of a stretch of the Brenner Base Tunnel, which is currently constructed between Austria and Italy. Nonlinear material models are utilized for representing the surrounding rock mass and the shotcrete shell. Based on the finite element model, strategies for the efficient implementation into a parallel distributed memory numerical code are proposed. They are essential to achieve reasonable computation times for numerical simulations of tunneling based on large 3D FE models. In particular, the implementation of the construction procedure, parallel computing and communication specific details, and efficient linear solvers for the global equation system within the incremental-iterative Newton-Raphson scheme are addressed. Furthermore, possible extensions of the material models for rock mass and shotcrete, used in the 3D FE model, are presented. They concern (i) a gradient-enhanced model for transversely isotropic rock and rock mass, taking into account hardening and softening behavior and (ii) the extension of the shotcrete model to nonlinear creep and damage due to creep. The possible benefits of the model extensions in numerical simulations of tunneling by the NATM are discussed.