Twin Tunnels Research Articles

The pioneer of intelligent and sustainable construction in tunnel shotcrete applications: a comprehensive experimental and numerical study on a self-sensing and self-heating green cement-based composite

In this study, a self-sensing and self-heating natural fibre-reinforced cementitious composite for the shotcrete technique was developed using Kenaf fibres. For this purpose, a series of Kenaf fibre concentrations were subjected to initial chemical treatment, followed by integration into the cement-based composite containing hybrid carbon nanotubes (CNT) and graphene nanoplatelets (GNP). The investigation encompassed an examination of mechanical, microstructural, sensing, and joule heating performances of the environmentally friendly shotcrete mixture, with subsequent comparisons drawn against a counterpart blend featuring a conventionally synthesized polypropylene (PP) fibre. Following the experimental phase, a comprehensive 3D nonlinear finite difference (3D NLFD) model of an urban twin road tunnel, completed with all relevant components, was meticulously formulated using the FLAC3D (fast lagrangian analysis of continua in 3 dimensions) code. This model was subjected to rigorous validation procedures. The performances of this green shotcrete mixture as the lining of the inner shell of the tunnel were assessed comparatively using this 3D numerical model under static and dynamic loading. The twin tunnel was subjected to a harmonic seismic load as a dynamic load with a duration of 15 s. The laboratory findings showed a reduction in the composite sensing and heating potentials in both cases of Kenaf and PP fibre reinforcement. Incorporating a specific quantity of fibre yields a substantial enhancement in both the mechanical characteristics and microstructural attributes of the composite. An analysis of digital image correlation demonstrated that Kenaf fibres were highly effective in controlling cracks in cement-based composites. Furthermore, based on the static and dynamic 3DNLFD analysis, this green cement-based composite demonstrated its potential for shotcrete applications as the lining of the inner shell of the tunnel. This study opens an appropriate perspective on the extensive and competent contribution of natural fibres for multifunctional sustainable, reliable and affordable cement-based composite developments for today’s world.

Engineering characteristics and classification based on JSCE in portal zones of Tunnel A, Yogyakarta - Bawen toll road, Magelang District, Central Java Province

The Yogyakarta - Bawen Twin Tunnels emerge as an environmentally conscious solution for Toll Road Phase 5 (STA 6+300 to STA 27+640), addressing the ecological impact of open-cut excavation, which demands a staggering 1,209,056 m3. Open-cut excavation not only incurs substantial operational costs, encompassing disposal and treatment, but also poses threats like groundwater loss and erosion-induced landslides. The twin tunnels mitigate these concerns by limiting excavation volume to a mere 1/8, averting substantial costs and ecological damage. Challenges persist, particularly in the portal zones of Tunnel A, characterized by a shallow overburden and exposure to weathering. The Japan Society of Civil Engineers (JSCE) Method proves instrumental in assessing ground quality in these zones, considering factors such as competence, unit weight, unconfined compressive strength, depth of cover, elastic wave velocity, boring core condition, and geological characteristics. The analysis reveals a ground quality classification of E for the portal zone in Tunnel A, emphasizing the necessity for a meticulous design approach that incorporates analytical methodologies alongside empirical considerations. Notably, the unconfined compressive strength ranges from 32.89 to 472.88 kPa, and the elastic wave velocity spans 402 to 2000 meters/sec, reinforcing the imperative for a comprehensive and analytically informed design for excavation and support systems.

The Effect of GSI and mi on the Stability of 3D Twin Tunnel in Limestone

The Generalised Hoek-Brown (GHB) failure criterion is one of the most used criteria to study the behaviour of the rocks; affected parameters of the Hoek-Brown equation are Geological Strength Index (GSI), intact rock constant (mi), and Disturbance factor (D). GSI is one of the rock classification systems used to evaluate jointed rocks. In light of this equation, this paper studies the stability of unsupported twin tunnels in a weak rock by changing the mentioned parameters (GSI, mi) to find the relation between the stability and these parameters under different distances between the centres of the tunnels (L). The tunnels have a circular cross-section with a diameter (B), and they have been modelled in three dimensions using Rocscience software package (RS3). The results showed that the stability of the tunnels, which was represented by the strength reduction factor (SRF), increased as a result of increasing L/B or GSI in the studied range; for mi , the modelling results showed that the SRF value increased while mi value was increased.

Impact of Excavation Phase Shift on Mechanized Twin Tunnels in Soft Ground: A 3D Numerical Study

Impact of Excavation Phase Shift on Mechanized Twin Tunnels in Soft Ground: A 3D Numerical Study

Prediction method of longitudinal surface settlement caused by double shield tunnelling based on deep learning

The deep learning method faces the challenges of small sample data and high dimensional shield operational parameters in predicting the longitudinal surface settlement caused by shield excavation. In this study, various optimization algorithms were compared, and the slime mould algorithm (SMA) was optimally chosen to optimize the hyperparameters of random forest (RF), and SMA-RF was used for dimensionality reduction and feature contribution analysis. A double-input deep neural network (D-DNN) framework was proposed for the prediction of surface settlement, which considers the influence of twin tunnels and effectively increases the high-fidelity data in the database. The results show that SMA performs best among various optimization algorithms; employing features that have a cumulative contribution value exceeding 90% as input can result in high prediction accuracy; there is significant uncertainty in the feature contribution analysis for small sample data; the reduced shield running parameters show a strong nonlinear relationship with surface settlement; compared with S-DNN, D-DNN takes into account the excavation of twin tunnels and expands the database capacity by more than 1.5 times, with an average increase of 27.85% in the R2 and an average decrease of 53.2% in the MAE.

Investigation on Response of Site of Typical Soil–Rock Composite Strata in Changchun Induced by Shield Construction of Parallel Twin Tunnels

Underground engineering construction will inevitably change the stress state of surrounding strata, which will force a negative impact on the surrounding environment, even leading to the large deformation and damage of some adjacent structures. With a focus on the deformation of a typical soil–rock composite stratum site in the construction of Changchun Metro, relying on the shield construction of a parallel twin tunnel project between Northeast Normal University Station and Gong-Nong Square Station, which belongs to the Changchun Metro Line 1, the site deformation characteristics during the shield driving process of parallel twin tunnels were studied. Based on the data obtained from field monitoring and numerical simulation, ground settlement in shield driving was analyzed, the settlement trough was studied with the Peck formula, and the action of shield driving on the adjacent tunnel was discussed. Moreover, the influence range of shield driving was suggested, and the interaction between the twin tunnels with different axis spacings in shield driving was discussed. Some regular results obtained can provide support through data for similar projects in Changchun, China.

Analytical solution of Tunnel-Soil-Tunnel (TST) interaction under seismic excitation

ABSTRACT This research proposes the analytical formulations for the vertically aligned twin tunnels under the sinusoidal form of seismic excitation in the case of the damped free vibration. The analytical formulae are derived to calculate the interactive tunnel moment, tunnel shear force and soil pressure for the transverse horizontal shear (SH), vertical shear (SV) and body (P) waves. For the derivation of the analytical formulations, the twin tunnels are assumed as beam elements connected by the linear elastic springs. The tunnel-soil-tunnel (TST) interaction model is verified by the previous analytical solution and numerical analysis of the case studies. The ranges of the difference in results between the present research and the previous analytical solution are found to be (3.8 ~ 8.1) %, (6.73 ~ 10.95) % and (2.3 ~ 11.79) % in the case of the SH, SV and P waves, respectively. These differences may represent good agreement about verifications.

Three-dimensional hydro-mechanical coupling numerical simulation of shield-driven cross-river twin tunnels: A case study

With the rapid development of urban underground space, the construction of shield-driven cross-river twin tunnels is increasing, and the complex hydro-mechanical coupling effects and twin-tunnel interactions bring huge construction risks to such projects, which have attracted more and more attention. This study aims to understand the excavation effects induced by shield driving of cross-river twin tunnels through numerical simulation. A refined three-dimensional numerical model based on the fully coupled hydro-mechanical theory is established. The model considers the main components of the slurry pressure balance shield (SPBS) machine, including support force, jacking thrust, grouting pressure, shield-rock interaction and lining-grouting interaction, as well as the detailed construction process. The purpose is to examine the excavation effects during construction, including rock deformation around tunnels, the change in pore pressure, and the response of the lining. The results show the influence range of twin-tunnel excavation on rock deformation and pore pressure, as well as the modes of lining response. In addition, this study also systematically investigates the effects of water level fluctuation and burial depth on twin-tunnel excavation. The results indicate that the increase of water level or burial depth will enhance the excavation effects and strengthen the twin-tunnel interactions. These results provide useful insights for estimating the construction impact range and degree of twin tunnels, and serve as basic references for the design of cross-river twin tunnels.

Twin tunnels critical underpass during Sofia metro line 3 extension

Twin tunnels critical underpass during Sofia metro line 3 extension

Dimensionless analysis of scattering around twin tunnels subjected to P wave using FESCAM approach

Dimensionless analysis of scattering around twin tunnels subjected to P wave using FESCAM approach

The effects of excavating twin tunnels during cyclic loading on the progressive settlement of existing footing

Tunnels may be constructed in a pair undercrossing existing geotechnical structures exposed to cyclic loading. Such construction changes the stress state in the ground in different ways regarding the tunnelling sequence and would lead to large settlement or even failure to those structures under cyclic loading. Large physical model tests were carried out to examine the impact of excavating twin tunnels during cyclic loading on the progressive settlement of footings. The vertical soil stress, footing settlement and ground deformation were analysed regarding different construction sequences and spacings between twin tunnels. The results indicate that previous cyclic loading history affects the alteration of soil stress caused by tunnelling activity. Compared with excavating twin tunnels successively, excavating the tunnels in sequence leads to greater settlement caused by the subsequent cyclic loading. The change in the relative density of soil is invalid to explain the enlargement of the settlement. Finite element analysis was performed to investigate the mechanism of the effects of excavating twin tunnels during cyclic loading on the footing settlement. It was found that the increase of footing settlement in the subsequent cyclic loading and the greater settlement in the sequential tunnelling case are attributed to the greater stress ratio (q/p) in the ground.

Twin-tunnelling: Case studies in clay

New developments in the theory and practice of tunnel construction are essential for the industry to progress but it is the relationship between these two areas that is equally as important. Tunnelling practice has greatly benefited from laboratory research; specifically, centrifuge modelling linked with field measurements. The wide body of work on the construction of single tunnels has led to the identification of parameters and techniques that are widely accepted for predicting and assessing the magnitude and extent of tunnelling ground movements. However, the usage of twin tunnels in urban areas for transportation purposes have increased and better understanding on the associated ground displacements are required. This paper firstly provides background to ground displacements due to single tunnel, twin tunnel constructions and common prediction methods used in practice. Then, it introduces recent technological advancements in centrifuge modelling, applied to the complex geotechnical events of twin-tunnelling, that has led to further insight. The tunnelling induced ground displacements obtained from twenty four case studies in clay around the world and eighteen centrifuge tests are presented for further analyses. From that, a comparison between the recent theories of proximity-dependent tunnelling-induced ground movements with case histories has been carried out to establish their validity and limitations. Published field measurements have been reanalysed taking into account newly discovered relationships between the tunnels’ proximity and the magnitude and extent of ground movements, reflected via volume loss and the settlement trough width, respectively. The applicability to field measurements of the additional volume loss prediction method (derived from consideration of the experiment work) for tunnelling in clay is assessed.

Damages of highway tunnels during 2022 Luding earthquake (Mw = 6.6)

On 5 September 2022, an Mw = 6.6 earthquake hit the Luding area, Sichuan Province, China, leading to 93 deaths, 25 disappearances, and great economic loss. The earthquake caused a series of geologic hazards and severe damage to infrastructures, such as tunnels, bridges, houses, and roads. In this study, a field survey was conducted for the twin tunnels along the Luding-Shimian highway after the earthquake. The highway was close to the epicenter, which was built along the Daduhe fault. Comprehensive data on tunnels along the highway, such as damage characteristics, geological conditions, conditions behind the tunnels, and design documents, were collected. The field investigation found that three tunnels were damaged due to seismic shaking. Tunnel damage, such as cracks, spalling, and leakage, was observed. Based on the compiled data, a preliminary analysis was performed for the possible mechanisms of damage to the tunnels. The damage was related to the old landslide mass, fractured zone, invert setup, and direction of tunnel alignment.

Elastoplastic solutions for deep-buried twin tunnels with arbitrary shapes and various arrangements under biaxial in-situ stress field based on Mohr-Coulomb and generalized Hoek-Brown criteria

Theoretical solutions for elastoplastic analysis of deep-buried twin tunnels with arbitrary shapes and various arrangements are developed under biaxial in-situ stress field based on Mohr-coulomb (M–C) and generalized Hoek-Brown (G-H-B) criteria. The boundary stress transformation formulas adapted for arbitrary stress conditions on non-circular tunnel wall are provided in terms of conformal transformations. Regarding the plastic analysis, analytical expressions for stress characteristic relationships along slip lines under generalized Hoek-Brown criterion are derived. Subsequently, the semi-analytical solutions for plastic stresses of rock surrounding arbitrary-shaped tunnels are constructed based on Mohr-Coulomb and generalized Hoek-Brown criteria applying conformal mapping technique, slip-line method and finite difference-numerical iterative approach. On the basis of the discrete plastic stresses, interpolation functions are generated according to three-dimensional linear interpolation technique. And then, solutions for elastic stress function and plastic radius of twin tunnels with various arrangements are developed with improved mapping functions and newly defined fitness functions through differential evolution method. The accuracy of the semi-analytical solutions is verified by the numerical simulation. Meanwhile, the proposed solutions have the advantages of meshless characteristic, better convergence and higher computing efficiency comparing with the numerical simulation. From the point of engineering, the developed elastoplastic solutions can provide theoretical supports for the stress analysis, plastic radius estimation, safety clearances optimizations of deep-buried twin tunnels.

Treatment measures for the creep–slip phase of landslides induced by twin tunnels

Tunnel excavation in geologically challenging areas can lead to slope instability and consequent landslides, which pose a serious threat to the integrity of the tunnel lining. To address this issue, a study was conducted to investigate the stability of the tunnel–landslide system using the finite-difference method (FDM) based on the Hanshankou tunnel of the Shaoguan–Xinfeng expressway in Guangdong province, China. A plane-strain model was used to examine the effect of various treatment measures on the system, and the strength reduction (incremental) method was employed to determine the range of initial slope safety factors applicable to different treatment measures, with the maximum shear strain increment serving as the criterion. The ‘anti-slip pile + anchor frame beam’ reinforcement system was found to be the most effective solution, reducing daily deformation by 60.1% after implementation. The results indicated that the pile–anchor reinforcement system can significantly mitigate landslide creep, and the corresponding treatment measures can be categorised based on the critical slope safety factor under different conditions.

Experimental and Numerical Studies of a Shield Twin Tunnel Undercrossing the Existing High-Speed Railway Tunnel

Experimental and Numerical Studies of a Shield Twin Tunnel Undercrossing the Existing High-Speed Railway Tunnel

Effect of dynamic loading orientation on fracture properties of surrounding rocks in twin tunnels

For expedited transportation, vehicular tunnels are often designed as two adjacent tunnels, which frequently experience dynamic stress waves from various orientations during blasting excavation. To analyze the impact of dynamic loading orientation on the stability of the twin-tunnel, a split Hopkinson pressure bar (SHPB) apparatus was used to conduct a dynamic test on the twin-tunnel specimens. The two tunnels were rotated around the specimen’s center to consider the effect of dynamic loading orientation. LS-DYNA software was used for numerical simulation to reveal the failure properties and stress wave propagation law of the twin-tunnel specimens. The findings indicate that, for a twin-tunnel exposed to a dynamic load from different orientations, the crack initiation position appears most often at the tunnel corner, tunnel spandrel, and tunnel floor. As the impact direction is created by a certain angle (30°, 45°, 60°, 120°, 135°, and 150°), the fractures are produced in the middle of the line between the left tunnel corner and the right tunnel spandrel. As the impact loading angle (α) is 90°, the tunnel sustains minimal damage, and only tensile fractures form in the surrounding rocks. The orientation of the impact load could change the stress distribution in the twin-tunnel, and major fractures are more likely to form in areas where the tensile stress is concentrated.

Simulation of Surface Settlement Induced by Parallel Mechanised Tunnelling

Mechanised tunnelling is extensively utilised for twin tunnel construction, particularly in urban areas. A common challenge encountered during this construction method is the occurrence of surface settlement (SS) induced by tunnelling activities. The integrity of nearby structures can be compromised by SS, making it imperative to accurately quantify and mitigate this phenomenon. Several methods for determining SS exist, including empirical formulas and laboratory studies. However, these methods are often constrained by specific soil types and are time-consuming. Moreover, crucial parameters such as tunnel operational factors and construction stages are often omitted from empirical formulas. Given these limitations, this paper aims to address these challenges by employing 3D numerical analysis to simulate tunnelling-induced SS in twin tunnels. This approach takes into account tunnel geometry, construction sequencing, soil properties, and tunnelling operational factors. By incorporating data from in-situ and laboratory tests conducted on the ground, engineering soil parameters are established as inputs for the numerical analysis. The simulated SS results obtained from the 3D numerical analysis are compared with field measurements of SS taken from available ground surface settlement markers. The transverse SS pattern derived from the numerical analysis closely mirrors the field measurements. Additionally, SS values above the first and second tunnels are compared with field measurements, resulting in coefficient of determination (R2) values of 0.94 and 0.96, respectively. The utilisation of the 3D numerical modelling approach enables the customizable mitigation strategies for managing the SS with project-specific parameters such as tunnel geometry, geotechnical engineering factors, and tunnelling operational variables. This will help plan and construct more sustainable tunnels with minimal effects on the ground and residential areas.

Assessment of twin tunnelling induced settlement and load transfer mechanism of a single pile in dry sand

This study conducted both three-dimensional physical model tests and numerical back-analyses to examine the performance of a single pile subjected to twin tunnelling beneath the pile toe in dry sand. Moreover, numerical parametric analyses were carried out to assess the impact of working load level and tunnel volume loss on pile behaviour. The findings revealed that the first tunnelling induced a 1.9% dp (pile diameter) settlement in the pile when the pile toe was 0.5 D (tunnel diameter) above the twin tunnels, which had a 1.0% volume loss. The settlement was accompanied by an upward load transfer mechanism. The second tunnelling had a reduced impact and induced only 76% of the settlement caused by the first tunnelling. The study also showed that tunnelling-induced shearing behaviours weakened beneath the pile toe with a decrease in working load, resulting in reduced pile head settlement. Moreover, the computed pile settlement increased by 178% when the tunnel volume loss increased from 0.5% to 2%. The findings of this study offer valuable data for the validation and calibration of numerical models. In addition, the outcome from this study provides useful insights into the prediction of the pile-soil-tunnel interaction when subjected to twin tunnelling.

MT‐InSAR monitoring for tunnel induced settlements in urban area

AbstractSatellite Interferometric Synthetic Aperture Radar (InSAR) is an accredited technology used in many fields in the last decades, but represents a relatively new technology for civil infrastructures monitoring. It allows to measure displacement along the line of sight (LOS) of the sensor with a millimetric precision. This study was conducted to show the potential of SAR sensors, mounted on satellite platforms, in detecting displacements induced by the excavations of tunnels in urban areas. Advances in remote sensing, such as the development of Multi‐Temporal InSAR algorithms, have overcome the limit of InSAR due to spatial‐temporal decorrelation of the phase measurement, thus improving the precision of the outcomes. Here the COSMO‐SkyMed satellite constellation acquired data over a small area in the city of Naples, affected by the excavation of twin tunnels. Data were processed with the SARPROZ software, while tunnel induced settlement were predicted with empirical methods. To allow comparison, displacements along LOS were projected in the vertical plane. Results indicate a good agreement between the monitored data and the predicted profile of settlement, further confirming the potential of MT‐InSAR in detecting displacements induced by tunneling excavation in urbanized area.