Tunnel Structure Research Articles

The effect of soil conditions on the dynamic response of shield tunnels under train‐induced vibration loads

In this article, the influence of soil condition on the dynamic response of a tunnel and the surrounding soil was studied by both experimental model tests and numerical simulations. We tested a 1/20‐scale tunnel model with three different soil conditions: upper soft soil and lower hard soil, homogeneous soft soil and homogeneous hard soil. We also applied dynamic loads, sweep loads and train loads on the model tunnel for time domain and frequency domain analysis. The experimental and numerical results revealed that the interface between the soft and hard soil strata has an obvious amplification effect on the vibration wave. With the propagation of the vibration wave to the surface, the damping effect of the soil above the tunnel becomes the main factor affecting the dynamic response of soil. The internal force response of the tunnel structure is for the most part concentrated in the section under the excitation load, which is mainly affected by the soil properties beneath the tunnel.

Oxygen vacancy–rich K-Mn3O4@CeO2 catalyst for efficient oxidation degradation of formaldehyde at near room temperature

Synthesis of catalysts with high catalytic degradation activity for formaldehyde (HCHO) at room temperature is highly desirable for indoor air quality control. Herein, a novel K-Mn3O4@CeO2 catalyst with excellent catalytic oxidation activity toward HCHO at near room temperature was reported. In particular, the K addition in K-Mn3O4@CeO2 considerably enhanced the oxidation activity, and importantly, 99.3 % conversion of 10 mL of a 40 mg/L HCHO solution at 30 °C for 14 h was achieved, with simultaneous strong cycling stability. Moreover, the addition of K species considerably influenced the chemical valence state of Mn from +4 (ε-MnO2) to +8/3 (Mn3O4) on the surface of CeO2, which obviously changed the tunnel structure and the number of oxygen vacancies. One part of K species is uniformly dispersed on K-Mn3O4@CeO2, and the other part exists in the tunnel structure of Mn3O4@CeO2, which is mainly used to balance the negative charge of the tunnel and prevent collapse of the structure, providing enough active sites for the catalytic oxidation of HCHO. We observed a phase transition from tunneled KMnO2 to Mn3O4 to tunneled MnO2 with the decreasing K+ content, in which K-Mn3O4@CeO2 exhibited higher HCHO oxidation activity. In addition, K-Mn3O4@CeO2 exhibited lower oxygen vacancy formation and HCHO adsorption energies in aqueous solution based on density functional theory calculations. This is because the K species provide more active oxygen species and richer oxygen vacancies on the surface of K-Mn3O4@CeO2, promote the mobility of lattice oxygen and the room-temperature reduction properties of oxygen species, and enhance the ability of the catalyst to replenish the consumed oxygen species. Finally, a possible HCHO catalytic oxidation pathway on the surface of K-Mn3O4@CeO2 catalyst is proposed.

Numerical study on dynamic response of a novel ribbed thin-walled UHPC box-type utility tunnel under gas explosion

At present, RC utility tunnels are widely used in urban utility tunnels. As a typical confined space, the complex load effect generated by the internal gas explosion of the gas tank of utility tunnel may lead to local damage or overall destruction of the structure of RC utility tunnel. Therefore, it is an important topic to improve the anti-explosion capability of the utility tunnel and ensure the normal operation of the utility tunnel after gas explosion. UHPC structure is considered to have excellent anti-explosion performance, so a ribbed thin-walled UHPC utility tunnel structure was proposed, which improved the overall stiffness and anti-explosion performance of the UHPC utility tunnel through the ribbed section. In view of the shortcomings of fluid-solid coupling method in gas simulation, Computational Fluid Dynamics (CFD) was used to calculate the overpressure distribution after gas explosion in UHPC utility tunnel. The accuracy of UHPC constitutive model and prestress simulation method was verified by testing results from the gas explosion on unbonded prestressed UHPC slab. The gas explosion damage mechanism of ribbed thin-walled UHPC utility tunnel, UHPC-NC combined utility tunnel and RC utility tunnel were comparatively analyzed. And the pre-fabricated stiffener height, UHPC slab thickness and UHPC strength were investigated on the anti-explosion performance of ribbed thin-walled UHPC utility tunnel against gas explosion. It is found that the UHPC strength needs to be enhanced dramatically to improve the blast resistance. The anti-explosion capability of utility tunnel can be effectively increased by increasing the rib height or increasing the thickness of the UHPC utility tunnel structure, and the damage pattern of the utility tunnel can also be changed from flexure-shear failure to bending failure. The results of the study can provide a reference for the damage analysis and anti-explosion design of ribbed thin-walled UHPC utility tunnels.

Experimental investigation on the mechanical properties and failure mechanism of key joints in a new-type prefabricated pile-wall composite structure for the open-cut tunnel

To improve the failure resistance of the lining and make use of the retaining structure, this paper proposed a novel method of adding the key joints to connect the lining with the retaining structure. Usually, the joint is the weak point of the whole structure. The failure mechanism of key joints significantly influences the design and safety of the prefabricated structure. In this study, full-scale loading tests were conducted on three types of key joints: sleeve joint, spiral stirrup joint, and U-shaped rebar joint. The joint deformation, failure mechanism, concrete strain, and reinforcement strain are investigated. The results demonstrated that the deformation and failure process of the key joints can be divided into four stages. The flexural-shear failure caused by the joint opening and the sliding of lining is considered as the main failure mode of the key joints. The U-shaped rebar joint exhibited the best mechanical performance. Furthermore, the finite element modes were created to analyze the influence of axial force and the reinforcement diameter. Combining the test and numerical analysis results, the failure mechanism was revealed. In addition, the joints’ loading-carrying capacity was increased with the increase of axial force due to the axial force limiting the joint opening. The research results provide a theoretical basis and reference for the new-type prefabricated pile-wall composite structure (PPCS).

Study on crack law of shield segment under load variation based on XFEM

PurposeThe occurrence of segment cracks caused by load changes in shield tunnels would affect the safety of the tunnel structure. To this end, a three-dimensional fine shield tunnel segment model based on the extended finite element method (XFEM) is established.Design/methodology/approachThe cracking law of shield segment cracks is studied in two forms: overloading and unloading. The relationship between crack length, width and depth and transverse convergence and deformation is analyzed.FindingsThe results show that the cracks in shield tunnels mainly occur on the outer side of the arch waist and the inner side of the crown and bottom. Under overloading and unloading conditions, the length, width and depth of cracks increase non-linearly as the transverse convergence deformation increases. Under the same convergent deformation, the deeper the buried depth, the smaller the crack length, width and depth. Meanwhile, under overloading conditions, the influence of buried depth on the width and depth of cracks is more significant. In terms of crack width and depth, unloading conditions are more dangerous than overloading conditions.Originality/valueThe findings have a guiding effect for the management of cracks in shield tunnels during operation.

Study on the Stress and Deformation of Surrounding Rock and Support Structure of Super Large Section Tunnels Based on Different Excavation Methods

Study on the Stress and Deformation of Surrounding Rock and Support Structure of Super Large Section Tunnels Based on Different Excavation Methods

Novel V2O3@N-C cathode for superior aqueous zinc-ion batteries via melamine foam templating

Aqueous zinc-ion batteries (AZIBs) are increasingly garnering attention due to their inherent safety features and the economic benefits of using metallic zinc. Among the promising cathode materials for AZIBs, V2O3-based compounds are extensively studied because of their unique tunnel structure and high energy density. However, the broader application of V2O3-based materials is hindered by several challenges, including sluggish reaction kinetics, poor cycling stability, and the lack of effective methods for large-scale synthesis. In response to these limitations, this study utilizes melamine foam as a self-sacrificing template to develop a V2O3@N-C cathode that aims to enhance the performance of aqueous zinc-ion batteries. The resulting cathode benefits from the uniform dispersion of V2O3 nanoparticles and a trace carbon-coated structure enriched with oxygen vacancies, yielding significant reversible capacity (569.62 mA h g−1 at 0.5 A g−1 and 411.63 mA h g−1 at 20 A g−1) and superior cycling stability (369.66 mA h g−1 after 3200 cycles at 10 A g−1). Additionally, ex-situ characterization techniques have been employed to thoroughly investigate the zinc storage mechanism, offering novel insights for the development of high-performance cathode materials for AZIBs.

Study on the stressing state features of basalt fibre concrete lining structure under sulphate erosion

Basalt fibre (BF) is an environmentally friendly material with excellent corrosion resistance. When tunnels cross gypsum rock strata, the gypsum rock will dissolve sulphate and erode the supporting structure, thus affecting the safe operation of the tunnels in the long term. Adding BF to the supporting structure of gypsum rock tunnels can improve its resistance to sulphate erosion. This paper took Wuzhishan Tunnel as a case, and first determined the sulphate concentration of the gypsum rock stratigraphic environment at the site; then, analysed the change of mechanical properties of basalt fibre concrete (BFC) before and after sulphate erosion by mechanical tests; finally, examined the deformation and force characteristics of the BFC secondary lining structure by numerical simulation. The results showed that the bridging effect of BF fibres and the stable spatial network structure formed inside the concrete enhanced the mechanical properties of BFC and its ability to resist sulphate erosion. However, due to the agglomeration effect of BF fibres, too much BF would reduce the mechanical properties and erosion resistance of BFC. At a BF content of 6 kg/m³, BFC had the strongest ability to resist sulphate erosion, and the cube compressive strength, axial compressive strength, and modulus of elasticity of BFC were the highest, with 47.8 MPa, 33.6 MPa, and 38.7 GPa, respectively. The dense calcium silicate hydrate (C-S-H) gel, generated near the BF, enhanced the connection between the cementitious and the aggregate, inhibited the development of microcracks within the concrete, and reduced the erosion channels for sulphate ions. The maximum displacement of the BFC secondary lining structure was reduced by 20.15 % compared to plain concrete (PC) after sulphate erosion. The secondary lining structures consisting of both BFC and PC were stressed the most at footing. The secondary lining structure composed of BFC had better deformation resistance and higher strength than PC.

Conjugated layered and tunnel structure enables long-lifespan and high-rate sodium-ion battery cathodes

A cathode material Na0.42Mn0.96Ti0.04O2 with conjugated layered and tunnel structures was synthesized via a convenient solid-state method. The designed conjugated structure enables superior electrochemical properties such as 93.9% capacity retention after 200 cycles at 1 C and excellent rate capability with a reversible capacity of 83.9 mAh g−1 at 20 C.

Rational Regulation of Optimal Oxygen Vacancy Concentrations on VO2 for Superior Aqueous Zinc-Ion Battery Cathodes.

VO2 with its special tunnel structure and high theoretical capacity is an ideal candidate for cathode materials for aqueous zinc-ion batteries (ZIBs). However, the slow kinetics and structural instability due to the strong electrostatic interactions between the host structure of VO2 and Zn2+ hinder its application. Defect engineering is a well-recognized strategy for improving the intrinsic ion-electron dynamics and structural stability of this material. However, the preparation of oxygen vacancies poses significant difficulties, and it is challenging to control their concentration effectively. Excessive or insufficient vacancy concentration can have a negative effect on the cathode material. Herein, we propose electrode materials with controlled oxygen vacancies prepared in situ on carbon nanofibers (CNF) by a simple, one-step hydrothermal process (Ov-VO2@CNF). This method can balance the adsorption energy and migration energy barrier easily, and we maximized the adsorption energy of Zn2+ while minimizing the adsorption energy barrier. Notably, the Ov2-VO2@CNF electrode delivered a high specific capacity (over 450 mAh g-1 at 0.1 A g-1) and excellent cycle stability (318 mAh g-1 at 5 A g-1 capacity after 2000 cycles with a capacity retention of 85%). This rational design of precisely regulated defect engineering provides a way to obtain advanced electrode materials with excellent comprehensive properties.

Fluorine-doped Na0.65MnO2 with a layer-tunnel structure for high-rate and long-cycle-life sodium-ion cathodes

Sodium-ion batteries (SIBs) exhibit comprehensive advantages in excellent cycling stability and high-rate performance. In this work, we present a novel cathode with a layered-tunnel coexisted structure with F ions, denoted as Na0.65MnO2-xFx. This material was confirmed the coexistence of layered and rod-like tunnel structures by advanced characterization methods. Due to the high specific capacity of the layered structure and the cycling stability of the rod-like tunnel structure, the Na0.65MnO2-xFx (x=0.2) cathode material exhibits outstanding comprehensive performance. At a rate of 0.1 C, the reversible discharge specific capacity is 124.6 mAh g−1, and notably, after 1000 cycles at a high rate of 10 C, the specific capacity is 55.9 mAh g−1 with a capacity retention rate of 98.2 %. This is significantly higher than the 34.1 mAh g−1 and 48.3 % capacity retention of pristine Na0.65MnO2. The introduction of F leads to an increase in the spacing between the oxide layers, the formation of strong metallic bonds and the formation of composite structures, which not only enhances the stability of the transition metal layer structure but also induces complex changes in the microstructure. This approach of ion doping and microstructure optimization provides a fresh perspective for the design and optimization of high-performance materials for SIBs.

Soil-tunnel interaction under the effect associated with the longitudinal direction

Longitudinal structural analysis of shield tunnels is studied by considering the tunnel as a Timoshenko beam based on elastic foundations under Vlasov's theory. This article presents the structural behavior of a Timoshenko-Vlasov beam jointly, using a single differential system that brings together all the equilibrium and deformation equations. Solving the presented formulation, shield tunnels can be covered under any type of action, ground pressure and support or boundary conditions. This new compacted notation facilitates the possibility of expressing the interaction between soil and structure by introducing the variability of longitudinal support conditions on the elastic springs. This differential system is resolved with the numeric procedure named Finite Transfer Method. To verify the effectiveness of the procedure followed, the structure of the subway tunnel in Shanghai has been modeled and the results obtained have been compared with those offered in the literature. The proposed model has been exemplified by introducing the variability of longitudinal elastic spring conditions representing actual soil behavior.

Optimal intensity measure for seismic performance assessment of shield tunnels in liquefiable and non-liquefiable soils

Relating the ground motion intensity measure (IM) and the structural engineering demand parameter is a crucial step in the performance-based earthquake engineering framework. This study investigates the selection of IM for development of probabilistic seismic demand model of urban shield tunnels subjected to earthquake ground motions in liquefiable and non-liquefiable soils. Nonlinear dynamic effective stress analyses are conducted to develop a database of the intensity measures and structural seismic responses exposed to ground shaking and soil liquefaction. Two advanced soil constitutive models (i.e., Pressure DependMultiYield03 and PressureIndependMultiYield for liquefiable and non-liquefiable soils, respectively) are employed to capture the nonlinear behavior. A suite of 23ground motion intensity measures is selected and assessed based on the evaluation criteria of correlation, efficiency, practicality and proficiency. Eventually, the multi-level fuzzy comprehensive evaluation method is employed to comprehensively consider the four evaluation criteria and establish the optimal ground motion IM suitable for probabilistic seismic demand analysis of shield tunnel structures. The obtained results show that the sustained maximum acceleration is the optimal IM for evaluating the structural seismic response, followed by the peak ground acceleration in both liquefiable and non-liquefiable soils. Peak pseudo velocity spectrum, displacement square integral and Housner spectral intensity are found to be not suitable for the probabilistic seismic demand analysis of shield tunnel structures.

Defects introducing and heterostructures engineering synergistically constructing active sites for achieving stable and fast ion transport in sodium-ion batteries

Bronze phase TiO2 (TiO2(B)) has attracted significant interest as potential anode materials for sodium-ion batteries (SIBs) due to its distinctive open tunnel structure, offering abundant insertion sites for Na+-ions. However, the practical application has been hindered by its poor electrical conductivity and insufficient Na+ diffusion kinetics. Herein, we propose a novel strategy that integrates defect introducing and heterostructures engineering to enhance the performance of TiO2(B) anode. Specifically, we aim to induce oxygen vacancies (OVs) into TiO2(B) through N-doping and in-situ growth on MXenes nanosheets, thereby fabricating N-doped TiO2(B)/MXenes (N-TiO-MX) heterostructures. This strategy leverages the synergistic effects of OVs and N-atoms, along with the formation of heterointerfaces, to effectively reduce the bandgap, increase the number of Na+-ion storage sites, and shorten ion diffusion distances. The robust coupling between TiO2(B) and MXenes ensures the structural integrity of N-TiO-MX heterostructures. Consequently, the N-TiO-MX exhibits a high specific capacity of 211.3 mAh g−1 at 0.1 A g−1 after 400 cycles and superior cycling stability with 163.1 mAh g−1 after 1000 cycles at 1.0 A g−1. The study provides unique insights for designing heterostructure materials to achieve high capacity and excellent fast-charging capability.

Intelligent Prediction and Application Research on Soft Rock Tunnel Deformation Based on the ICPO-LSTM Model

In tunnel construction, the prediction of the surrounding rock deformation is related to the construction safety and stability of the tunnel structure. In order to achieve an accurate prediction of the surrounding rock deformation in soft rock tunnel construction, a Long Short-Term Memory (LSTM) neural network is used to construct a prediction model of the vault settlement and the horizontal convergence of the upper conductor in soft rock tunnels. The crested porcupine optimisation (CPO) algorithm is used to realise the hyper-parameter optimisation of the LSTM model and to construct the framework of the calculation process of the CPO-LSTM model. Taking the soft rock section of the Baoshishan Tunnel as an example, the large deformation of the surrounding rock is measured and analysed in situ, and the monitoring data of arch settlement and superconducting level convergence are obtained, which are substituted into the CPO-LSTM model for calculation, and compared and analysed with traditional machine learning and optimisation algorithms. The results show that the CPO-LSTM model has an R2 of 0.9982, a MAPE of 0.8595% and an RMSE of 0.1922, which are the best among all the models. In order to further improve the optimisation capability of the CPO, some improvements were made to the CPO and an Improved Crested Porcupine Optimiser (ICPO) was proposed. The ICPO-LSTM prediction model was established, and the ZK6 + 834 section was selected as a research object for comparison and analysis with the CPO-LSTM model. The results of the error analysis show that the prediction accuracy of the improved ICPO-LSTM model has been further improved, and the prediction accuracy of the model meets the requirements of guiding construction.

Surface construction vibration impacts on underground tunnels: Approaches for using measurements and finite-element modeling to predict vibration in the frequency and time domain

Quantitative analyses of vibration impacts on underground tunnel structures were carried out on two projects. The first project was a new facility situated above an existing physics laboratory accelerator tunnel embedded in soil where the concern was vibration interference with sensitive research. Published and in-house data for construction equipment source levels were combined with measured transfer functions, between the ground surface and the tunnel, to estimate vibration transmitted to the tunnel in the frequency domain. This case study presents an approach for site-specific evaluations of construction vibration where spectral data are needed for evaluating vibration-sensitive equipment/receivers. The second project was a new facility situated above a storm relief tunnel embedded in rock where the concern was for potential vibration damage to the tunnel. A 3-D finite-element model of the rock and tunnel structure was developed to calculate the peak particle velocity and strain response of the tunnel walls in the time domain. This case study presents an approach for site-specific evaluations of construction vibration where peak velocity amplitudes and strain data are needed for evaluating structural damage potential.

Noise radiation from a partially opened and elevated tunnel-tube

Road or railway tunnels are considered in noise prediction programs generally by neglecting any emission from the tunnel structure between the openings and replacing each tunnel mouth by additional sources simulating the sound radiated from inside to outside through these openings. The sound pressure level inside the tunnel can be derived from the analog model of a room formed by a slice cut out of the extended tunnel with two perfect reflecting planes perpendicular to the tunnel axis. The paper presents a methodology for the case of an elevated tunnel tube with an upper ventilation gap running over the entire length of the tunnel to calculate the sound pressure levels in the surrounding area more approximately using engineering models like ISO 9613-2 or others and more detailed using a particle method developed to account for complete 3-dimensional propagation problems.

Tailored crystal planes of VO2 cathode power fast Zn2+ storage

Vanadium dioxide (VO2) cathode with specific tunnel structure and favorable specific capacity is critical for developing aqueous zinc-ion batteries (AZIBs) with excellent electrochemical performance. However, sluggish electrochemical kinetics hampered its development in burgeoning energy storage devices. Herein, we tailored VO2 material with different exposed crystal planes and employed as cathodes for AZIBs. The comprehensive analyses indicate the exposed (201) and (001) crystal planes are favorable for fast electrochemical kinetics, high capacitance storage, and the smallest diffusion energy barrier, which guarantee electrodes with high discharge capacity (367 mA h/g at 0.1 A/g), excellent rate capability (281 mA h/g at 4 A/g) and cycling stability over 800 cycles. Besides, Ex-situ characterizations manifest VO2 cathode with specific exposed crystal planes easily transformed to Zn3+x(OH)2V2O7·2H2O in the first discharge process, hence allowing continuous embedding of Zn2+ in this layered structure, and the ex-situ scanning electron microscopy (SEM) analysis confirms the morphology change matched well with the structural transformation. This study may enlighten and promote the role of exposed crystal plane to develop high-performance rechargeable batteries.

A Novel Hydrated Iron Vanadate Cathode Material for Advanced Aqueous Nickel-Ion Batteries.

Aqueous nickel-ion batteries (ANIBs) as an emerging energy storage device attracted much attention owing to their multielectron redox reaction and dendrite-free Ni anode, yet their development is hindered by the divalent properties of Ni2+ and the lack of suitable cathode materials. Herein, a hydrated iron vanadate (Fe2V3O10.5∙1.5H2O, FOH) with a preferred orientation along the (200) plane is innovatively proposed and used as cathode material for ANIBs. The FOH cathode exhibits a remarkable capacity of 129.3 mAh g-1 at 50mA g-1 and a super-high capacity retention of 95% at 500mA g-1 after 700 cycles. The desirable Ni2+ storage capacity of FOH can be attributed to the preferentially oriented and tunnel structures, which offer abundant reaction active planes and a broad Ni2+ diffusion path, the abundant vacancies and high specific surface area further increase ion storage sites and accelerate ion diffusion in the FOH lattice. Furthermore, the Ni2+ storage mechanism and structural evolution in the FOH cathode are explored through ex situ XRD, ex situ Raman, ex situ XPS and other ex situ characteristics. This work opens a new way for designing novel cathode materials to promote the development of ANIBs.

Analysis of Water Seepage Mechanism and Study on Mechanical Properties of Highway Tunnel Based on Fluid-Structure Coupling

Shaoguan was hit by a extremely heavy rainstorm, and the mountain water catchment of Dabaoshan Tunnel in the southern section of Beijing Hong Kong Macao Expressway in Guangdong increased sharply. Due to the rapid rise of groundwater level, water and mud gushed at ZK141+227 of Dabaoshan, and serious water seepage occurred in other areas, bringing soil into the tunnel, which seriously hindered the safe passage of the tunnel. According to the on-site investigation of water and mud gushing, it was found that there were branches sandwiched in the mud gushing out, and at the same time, it was found that there was water leakage at the foot of some walls where drainage holes were added. Based on the fluid structure coupling mechanism, the seepage mechanism of highway tunnels was deeply explored, and the mechanical properties of tunnels under seepage were analyzed through experimental data and numerical simulation. The experimental results show that under the action of seepage, the stress distribution of the tunnel lining changes, and the phenomenon of local stress concentration is obvious. When the seepage pressure reaches 3.5 MPa, cracks appear in the tunnel lining, with a total of 5 cracks. The distribution of cracks is closely related to the seepage field. The numerical simulation further reveals the interaction mechanism between the seepage field and the tunnel structure, confirming the influence of the seepage field on the stability of the tunnel lining. When the seepage pressure increases to 4.0 MPa, the displacement change rate of the tunnel lining reaches 0.3 mm/m, and the maximum lining stress is 15.7 MPa. The purpose of this study is to propose a maintenance plan for highway tunnels to improve their safety. Consider the impact of seepage on tunnel structure and adopt effective waterproofing and drainage design. Further research on the seepage mechanism and tunnel mechanical properties is recommended to provide more reliable theoretical support for engineering applications.