Three-dimensional Tunnel Research Articles

Supramolecular Crystals based Fast Single Ion Conductor for Long-Cycling Solid Zinc Batteries.

The solid polymer electrolytes (SPEs) used in Zn-ion batteries (ZIBs) have low ionic conductivity due to the sluggish dynamics of polymer segments. Thus, only short-range movement of cations is supported, leading to low ionic conductivity and Zn2+ transference (tZn 2+). Zn-based supramolecular crystals (ZMCs) have considerable potential for supporting long-distance Zn2+ transport; however, their efficiency in ZIBs has not been explored. The present study developed a ZMC consisting of succinonitrile (SN) and zinc bis (trifluoromethylsulfonyl) imide (Zn(TFSI)2), with a structural formula identified as Zn(TFSI)2SN3. The ZMC has ordered three-dimensional tunnels in the crystalline lattices for ion conduction, providing high ionic conductivities (6.02×10-4 S cm-1 at 25 °C and 3.26×10-5 S cm-1 at -35 °C) and a high tZn 2+ (0.97). We demonstrated that a Zn‖Zn symmetrical battery with ZMCs has long-term cycling stability (1200 h) and a dendrite-free Zn plating/stripping process, even at a high plating areal density of 3 mAh cm-2. The as-fabricated solid-state Zn battery exhibited excellent performance, including high discharge capacity (1.52 mAh cm-2), long-term cycling stability (83.6 % capacity retention after 70000 cycles (7 months)), wide temperature adaptability (-35 to 50 °C) and fast charging ability. The ZMC differs from SPEs in its structure for transporting Zn2+ ions, significantly improving solid-state ZIBs while maintaining safety, durability, and sustainability.

Three-dimensional tunnel face stability using a new heterogeneous dynamic filter cake

In slurry-shield tunnelling, a heterogeneous dynamic filter cake occurs due to the interaction between slurry infiltrating and tool cutting, whose influence on tunnel face stability is not fully plumbed. Thus, a numerically based-limit analysis framework is proposed to assess the tunnel face stability considering a heterogeneous dynamic filter cake. The numerical model with a heterogeneous dynamic filter cake, which has spatio-temporally variable permeability coefficients according to cutter layouts, is built for solving a transient seepage flow. Numerically obtained seepage flow results are further incorporated into the 3D rotational failure mechanism, so as to give an upper-bound estimation on the tunnel face safety factor and the slurry pressure transfer efficiency. The proposed method is validated by comparing with previous studies regarding the slurry pressure drop, slurry pressure transfer efficiency, and tunnel face safety factors. Parametric analyses are performed to examine the excess pore pressure distributions at the filter cake-soil interface, and discuss the influences of cutterhead rotation and excess slurry pressures on the tunnel face stability. The results show that the defined three-dimensional pressure transfer efficiency is between the one-dimensional and the two-dimensional solutions published previously; the tunnel face stability reduces as cutterhead rotating and finally reaches a dynamic equilibrium state.

Stability analysis of three-dimensional tunnel roofs in soil based on a modified MC criterion

Stability analysis of three-dimensional tunnel roofs in soil based on a modified MC criterion

Stability Analysis of Three-Dimensional Tunnel Face Considering Linear and Nonlinear Strength in Unsaturated Soil

The shear strength of unsaturated soils exhibits significant nonlinearity, while previous studies often simplified it with linear strength models. The objective of this paper is to investigate the distinctions in the stability of three-dimensional (3D) tunnel faces when using linear and nonlinear strength models. A new 3D rotational failure mechanism and an extended form of the Mohr–Coulomb (M-C) failure criterion were integrated into the kinematically limited analysis (KLA) framework to describe the failure characteristics of tunnel faces. Subsequently, the factor of safety (FS) of the 3D tunnel faces was calculated using the strength reduction method (SRM). In the discussion section, the impacts of nonlinear shear strength, matric suction in the unsaturated soils, and the 3D geometric parameters of the tunnel on the stability of the tunnel face were analyzed. The outcomes indicate that, in unsaturated soil conditions, diverse nonlinear strength calculation models and soil types exert disparate influences on the FS of 3D tunnel faces. The main novelty of this study lies in establishing an effective method for assessing the stability of tunnel faces in unsaturated soils.

Boosting sodium storage performance of Na0.44MnO2 through surface modification with conductive polymer PPy utilizing sonication-assisted dispersion.

The search for suitable electrode materials for sodium storage in sodium-ion batteries (SIBs) poses significant challenges. Na0.44MnO2 (NMO) has emerged as a promising candidate among various cathode materials due to its distinct three-dimensional tunnel structure, which facilitates Na+ diffusion and governs structural stress fluctuations during Na+ intercalation/deintercalation. However, NMO faces obstacles such as limited electronic conductivity, lattice distortion induced by the Jahn-Teller effect of Mn3+ during cycling, and Mn3+ disproportionation leading to material dissolution, which affects cycling durability. To overcome these problems, Na0.44MnO2/polypyrrole (NMO/PPy) composites were fabricated through surface modification of the conductive PPy using an ultrasonically assisted dispersion method. Experimental results show that NMO/PPy with a 7 wt% PPy content exhibits superior sodium storage capabilities. Specifically, at a current density of 0.5C, the initial specific discharge capacity reaches 135.2 mA h g-1, a 12.1% increase over pristine NMO, with a capacity retention of 94.5% after 100 cycles. Of particular note is a capacity retention of 82% after 500 cycles at 1C, attributed to the PPy coating, which suppresses Mn3+ side reactions, enhances the structural stability and electronic conductivity of NMO, and accelerates Na+ diffusion. These results suggest that the use of conductive polymer coatings represents a simple and effective strategy to improve the sodium storage capacity of NMO, paving the way for the further development of high-performance SIB cathodes.

Noncentrosymmetric Na6Pb3P4S16 and Centrosymmetric K2MIIP2S6 (MII = Mg and Zn) Displaying Multiple Membered-Ring Configurations and Strong Optical Anisotropy.

Three thiophosphates including noncentrosymmetric Na6Pb3P4S16 and centrosymmetric K2MIIP2S6 (MII = Mg and Zn) were successfully synthesized in vacuum-sealed silica tubes. Note that interesting multiple six membered-rings (6-MRs) including 6-NaS6-MRs and 6-KSn-MRs (n = 6 and 7) formed by A+-centered polyhedra were discovered in the structures of title thiophosphates and these MR-composed three-dimensional (3D) tunnels show great possibility to facilitate the filling of various structural blocks (such as zero-dimensional (0D) Pb3S10 trimers or one-dimensional (1D) (MIISn)n chains). Na6Pb3P4S16 exhibits the strongest nonlinear optical (NLO) response (5.4 × AgGaS2) with phase-matching (PM) behavior among the known Pb-based PM NLO sulfides, which is much larger than that of Pb3P2S8 (3.5 × AgGaS2); it was verified that such large second harmonic generation (SHG) response in Na6Pb3P4S16 can be attributed to the huge contribution of stereochemically active PbS4 units based on the SHG-density and dipole-moment calculations. Moreover, title thiophosphates show large birefringences (Δn = 0.102-0.21), which indicates that incorporation of [P2S6] dimers or polarized PbS4 units into structures provides positive benefits for the onset of strong optical anisotropy.

Calcium sulfate-Cu2+ delivery system improves 3D-Printed calcium silicate artificial bone to repair large bone defects

There are still limitations in artificial bone materials used in clinical practice, such as difficulty in repairing large bone defects, the mismatch between the degradation rate and tissue growth, difficulty in vascularization, an inability to address bone defects of various shapes, and risk of infection. To solve these problems, our group designed stereolithography (SLA) 3D-printed calcium silicate artificial bone improved by a calcium sulfate-Cu2+ delivery system. SLA technology endows the scaffold with a three-dimensional tunnel structure to induce cell migration to the center of the bone defect. The calcium sulfate-Cu2+ delivery system was introduced to enhance the osteogenic activity of calcium silicate. Rapid degradation of calcium sulfate (CS) induces early osteogenesis in the three-dimensional tunnel structure. Calcium silicate (CSi) which degrades slowly provides mechanical support and promotes bone formation in bone defect sites for a long time. The gradient degradation of these two components is perfectly matched to the rate of repair in large bone defects. On the other hand, the calcium sulfate delivery system can regularly release Cu2+ in the temporal and spatial dimensions, exerting a long-lasting antimicrobial effect and promoting vascular growth. This powerful 3D-printed calcium silicate artificial bone which has rich osteogenic activity is a promising material for treating large bone defects and has excellent potential for clinical application.

KBi(SeO4)(IO3)Cl: A mixed-anion oxychloride with three types of building units in one structure

A novel mixed-anion oxychloride, KBi(SeO4)(IO3)Cl, has been hydrothermally synthesized and structurally characterized. The compound crystallizes in the monoclinic space group of P21/c with cell parameters of a = 7.8802(2) Å; b = 10.8088(2) Å, c = 10.1364(2) Å, β = 112.849(1)°, V = 795.62(3) Å3, and Z = 4. KBi(SeO4)(IO3)Cl exhibits a three-dimensional tunnel framework that is composed of three types of atomic groups, i.e., tetrahedral SeO4, trigonal pyramidal IO3, and polyhedral BiO6Cl. Both IO3 pyramid and BiO6Cl polyhedron are in strongly acentric coordination due to the influence of I5+ and Bi3+ lone electron pairs. The measurement of UV–vis–NIR spectra for powder KBi(SeO4)(IO3)Cl indicates that the material is a wide band gap semiconductor with Eg = 3.9 eV. Theoretical analysis shows that the electron transition from Bi 6p to O 2p states in the BiO6Cl unit dominates the optical absorption edge. Thermal stability and IR spectrum were also analyzed for the material.

Construction Method for a Three-Dimensional Tunnel General Monomer Model Based on Parallel Pathfinding

Existing approaches for the 3D modeling of tunnels suffer from several problems, such as highly difficult data acquisition, redundancy of model data, large computational burden, and the inability of the resulting models to be monolithic. Therefore, solutions to the tunnel network modeling problem for complex structures need to be proposed and elaborated in detail. In this paper, a construction method for a three-dimensional tunnel general monomer model based on parallel pathfinding is proposed. Widely used tunnel CAD drawings are analyzed and read, a disordered arc ensemble intersection trend decision method is developed, and an automatic path extraction solution algorithm for unidirectional modeling of tunnel centerlines is constructed. By constructing and splicing the surface elements of the 3D model, a monomeric 3D tunnel model representing the complex network structure is finally obtained. Moreover, the modeling of shafts is realized based on the monomer model, allowing for the three-dimensional topological relationships between different sub-levels of the tunnel and the ground to be established. The automatic modeling method proposed in this paper is applied to the digital twin platform of a filling project in a mining area in Gansu province, China. The experimental results demonstrate that the 3D tunnel models constructed in this way have a smaller data volume, higher modeling accuracy, and more stable growth of modeling speed.

Pseudo-dynamic analysis of a 3D tunnel face in inclined weak strata

A new discretization technique is proposed for a three-dimensional (3D) tunnel face in weak strata with a random position in space. This method limits the angle, height, and thickness of the strata on the tunnel face. The original whole piece of soil is separated by a series of parallel planes, and two parallel planes are used as a stratum. Each radial discrete plane is separated when it passes through the strata, and the change in the soil properties of discrete points on the truncated plane is considered separately inside the strata. Considering the spatial and temporal characteristics of seismic waves, a pseudo-dynamic analysis of the tunnel face is carried out. The tunnel face active damage types under earthquake conditions are quantitatively analyzed, and the corresponding support pressure design diagrams are given for the case without weak strata. For the case containing weak strata, the presence of weak strata can have adverse effects on the face. The failure mechanism of the weak strata is given by the discretization method. For different friction angles, the presence of the weak strata changes the friction angles of the soils. For the thickness, location and angle of the weak strata, the variation in the support pressure is given in this paper. To more intuitively depict the change in the failure mechanism in the presence of weak strata, the change in the failure mechanism under different thicknesses and weaknesses of weak strata is plotted.

A Three-Dimensional Elastoplastic Constitutive Model for Geomaterials

The Mohr-Coulomb (M-C) failure criterion has been a popular choice for geotechnical analysis because of its simplicity and ease of use. The fact that the M-C criterion disregards the intermediate principal stress’s impact is a significant drawback. As a result, the M-C criterion is only applied to materials under biaxial stress. This paper presents a three-dimensional version of the M-C criterion. The proposed criterion, called the Generalized Mohr-Coulomb (GMC) criterion, considers the intermediate principal stress’s effect, in addition to inheriting the original M-C criterion’s benefits. We obtained the conditions that the strength parameters must satisfy when the GMC criterion fulfills the π plane’s convexity. The GMC criterion can better describe geotechnical materials’ strengths under general stress conditions. Based on an implicit algorithm, the user material subroutine (UMAT) of the three-dimensional GMC model was developed in ABAQUS using the Fortran programming language. The established elastoplastic model’s validity and the program’s accuracy were examined using numerical simulation. Finally, a numerical simulation of a three-dimensional tunnel excavation under various working conditions was performed. The calculation results from the GMC model are precise and have some engineering-related practical significance.

Elastic waveform inversion in the frequency domain for an application in mechanized tunneling

The excavation process in mechanized tunneling can be improved by reconnaissance of the geology ahead. A nondestructive exploration can be achieved in means of seismic imaging. A full waveform inversion approach, which works in the frequency domain, is investigated for the application in tunneling. The approach tries to minimize the difference of seismic records from field observations and from a discretized ground model by changing the ground properties. The final ground model might be a representation of the geology. The used elastic wave modeling approach is described as well as the application of convolutional perfectly matched layers. The proposed inversion scheme uses the discrete adjoint gradient method, a multi-scale approach as well as the L-BFGS method. Numerical parameters are identified as well as a validation of the forward wave modeling approach is performed in advance to the inversion of every example. Two-dimensional blind tests with two different ground scenarios and with three different source and receiver station configurations are performed and analyzed, where only the seismic records, the source functions and the ambient ground properties are provided. Finally, an inversion for a three-dimensional tunnel model is performed and analyzed for three different source and receiver station configurations.

Stable Rb-B compounds under high pressure

As a frontier issue of physics and material, the structures and related properties of borides have been extensively investigated in fundamental science. The search for pressure-induced stable compounds has become a feasible approach to acquire borides that are inaccessible at atmospheric pressure. Combined with state-of-the-art swarm intelligence structure prediction and first-principles calculations, we systematically explored the Rb-B system and uncovered a series of unprecedented RbB, ${\mathrm{Rb}}_{2}{\mathrm{B}}_{3}$, ${\mathrm{RbB}}_{3}$, ${\mathrm{RbB}}_{6}$, ${\mathrm{RbB}}_{8}$, and ${\mathrm{RbB}}_{10}$ under high pressure. It is found that the catenation of boron evolves from linear chain to layered sheets, clusterlike units, and further to three-dimensional tunnel structures with increasing boron content. Among them, ${\mathrm{RbB}}_{6}$ and ${\mathrm{RbB}}_{8}$ are expected phonon-mediated superconductors with ${T}_{c}$ of \ensuremath{\sim}12 K and superhard material with a hardness of \ensuremath{\sim}37 GPa at ambient pressure, respectively. Additionally, ${\mathrm{RbB}}_{8}$ is a suitable precursor for obtaining the superconducting $o\text{\ensuremath{-}}{\mathrm{B}}_{16}$ boron allotrope by removing Rb due to its better stability than isomorphic ${\mathrm{SrB}}_{8}$. The current results provide insights into the design of unforeseen borides and illustrate intriguing B-B bonding features originating from Rb \ensuremath{\rightarrow} B charge transfer under pressures.

3C-3D tunnel seismic reverse time migration imaging: A case study of Pearl River Delta Water Resources Allocation Project

In recent years, tunnel boring machines (TBMs) have been widely used because of their fast construction speed and economical benefits, and the need to obtain geological information ahead of the tunnel to ensure the TBM tunnel construction safety has also arisen. Faced with the complex geological environment, seismic forward-prospecting is the primary method for predicting the unfavorable geological structure in front of the tunnel face. As a crucial step in seismic forward-prospecting method, migration can image geological characteristics and help learn the distribution of unfavorable geology. To achieve all-round imaging of unfavorable geology, we suggested a three-component (3C) three-dimensional (3D) tunnel seismic reverse time migration imaging method. The acoustic wave equation is employed for the forward and backward wavefield extrapolation after the P/S-wave separation to eliminate the imaging artifacts from severe converted waves in tunnels. GPU parallelization is used to accelerate the calculation to further adapt to the rapid excavation of TBMs. The proposed method is validated in two typical numerical models, especially for 3C seismic data that provides all-round geological information to achieve enhanced imaging energy and artifact reduction, which demonstrates the significance of 3C seismic data to migration imaging. This case study was conducted in the Pearl River Delta Water Resources Allocation Project in Guangdong Province, China. The reliability of 3C3D tunnel seismic reverse time migration imaging in field tunnel engineering was investigated. Two consecutive detections were performed, and then the spatial positions of faults and fractures in front of the tunnel face were accurately judged by the combination of the two imaging results. Based on the detection results, the excavation rate was slowed down and the tunnel lining support was increased. The TBM then successfully passed through the risk areas. This case study can serve as a reference for other tunnels with similar concerns regarding the necessity of 3C seismic data and consecutive detections.

Investigation on Cable Temperature in Wet Tunnel Considering Coupled Heat and Moisture Transfer

Many elder tunnels often lack waterproofing facilities, and water can easily accumulate in tunnel bottom or even on cable surface. Using the finite element method (FEM), the three-dimensional tunnel cable model, which couples the fluid field, the heat transfer and the moisture transport, is developed in our study. The coupling effects especially the phase change behavior are comprehensively considered. It indicates that a high humid environment would benefit the heat dissipation. Depending on the initial vapor content, water distribution, and cable arrangement, the maximum cable temperature may drop to some extent ranging from 2 °C to 10 °C. The presence of water changes the thermal properties of air, including the thermal conductivity and heat capacity. The latent heat caused by evaporation accounts for a greater portion compared to conduction. The presence of water changes the vapor concentration distribution of tunnel. It is mainly located near the cable surface within a distance of 0.02 m, and it decreases drastically away from the cable. In addition to common radial heat transfer, both the longitudinal and circumferential heat flux exists arising from the movement of fluid flow and water evaporation.

Application of BIM in Tunnel Design with Compaction Pile Reinforced Foundation Carrying Carbon Assessment Based on Advanced Dynamo Visual Programming: A Case Study in China

Carbon emission assessment in civil engineering has gained worldwide attention due to the negative effects of greenhouse gases on the environment. Significant amounts of building materials and electric power are consumed during the construction of tunnels, causing the release of greenhouse gases into the atmosphere. In addition, building information modeling (BIM) can be utilized to realize the computerized design of tunnels, and improve construction efficiency. However, the traditional BIM software (Autodesk Revit) lacks tunnel components and is unable to directly create a three-dimensional tunnel axis. This paper adopted BIM to build a three-dimensional model of the tunnel components for tunnel and carried out batch parameterization and component lofting based on Dynamo visual programming. The BIM of the tunnel guided the construction procedures and improved the construction efficiency. Based on the emission coefficient method, we calculated the carbon emissions from each component and loaded them into the BIM during the parameterization process. After the tunnel modeling design was completed, a bill of quantities was obtained. Then, the carbon emissions from the whole tunnel construction were calculated according to the bill. Thus, the combination of BIM technology and tunnel engineering was realized; this has practical significance for reductions in emissions, and cleaner construction in relation to tunnel engineering.

High crystallinity potassium nickel hexacyanoferrate nanoparticles synthesized by improved precipitation way as cathodes for potassium-ion batteries

Due to the unique three-dimensional tunnel structure, Prussian blue analogues can reversibly de/intercalate K+ in crystal lattice and show original electrochemical properties. However, crystal water and vacancy inevitably appear in the framework controlled by synthesis process, limiting severely the potassium storage. Herein, high crystallinity K1.86Ni[Fe(CN)6]0.87·□0.13·1.88H2O was synthesized through electrostatic assisted coprecipitation technology, which effectively increased the initial potassium content. Moreover, the microstructure is affected under the action of static electricity, resulting in a nano-structure and large specific surface area (102.5 m2 g−1). Compared with the sample without electrostatic field, its electrochemical performances can be significantly improved with a high initial coulombic efficiency of 85.5%, capacity retention of 90.3% after 503 cycles at 1C and rate capability of 49 mAh g−1 at 10C. The new method opens up a way for the performance improvement of other Prussian blue-based cathodes.

Spectroscopic Monitoring of the Electrode Process of MnO2@rGO Nanospheres and Its Application in High-Performance Flexible Micro-Supercapacitors.

Structural instability is a major obstacle to realizing the high performance of a MnO2-based pseudocapacitor material. Understanding its structure transformation in the process of electrochemical reaction, therefore, plays an important role in the efficient enhancement of rate capacity and stability. Herein, a stable MnO2@rGO core-shell nanosphere is first synthesized by a liquid-liquid interface deposition further combined with the electrostatic self-assembly method. The structural transformation process of the MnO2@rGO electrode is monitored by ex situ Raman and X-ray diffraction spectroscopy during the charging-discharging process. It is found in the first discharging process that layered-MnO2 transforms into the spinel-Mn3O4 phase with K+ ion intercalation. From the second charging, the spinel-Mn3O4 phase is gradually adjusted to a more stable λ-MnO2 with a three-dimensional tunnel structure, finally realizing the reversible intercalation/deintercalation of K+ ions in the λ-MnO2 tunnel structure during subsequent cycling, which can be attributed to the presence of oxygen vacancies formed by the lengthening of the Mn-O bond and losing oxygen in the MnO6 octahedral unit with K+ ion intercalation/deintercalation. Meanwhile, the MnO2@rGO electrode demonstrates a high specific capacitance of 378 F g-1 at 1 A g-1 and excellent cycling stability with a capacitance retention of up to 89.5% after 10 000 cycles at 10 A g-1. Furthermore, the assembled symmetric micro-supercapacitor delivers a high areal energy density of 1.01 μWh cm-2, superior cycling stability with no significant capacity decay after 8700 cycles, and a capacity retention rate of almost 100% after 2000 bending cycles, showing great mechanical flexibility and practicability.

Second-Harmonic Generation-Positive Na2Ga2SiS6with a Broad Band Gap and a High Laser Damage Threshold

The development of high-power solid-state lasers is in urgent need of new infrared nonlinear optical (IR NLO) materials with a wide band gap and a high laser-induced damage threshold. A new infrared nonlinear optical material Na2Ga2SiS6 has been synthesized for the first time, crystallizing in the Fdd2 (no. 43) noncentrosymmetric space group. Its three-dimensional tunnel framework consists of two typical NLO active motifs [GaS4] and [SiS4], with Na+ cations located inside the tunnels. Na2Ga2SiS6 exhibits comprehensive optical properties, namely, a wide transmission range, a high laser-induced damage threshold (10 × AgGaS2), a type-I phase-matching second-harmonic generation response (0.2 × AgGaS2), and especially a wide band gap (3.93 eV), which is the largest in the A2MIII2MIVQ6 (A = alkali metals; MIII = IIIA elements; MIV = IVA elements; Q = S and Se) family. Therefore, Na2Ga2SiS6 does not produce two-photon absorption under a 1064 nm laser pump and could be used in high-energy laser systems, which makes Na2Ga2SiS6 a promising candidate for high-energy IR NLO applications.

Three-dimensional tunnel face stability considering slurry pressure transfer mechanisms

In slurry-shield tunneling, the bentonite slurry tends to infiltrate into the soil skeleton ahead of the tunnel face, causing a forward seepage flow associated with excess pore pressures in the ground. Both the slurry infiltration and the forward seepage flow significantly impact the tunnel face stability. In the present paper, a kinematic approach of limit analysis with the classical three-dimensional discretized rotational failure mechanism is employed to assess the face stability of a slurry-shield-driven tunnel. Three situations of slurry infiltrations that influence the face pressure transfer mechanisms were considered: a full filter cake, a penetration zone, and pure groundwater flow without a filter cake or a penetration zone. The pore pressure distributions surrounding the tunnel face were firstly obtained using numerical calculations. Afterward, the incorporation of numerically obtained pore pressure distributions into the work rate calculations allows considering a three-dimensional forward seepage flow ahead of the tunnel face, which provides a rigorous upper-bound estimation to the tunnel face safety factor determined by the strength reduction technique. The proposed method is validated by comparing the calculated results with those provided by previously published literature. The effects of excess slurry pressures, hydraulic conditions, pressure drop coefficients, and soil shear strength were investigated. Several design charts are given for practical application.