Tunneling Properties Research Articles

Numerical and Statistical Evaluation of the Performance of Carbon Fiber-Reinforced Polymers as Tunnel Lining Reinforcement during Subway Operation

Ground vibrations during train operations have become a serious problem in recent years. Local residents often feel disturbed by the vibrations emanating from the railroad line. This inconvenience is particularly pronounced in loose areas traversed by subways. However, improving the mechanical properties of tunnels has been the subject of several studies. Among these works, the widely discussed fiber-reinforced polymer (FRP) is considered as a material that can be incorporated into the tunnel structure to increase stiffness, durability, and corrosion resistance. However, the function of FRP in the interaction between the soil and the tunnel during operation has scarcely been studied. In this study, the effectiveness of carbon fiber-reinforced polymers (CFRP) as reinforcement of tunnel lining on ground vibration is investigated. For this purpose, a nonlinear 3D finite element model was developed based on a subway section in Shanghai to simulate the dynamic behavior of the system. The moving subway load was modeled as a transient dynamic load via a DLOAD subroutine, in which the rail irregularities are taken into account. The numerical model was efficiently validated by field tests. Then, the efficiency of using CFRP as concrete reinforcement of the tunnel lining during the subway operation was investigated. In addition, a statistical analysis of the ground dynamic response depending on the CFRP bars properties is presented, evaluated, and discussed.

Effect of straight bolt corrosion on mechanical properties of shield tunnel under DC stray current

The strength of straight bolt is an important index affected the mechanical properties of shield tunnel, at present most studies only focus on the effect of bolt corrosion on local structure performance under DC stray current, but the performance change of local structure cannot reflect the stiffness degradation of the whole ring tunnel structure. The purpose of the research is to study the influence mechanism of bolt corrosion on mechanical properties of shield tunnel under DC stray current. Combined with numerical and experimental analysis methods, the coupling calculation of electric, chemical and mechanical fields is realized based on the theory of electrochemical and structural mechanic, the deformation and internal force of shield tunnel contained corroded bolt are also presented. The major conclusions include: the effect of straight bolt corrosion on the deformation and internal force of shield tunnel understraightjointassembling is greater than that understaggered joint assembly. When the number of DC stray current input point is equal, the effect of bolt corrosion on tunnel deformation and internal force under current bilateral input mode is greater than unilateral input mode and hypotenuse input mode.

Research on Experimental and Numerical Methods for Mechanical Properties of Lightweight Hollow Precast Utility Tunnels

In this paper, the mechanical properties of hollow precast utility tunnels are studied by experimental and numerical methods. Through full-scale experiments, the failure modes of ordinary and hollow utility tunnels are studied, and the failure stages of the structures are classified based on the bearing capacity and damage to the structures. The nonlinear finite element model is used to simulate the behavior of the structure, and the optimal design of the structure under load type and the hollow ratio are discussed based on the finite element method. The theoretical calculation method of the bearing capacity for hollow structures in each stage is proposed, and its application scope is discussed. The finite element analysis can effectively predict the mechanical properties of the structure, and the failure of the utility tunnel structure is dependent on the shear bearing capacity. Although hollow design advances the structural damage under point load, the hollow structure has significant advantages under uniform loads or reasonable hollow ratios. It is reasonable to calculate the cracking load considering moment distribution at section centroid and the failure load considering the combined action of flexural and shear stress, but the hollow ratio should be less than 16%. Under reasonable hollow ratio or load conditions, the hollow design has little effect on the bearing capacity of the structure and can reduce the weight, which has practical value for architecture and construction.

Spin-selective tunneling from nanowires of the candidate topological Kondo insulator SmB6.

Incorporating relativistic physics into quantum tunneling can lead to exotic behavior such as perfect transmission through Klein tunneling. Here, we probed the tunneling properties of spin-momentum-locked relativistic fermions by designing and implementing a tunneling geometry that uses nanowires of the topological Kondo insulator candidate samarium hexaboride. The nanowires are attached to the end of scanning tunneling microscope tips and used to image the bicollinear stripe spin order in the antiferromagnet Fe1.03Te with a Neel temperature of about 50 kelvin. The antiferromagnetic stripes become invisible above 10 kelvin concomitant with the suppression of the topological surface states in the tip. We further demonstrate that the direction of spin polarization is tied to the tunneling direction. Our technique establishes samarium hexaboride nanowires as ideal conduits for spin-polarized currents.

New disordered anyon phase of doped graphene zigzag nanoribbon

We investigate interacting disordered zigzag nanoribbons at low doping, using the Hubbard model to treat electron interactions within the density matrix renormalization group and Hartree-Fock method. Extra electrons that are inserted into an interacting disordered zigzag nanoribbon divide into anyons. Furthermore, the fractional charges form a new disordered anyon phase with a highly distorted edge spin density wave, containing numerous localized magnetic moments residing on the zigzag edges, thereby displaying spin-charge separation and a strong non-local correlation between the opposite zigzag edges. We make the following new predictions, which can be experimentally tested: (1) In the low doping case and weak disorder regime, the soft gap in the tunneling density of states is replaced by a sharp peak at the midgap energy with two accompanying peaks. The e^-/2 fractional charges that reside on the boundary of the zigzag edges are responsible for these peaks. (2) We find that the midgap peak disappears as the doping concentration increases. The presence of e^-/2 fractional charges will be strongly supported by the detection of these peaks. Doped zigzag ribbons may also exhibit unusual transport, magnetic, and inter-edge tunneling properties.

Study on the Influence of Cracks on the Mechanical Performance of Tunnel Lining Structure Based on Fracture Mechanics Theory

The problem of tunnel lining cracking is becoming more and more common. The existence of cracks changes the stress state of lining structure and has an adverse impact on the safety of lining structure. In this paper, the mechanical properties of tunnel cracked lining structure are studied. Based on the theories of structural mechanics and fracture mechanics, the performance indexes of cracks in the arch waist of tunnel secondary lining are studied with the reference of stress intensity factor. The numerical simulation calculation is carried out. Finally, the XFEM extended finite element method is used, the crack damage of secondary lining under different crack depths is demonstrated and analyzed, and the theoretical value is compared with the numerical value. The results show that, for the cracked model (the crack depth is 12 cm), the stress and displacement at the arch waist increase greatly compared with the uncracked model and are the most significant with the increase of crack depth. In the initial stage of crack development, the growth of stress and displacement of the structure is not obvious, and the small change of crack depth in the later stage can also cause great growth of stress and displacement. Compared with the uncracked model, when the crack depth is 3 cm, the maximum vertical stress increases by 4.3 times and the maximum settlement increases by 1.3 times. When the crack depth is 18 cm, it increases by 21.2 times and 2.94 times, respectively. The research results can provide a theoretical basis for the prevention and treatment of cracks in the arch waist of tunnel secondary lining during tunnel operation.

Temperature dependence of tunnel magnetoresistance in serial magnetic tunnel junctions

Magnetic tunnel junctions have been widely used in various applications, such as magnetic sensors and magnetic random-access memories. In the practical application of MTJs, they are usually used in series toward high sensitivity and high stability, especially for sensor applications. In this paper, serial MTJs devices on 8 in. wafers were fabricated. The temperature dependence of the tunnel magnetoresistance ratio, resistances in parallel and antiparallel configurations, and dynamic conductance were systematically investigated. The results of serial MTJs devices are consistent with a single MTJ device. This research suggests that serial MTJs can be directly used to investigate the magnetic tunneling properties of MTJ stacks.

Transosseous tunnels versus suture anchors for the repair of acute quadriceps and patellar tendon ruptures: A systematic review and meta-analysis of biomechanical studies

BackgroundMultiple techniques have been developed for the repair of acute quadriceps and patellar tendon ruptures with the goal of optimizing clinical outcomes while minimizing complications and costs. The purpose of this study was to evaluate the biomechanical properties of transosseous tunnels and suture anchors for the repair of quadriceps and patellar tendon ruptures. MethodsA systematic review of the PubMed and Embase databases was performed based on the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines using specific search terms and eligibility criteria. Meta-analysis was performed by fixed-effects models for studies of low heterogeneity (I2 <25%) and random-effects models for studies of moderate to high heterogeneity (I2 ≥25%). ResultsA total of 392 studies were identified from the initial literature search with 7 studies meeting the eligibility criteria for quadriceps tendon repair and 8 studies meeting the eligibility criteria for patellar tendon repair. Based on the random-effects model for total gap formation and load to failure for quadriceps tendon repair, the mean difference was 8.88 mm (95% CI, −8.31 mm to 26.06 mm; p = 0.31) in favor of a larger gap with transosseous tunnels and −117.25N (95%CI, −242.73N to 8.23N; p = 0.07) in favor of a larger load to failure with suture anchors. A similar analysis for patellar tendon repair demonstrated a mean difference of 2.86 mm (95% CI, 1.08 mm to 4.64 mm; p = 0.002) in favor of a larger gap with transosseous tunnels and −56.34N (95% CI, −226.75 to 114.07N; p = 0.52) in favor of a larger load to failure with suture anchor repair. ConclusionsTransosseous tunnels are biomechanically similar to suture anchors for quadriceps tendon repair. Patellar tendon repair may benefit from reduced gap formation after cycling with suture anchor repair, but the load to failure for both techniques is biomechanically similar. Additional studies are necessary to evaluate these and alternative repair techniques. Level of evidenceSystematic review and meta-analysis of biomechanical studies, Level V.

Rotational Spectroscopy of 2-Furoic Acid and Its Dimer: Conformational Distribution and Double Proton Tunneling.

Structural and tunneling properties of the 2-furoic acid (FA) monomer and dimer were investigated using rotational spectroscopy and DFT calculations. CREST, a conformational ensemble space exploration tool, was used to identify all possible low-energy conformations of the FA monomer and dimer, followed by the DFT geometry optimization and harmonic frequency calculations. Broadband rotational spectra in the 2-6 and 8-12 GHz regions were recorded in a supersonic jet expansion. The monomeric FA was found to exist dominantly as three different conformers: I, II, and III in a jet, with I and II taking on the cis-COOH configuration while III having the trans-COOH configuration. For the FA dimer, only the I-II conformer was observed experimentally, whereas the symmetric I-I and II-II conformers were not observed because of their zero dipole moments. The analysis of the splittings in the rotational transitions of I-II allowed one to extract the tunneling splitting to be 1056.0(12) MHz. The barrier height was determined to be ∼442 cm-1 using the scaled potential energy scans at several different levels of theory.

Comparison of interfaces, band alignments, and tunneling currents between crystalline and amorphous silica in Si/SiO2/Si structures

Recently, to improve the performance of an integrated metal-oxide-semiconductor (MOS) device, an attempt has been made in the industry to replace the amorphous oxide with a crystalline oxide. However, various characteristics caused by the difference between amorphous and crystalline oxide in the MOS structure have not been systematically investigated. Therefore, we demonstrate the difference in atomic interface structures, electronic structures, and tunneling properties concerning varied oxide phases in a representative system, Si/SiO2/Si structures, with sub-3 nm-thick silica from first-principles. We investigate two oxide phases of amorphous (a-) and crystalline (c-) SiO2 with and without H passivation at the interface. Si/a-SiO2 exhibits a smooth interface layer, whereas Si/c-SiO2 exhibits an abrupt interface layer, resulting in the thicker interface layer of Si/a-SiO2 than Si/c-SiO2. Thus for a given total silica thickness, the adequate tunneling-blocking thickness, where all the Si atoms form four Si–O bonds, is thinner in a-SiO2 than c-SiO2, originating more tunneling current through a-SiO2 than c-SiO2. However, the effects of dangling bonds at Si/c-SiO2 rather than Si/a-SiO2 on tunneling currents are crucial, particularly in valence bands. Furthermore, when the dangling bonds are excluded by H atoms at Si/c-SiO2, the tunneling current dramatically reduces, whereas the H-passivation effect on the tunneling blocking at Si/a-SiO2 is insignificant. Our study contributes systematic knowledge regarding oxide phases and interfaces to promote for high performance of MOS devices.

Study on mechanical characteristics of support system for Shallow-buried Single-Arch subway station in rock stratum

During the construction of shallow-buried single-arch subway station, because of unstable surrounding rock and lack of design experience, failure and hazard phenomena, such as large deformation, collapse and instability of soils/rocks often occur, substantially affecting the safety of tunnel structure and construction. In the case of the Xinggongjie Station subway tunnel, Dalian, Liaoning Province, Northeast China, mechanical and deformation characteristics of support system are analyzed by numerical simulations and in-situ monitoring data. Additionally, comparative analyses are conducted for internal force of arch support in different surrounding rock pressure and in-situ monitoring result. It is concluded that the single-arch subway station usually cannot form a pressure arch characterized by shallow-buried tunnel properties; the double initial support of stacked loaded arch bear full load together in construction process, and the outer initial support bear the main load; the up-step excavation of middle pilot and dismantling temporary support are key processes in the construction control. It is found that the structure will stabilize upon the completion of the stacked loaded arch. The stacked loaded arch structure can control the stratum deformation to an acceptable range; meanwhile, it has certain safety margin and stratum adaptability. The study method and conclusions can provide references for support in-site construction and similar projects and can enrich and improve design method of the large-span single-arch station.

Josephson junctions based on amorphous MoGe: prospects for use in superconducting electronics

We have fabricated and characterized all-MoGe Josephson junctions with a very thin Al/AlO x /(Al) barrier, where the amorphous MoGe films exhibit superconducting transition temperatures up to 7 K. Due to the uniformity of the surface morphology of the MoGe films, the junctions demonstrate high uniformity of their tunneling properties. The experimental data on the temperature dependence of the subgap current agree well with theoretical calculations. The results obtained imply that Josephson tunnel junctions based on amorphous superconductors are promising candidates for use in superconducting electronics, especially in applications requiring multiple stacked junctions or the creation of a nonequilibrium quasiparticle distribution.

Geometric differences in the ribosome exit tunnel impact the folding and escape of nascent protein chains

The ribosome exit tunnel is a sub-compartment that contains the nascent polypeptide chain, and as such, is involved in the regulation of translation and other essential functions such as protein folding. Analyzing and comparing the geometry of the tunnel from high resolution structures reveal key differences between eukaryotes and prokaryotes: eukaryotic tunnels are overall shorter and narrower, with the presence of a second constriction site that is absent in prokaryotes. To understand the potential implications of these differences on translation dynamics, we studied how the geometric properties of the exit tunnel impact the folding and escape process of the nascent protein.

Operational Theories in Phase Space: Toy Model for the Harmonic Oscillator.

We show how to construct general probabilistic theories that contain an energy observable dependent on position and momentum. The construction is in accordance with classical and quantum theory and allows for physical predictions, such as the probability distribution for position, momentum, and energy. We demonstrate the construction by formulating a toy model for the harmonic oscillator that is neither classical nor quantum. The model features a discrete energy spectrum, a ground state with sharp position and momentum, an eigenstate with a nonpositive Wigner function as well as a state that has tunneling properties. The toy model demonstrates that operational theories can be a viable alternative approach for formulating physical theories.

In-plane InGaAs/Ga(As)Sb nanowire based tunnel junctions grown by selective area molecular beam epitaxy

In-plane InGaAs/Ga(As)Sb heterojunction tunnel diodes are fabricated by selective area molecular beam epitaxy with two different architectures: either radial InGaAs core/Ga(As)Sb shell nanowires or axial InGaAs/GaSb heterojunctions. In the former case, we unveil the impact of strain relaxation and alloy composition fluctuations at the nanoscale on the tunneling properties of the diodes, whereas in the latter case we demonstrate that template assisted molecular beam epitaxy can be used to achieve a very precise control of tunnel diodes dimensions at the nanoscale with a scalable process. In both cases, negative differential resistances with large peak current densities are achieved.

Mechanical Behavior of Loess Tunnels Caused by Surface Water Joints Infiltration

Many researchers have conducted a vast amount of research on water sensitivity and joint seepage in loess tunnels. However, studies on the mechanical effects of shallow buried loess tunnels under the influence of joint dominant seepage are still insufficient. In this study, we simulate the seepage range of loess tunnels with joints, and we use this seepage range to numerically simulate the mechanical properties of shallow buried loess tunnels. Studies have shown that the permeability coefficient and the number of joints are the key factors that affect the amount of surface water infiltration. An increase in the permeability coefficient on the order of 5 × 10−3 m/s will cause the surface water to pour into the ground and rapidly form a saturated soak zone on the liner, while an increase in the number of joints will increase the width and formation rate of the saturated zone. The results of the tunnel mechanics simulation show that the surface settlement and the surrounding rock displacement increase with the increase of the wetted area of the vault; the effect of arch footing water immersion on the surface settlement and the surrounding rock displacement is most significant for the same wetted area width. Compared with the three‐stage method, the center cross diaphragm (CRD) method of excavation can better control the surface and the surrounding rock settlement under waterlogged conditions. In particular, the lining settlement on the waterlogged side can be effectively controlled, and the overall settlement of the tunnel is more uniform.

Particle escape problem in semi-open system

&lt;sec&gt;We investigated the tunneling properties of a particle in a semi-open system. Starting initially from the eigenstate of the particle in the one-dimensional infinite well, we quench the infinitely high barrier on the right into a series of &lt;inline-formula&gt;&lt;tex-math id="M2"&gt;\begin{document}$\delta$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="16-20220450_M2.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="16-20220450_M2.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; barriers to observe the survival probability which is defined as the fidelity to the initial state. This constitutes a semi-Dirac comb model consisting of an infinitely high wall and multiple equally spaced &lt;inline-formula&gt;&lt;tex-math id="M3"&gt;\begin{document}$\delta$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="16-20220450_M3.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="16-20220450_M3.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;-potential barriers. We first solve the exact analytical solution of this model and obtain the closed analytic form of the eigen function expressed by a recursive relation. For a single barrier, multiple potential barriers, the disordered potential barriers, the closed-form expression of the survival probability i.e., the initial state fidelity, is given for any evolution time and it is used to reveal the mechanism of the particle escape process. The dependence of survival probability on the strength of barrier, number of barriers, and disorder strength is calculated numerically based on fast Fourier transform method. The relevant parameters are used to control and suppress the particle escape problem. We found that for a single &lt;inline-formula&gt;&lt;tex-math id="M4"&gt;\begin{document}$\delta$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="16-20220450_M4.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="16-20220450_M4.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;-potential barrier, the survival probability of the particle follows different trends in different decay time ranges. The particle in the ground state or excited states decays exponentially in a short time. After some time, the decay of the excited state will proceed with the same decay constant as that of the ground state. Finally, the survival probability follows a long-time inverse power law. The curve changes abruptly at different decay time intervals and is accompanied by significant oscillations. These oscillations in the transition region are caused by the interference of the exponential rate and the inverse power-law term, while the long-time non-exponential decay is due to the fact that the system energy spectrum has a lower bound. Increasing the barrier strength will greatly increase the probability of particles remaining in the well.&lt;/sec&gt;&lt;sec&gt;For multiple potential barriers, the reflection and transmission of particles between the potential barriers interfere with each other. When the strength of the potential barrier is small, the particle still decays exponentially. For a larger potential barrier strength, the probability of particle reflection increases, and the particles that tunnel out may be bounced back. The survival probability oscillates sharply, reaching higher fidelity at certain moments. The oscillatory maximum of the survival probability decreases linearly with the number of barriers, while the moment corresponding to the oscillatory maximum shows a parabolic increase with the number of barriers. The introduction of a series disordered barriers can significantly improve the survival probability and greatly suppress its oscillations over time.&lt;/sec&gt;&lt;sec&gt;Our calculation is expected to find applications in quantum control of particle escape problem in the disordered system.&lt;/sec&gt;

Numerical study on mechanical properties of large diameter double-layer shield tunnels under the elevated temperatures in fire

As the development of underground engineering, shield tunnels in single-pipe and double-deck type have been widely used and promoted to improve the utilization rate of the effective space. For this complex structure, fire may trigger tunnel lining structure damage or even the failure of the structure. In this paper, the mechanical properties of a large diameter double-layer shield tunnel under elevated temperatures induced by fire were analyzed numerically. A thermo-mechanical coupling numerical approach was employed to implement the thermo-mechanical models in full size. Aiming at a large-diameter shield tunnel with the internal structure combining road and metro space in Jinan, China, the model is applied in a parametric study to verify the fire resistance of tunnel structures under different configurations and RABT fire exposure. The effects of the internal structure and fire location on the complicated mechanical properties of the tunnel were analyzed. Results from numerical analysis showed that the elevated temperatures have a significant impact on the mechanical properties of tunnel, and the structure subjected to elevated temperatures has obvious expansion deformation and stress change. The internal structure has a great influence on the mechanical properties of the tunnel under elevated temperatures, which is conducive to reducing the radial convergence deformation of the tunnel lining structure and improving the internal force state of the lining structure. The location of the fire in the tunnel has a major influence on the internal force and deformation of the tunnel structure. When the fire occurs in the lower space of the tunnel, the fire safety of the internal box culvert structure should be paid more attention. The key design considerations have been identified as the concrete deck slab and the tunnel lining segmental joints configuration.

Mechanical-characteristic evaluation of excavation unloading rock mass subject to high-temperature conditions

Recently, the frequency of highway tunnel fire has been increasing annually, which necessitates attention toward the stability and safety of surrounding rocks in the unlined tunnels exposed to fires. This study aimed to investigate the influence of the high temperature of excavation unloading on the physical and mechanical properties of unlined tunnel surrounding rock that has been exposed to fire erosion and tunnel ventilation. To this end, granite specimens that had undergone hierarchical unloading tests were selected as the research object, and high temperature and triaxial reloading tests were carried out on unloading-damaged specimens. The variation of mechanical properties and failure characteristics of unloading-damaged specimens with temperature was analyzed, and the differences in their mass, wave velocity, magnetic properties and apparent characteristics under the influence of high temperatures were compared. The results are as follows: (1) The mechanical properties of the unloading-damaged specimens deteriorate obviously under high temperatures, and the greater the temperature, the higher is the reduction in the sample peak strength; there is an obvious nonlinear relationship between them when the unloading-damaged specimens are reloaded after being exposed to a high temperature, and there is a certain threshold for the reduction of mechanical strength of the specimens due to temperature. (2) During triaxial reloading, the pre-peak strain is not related to the confining pressure, but the post-peak strain is closely related to the unloading confining pressure. The higher the temperature, the greater the post-peak accelerated strain. (3) The unloading effect provides a channel for the high temperature to change the physical and mechanical characteristics of the parent rock. The unloading-damaged specimens are gray white at 25 ℃, gray brown at 300 ℃, and reddish brown at 600 ℃. The results show that the wave velocity of the unloading damage specimen decreases slightly at 300 ℃, but significantly at 600 ℃, with an average decrease of 64.73%. (4) The thermal load intensifies the crack evolution, expansion, and structural relaxation of the unloading-damaged specimens, and the unloading magnitude and temperature change the distribution of the dominant fracture surface of the specimens. The confining pressure plays a dominant role in the deformation and failure of the specimens at low temperatures, while thermal load dominates at high temperatures. The research results can provide a theoretical reference for the engineering design of unlined tunnels with surrounding rocks.

Study on the Mechanical Properties of Hydraulic Tunnels With High Ground Temperature and the Temporal and Spatial Evolution of Plastic Zone

In order to explore the temporal and spatial evolution of the mechanical characteristics of hydraulic tunnels with high ground temperature during construction, a numerical simulation study was performed on the construction process of the tunnel using finite element calculation software, and the results were compared with the field monitoring results. The results showed that the displacements of the top arch and waist arch of the tunnel increased with time, and the top arch of the tunnel entrance was greatly affected by the excavation. The plastic zone was larger in the top arch and the bottom arch of surrounding rock, and smaller in the waist arch. The plastic strain of the top arch and bottom arch of surrounding rock was smaller, while the plastic strain of the waist arch was larger. The parallel excavation and lining construction have less impact on the surrounding rock.