Tunnel Shapes Research Articles

Critical Face Pressure of a Tunnel Driven by a Shield Machine Considering Seismic Forces and Tunnel Shape Influence

Evaluating critical face pressure with high accuracy is an important topic for shield tunneling. The existing research focuses more on the influence of complex geological conditions or environmental factors, and there are few reports on the influence of tunnel shape on critical face pressure. In reality, the tunnel shape has a significant impact on the deformation zone in front of the tunnel face, which may lead to non-negligible differences in shield pressure. To fill this gap, an efficient analytical approach is proposed to estimate the critical face pressure considering different tunnel shapes in the framework of limit analysis. As earthquakes are potential threats to the tunnel face stability in seismically active regions, the seismic effect is also taken into account with the help of the pseudo-static method. Several cases with the same area but different tunnel shapes are investigated using the limit analysis method. A comparison with static analysis is given to highlight the influence of seismic forces on the tunnel face stability. The results show that the critical face pressures increase by 15.3% when the tunnel face shape changes from rectangular to circular, and by 23.5% when the horizontal seismic coefficient varies from 0 to 0.1. A further validation with a 3D finite difference method is performed with respect to four typical tunnel shapes considered in this study. Lastly, several stability charts are provided for a quick estimation of the critical tunnel face pressure subjected to seismic forces. It is concluded that the proposed method can be applied to a tunnel stability assessment of various cross-sections and is highly efficient compared with numerical simulations.

Time-dependent analytical solutions for tunnels excavated in anisotropic rheological rock masses

The anisotropy combined with the time-dependency of rock mass is commonly observed in tunnel construction. In this study, a comprehensive analytical investigation is performed on analysing time-dependent ground responses induced by tunnel excavation in an anisotropic rheological rock mass.An innovative analytical solution for the anisotropic viscoelastic problems is first proposed, which can be applied to the general cases that the rheological behaviours in anisotropic principal directions are independent and arbitrary. Using the generalized corresponding principle, the analytical model, which can precisely and rapidly address the problem, is then presented for the deformation and stresses around tunnels in transversely isotropic viscoelastic rock mass, considering different viscoelastic characteristics, different anisotropic angles, and circular/elliptical tunnel shapes. The analytical solutions agree very well with the numerical predictions for the consistent models, and can also be reduced to the isotropic viscoelastic case. Furthermore, the application of analytical solutions in practical engineering is validated by the good agreements between analytical solutions and field measurements. A parametric analysis is then performed to investigate the time-dependency of stress, and the effects of anisotropy ratios and anisotropy angles on displacements and stresses.The proposed analytical solution has a valuable contribution to the field of rock rheological mechanics, as it offers a benchmark for anisotropic viscoelastic problems, insights into the complex behaviour of anisotropic rock masses and provides a more accurate prediction of the ground response that may be useful to optimize the design of tunnel excavation in anisotropic rock masses.

Deformations and damages of tunnels subjected to strike-slip faulting: Effects of tectonic stress and cross-sectional shape

Deep-buried tunnels are vulnerable to strike-slip faulting, the responses of which are complicated. However, the effects of tectonic stress and cross-sectional shape on behaviors of tunnels in strike-slip faults have not been detailly investigated. This study performs numerical modeling to study the deformations and damages of tunnels subjected to strike-slip faulting, focusing on the effects of tectonic stress and cross-sectional shape. A three-dimensional numerical model is applied, which is validated by the test from the previous study. Different lateral stress coefficients (from 0.5 to 3.0) and cross-sectional shapes of tunnels (circular shape, horseshoe shape, and egg shape) are modeled. The results show that tectonic stress and cross-sectional shape have a great influence on tunnel responses during strike-slip faulting. The failure mode of the tunnel is highly dependent on the tectonic stress. The tensile damage controls in low tectonic stress conditions, while compressive damage domains in high tectonic stress conditions. The tensile damage initials at the arch waist in the vicinities of fault planes, while the compressive damage mainly occurs at the tunnel vault and bottom in the whole fracture zone. Besides, tectonic stress has apparent effects on the transverse displacement of the tunnel axis and the compressive damage range. The H-shaped tunnel behaves the worst, experiencing the largest cross-sectional deformation, the largest compressive damage range, and the smallest required fault deformation for compressive damage.

Shadowing effect of an existing tunnel on the evolution of soil arching: impact of tunnel shape

This study evaluates the shadowing effect of existing tunnels on the evolution of soil arching, focusing on the shape of the tunnel (circular and rectangular) through trapdoor experiments. The displacement and shear strain distributions of ground soil resulting from trapdoor movement were estimated using a digital image correlation technique. The results showed that the shadowing effect of the rectangular tunnel was significantly greater than that of the circular tunnel of the same size. The sand above the tunnel was displaced in a double-groove pattern owing to the presence of the tunnel, and the maximum surface settlement occurred between the tunnel boundary and the trapdoor edge. The circular tunnels exhibited consistently higher maximum surface displacements than that in the rectangular tunnels. The shear strain value of soil was lower for the rectangular tunnel case than that for the circular tunnel case. The rectangular tunnels required lesser trapdoor displacement than that of the circular tunnel to obtain the minimum soil arching ratio. The minimum and ultimate soil arching ratios increased as the burial depth ratio increased for both the tunnel shapes. The maximum stress ratio of the tunnel crown was consistently larger for the circular case than for the rectangular case.

Study on the influence of cross-section shape on the characteristics of wind flow field in heavy-daty railway tunnel

In order to reduce the coal dust pollution when the heavy train enters the tunnel and to ensure the safety of railroad operation, this paper adopts numerical simulation to study the characteristics of the wind flow field of the heavy train passing through different shapes of tunnels. The results show that the shape of the tunnel section has a significant effect on the piston wind characteristics of the train entering the tunnel. When the train passes through the tunnel, the value of the wind pressure and the gradient of the pressure on the surface of the carriages increase from horseshoe shape, high wall shape and high arch shape. The vortex structure generated at the entrance of the horseshoe tunnel is the smallest and the flow field is more stable, and the wind turbulence shows significant weakening effect; when the rear end of the car enters the tunnel, the range of the influence of the piston winds outside the tunnel is in order of smallest to largest for the horseshoe, high wall, and high arch tunnels; in the wake region, the central region of the strong vorticity zone in the horseshoe tunnel is more continuous, reducing the instability of the airflow in the tunnel. The results of this study are of great significance in understanding the characteristics of the wind flow field and the effect on dust generation when heavy trains pass through the tunnel.

Structure-Guided Steric Hindrance Engineering of Devosia Strain A6-243 Quinone-Dependent Dehydrogenase to Enhance Its Catalytic Efficiency.

Deoxynivalenol (DON), the most widely distributed mycotoxin worldwide, causes severe health risks for humans and animals. Quinone-dependent dehydrogenase derived from Devosia strain A6-243 (DADH) can degrade DON into less toxic 3-keto-DON and then aldo-keto reductase AKR13B3 can reduce 3-keto-DON into relatively nontoxic 3-epi-DON. However, the poor catalytic efficiency of DADH made it unsuitable for practical applications, and it has become the rate-limiting step of the two-step enzymatic cascade catalysis. Here, structure-guided steric hindrance engineering was employed to enhance the catalytic efficiency of DADH. After the steric hindrance engineering, the best mutant, V429G/N431V/T432V/L434V/F537A (M5-1), showed an 18.17-fold increase in specific activity and an 11.04-fold increase in catalytic efficiency (kcat/Km) compared with that of wild-type DADH. Structure-based computational analysis provided information on the increased catalytic efficiency in the directions that attenuated steric hindrance, which was attributed to the reshaped substrate-binding pocket with an expanded catalytic binding cavity and a favorable attack distance. Tunnel analysis suggested that reshaping the active cavity by mutation might alter the shape and size of the enzyme tunnels or form one new enzyme tunnel, which might contribute to the improved catalytic efficiency of M5-1. These findings provide a promising strategy to enhance the catalytic efficiency by steric hindrance engineering.

Structural insights of poly(butylene adipate-co-terephthalate) depolymerases

Poly (butylene adipate-co-terephthalate), PBAT, is one of the most popular plastics nowadays and is becoming a large burden to the environment when PBAT waste is accumulated. Biodegradation of PBAT is an environmentally friendly method to treat PBAT waste. In the past two decades, a couple of microbial strains or mixed strains have been chemically characterized. From this, many PBAT depolymerases have been isolated and further structurally determined. The review we focused on the PBAT depolymerases that have been structurally characterized, including lipases, esterases, and cutinases. We also discussed which shape of the substrate-binding tunnels is beneficial for recognizing and decomposing polymer chains of PBAT, which would be important guidance in directing the designation of PBAT depolymerases.

Optimum design parameters for a venturi-shaped roof to maximize the performance of building-integrated wind turbines

Venturi-shaped roofs provide advantageous wind conditions for efficiently operating building-integrated wind turbines without losing usable floor area. Despite these advantages, venturi-shaped roofs have been sparsely adopted for buildings due to the lack of understanding of their optimum designs to maximize the performance of building-integrated wind turbines. For the first time in literature, this study investigated four design parameters: support structure, corner modification, tunnel shape, and wind turbine arrangement to estimate the optimum venturi-shaped roof design by conducting Computational Fluid Dynamics (CFD) simulations. The results revealed the advantages of shorter support structures with convex and concave shapes at upwind and downwind ends, creating high wind speeds with low turbulence intensities. Corner modifications to the tunnel's entrance and exit are vital to suppress flow separation at the tunnel's entrance and uniform distributions of wind speed and pressure. This study recommends aerodynamic tunnel shapes that follow a non-uniform rational B-spline (NURBS) to accelerate wind without increasing turbulence intensities. The optimum design parameters performed better in normal and oblique wind directions, confirming their universal applicability. This study proposes integrating all optimum design parameters into a venturi-shaped roof design to alleviate the adverse effects of support structures, which are essential for a stable roof design.

A Numerical Study on the Effect of Different Tunnel Shapes in Squeezing Rocks

A Numerical Study on the Effect of Different Tunnel Shapes in Squeezing Rocks

A Method for Convergent Deformation Analysis of a Shield Tunnel Incorporating B-Spline Fitting and ICP Alignment

The application of three-dimensional laser scanning technology in the field of tunnel deformation monitoring has changed the traditional measurement method. It provides an automated and intelligent solution for monitoring the geometric deformation of tunnel sections due to its high efficiency and independence from environmental influences. In this paper, based on B-spline fitting and iterative nearest point (ICP) alignment, the calculation of the difference between the radial distance and the design radius of a tunnel is transformed into a curve transformation that iterates over the nearest-neighbor points and calculates the difference in the distance between the corresponding points. The innovation of this paper is that the high-precision tunnel deformation monitoring method integrating B-spline fitting and ICP alignment can automatically compensate for the missing point clouds, is not affected by the point clouds of the tunnel inner and outer liner appendages, is more sensitive in the local deformation feedback and can be applied to a variety of tunnel shapes. The results indicate that our method maximally improves the accuracy of the horizontal convergence calculation by 28.6 mm and the accuracy of the vault settlement by 27.8 mm in comparison with the least squares circle fitting algorithm.

Dynamic analysis of precast ultra-high performance concrete tunnel under internal explosion

Underground structures hold great significance in the infrastructure of modern society. With the rapid construction of such facilities, the possibility of explosions occurring inside these structures due to unforeseen accidents or deliberate acts cannot be ignored. Past catastrophic events have demonstrated the necessity of implementing anti-blast design for underground structures, particularly in vulnerable locations. This promotes investigations into the behavior of underground structures subjected to internal explosions. For the first time, a thorough simulation model is developed using the multi-material Coupled Eulerian–Lagrangian approach to examine a full-scale precast ultra-high performance concrete (UHPC) tunnel under internal explosion. The precast tunnel structure closely resembles real construction configurations. The simulation model takes into account the simultaneous interaction between the tunnel and the surrounding soil. The accuracy of the suggested simulation model is validated against experimental results. For various explosive charge weights, tunnel lining thicknesses, materials, and tunnel shapes, extensive parametric simulations are conducted. Results obtained highlighted UHPC's superiority as a substitute for conventional concrete due to its strong blast-resistant capacity. The findings from this research also shed light on the precast UHPC tunnel's structural response to an interior explosion, that can assist designers and managers choose the best design for blast protection.

Determination of minimum overburden depth for underwater shield tunnel in sands: Comparison between circular and rectangular tunnels

With the development of global urbanization, the utilization of underground space is more critical and attractive for civil purposes. Various shapes of shield tunnels have been gradually proposed to cope with different geological conditions and service purposes of underground structures. Generally, reducing the burial depth of shield tunnel is conducive to construction and cost saving. However, extremely small overburden depth cannot provide sufficient uplift resistance to maintain the stability and serviceability of the tunnel. To this end, this paper firstly reviewed the status of deriving the minimum sand overburden depth of circular shield tunnel using mechanical equilibrium (ME) method. It revealed that the estimated depth is rather conservative. Then, the uplift resistance mechanism of both circular and rectangular tunnels was deduced theoretically and verified with the model tests. The theoretical uplift resistance is consistent with the experimental values, indicating the feasibility of the proposed equations. Furthermore, the determination of the minimum soil overburden depth of rectangular shield tunnel under various working conditions was presented through integrated ME method, which can provide more reasonable estimations of suggested tunnel burial depth for practical construction. Additionally, optimizations were made for calculating the uplift resistance, and the soil thickness providing uplift resistance is suggested to be adjusted according to the testing results. The results can provide reference for the design and construction of various shapes of shield tunnels in urban underground space exploitation.

Analytical stress and displacement of twin noncircular tunnels in elastic semi-infinite ground

In general, twin noncircular tunnels may cause high stress concentrations and large settlements because of the strong interaction between tunnels and their noncircular shape. In this study, new analytical solutions are presented to efficiently predict the elastic stresses and displacements around shallow twin noncircular tunnels in rocks. The key factors, i.e., the real interactions between tunnels, arbitrary tunnel shapes, arrangements and pressures exerted at the internal tunnel boundaries due to liners or water pressures, are fully taken into account.The Schwartz alternating method is used to reduce the twin noncircular tunnels problem to a series of problems where only one noncircular tunnel is contained in the half-plane. Then, the solutions to the problem of a noncircular tunnel in the half-plane are obtained by complex variable theory combined with conformal mapping. Finally, convergent and highly accurate analytical solutions of twin noncircular tunnels are achieved by superposing the solutions of the reduced single tunnel problems. The analytical solutions are verified by the good agreement between the analytical and FEM results under the same assumptions. The proposed analytical solution can help to reveal the mechanical mechanisms of ground responses due to twin tunnelling in an elastic semi-infinite ground.

Analytical Solution to the Seepage Field of Two Parallel Noncircular Tunnels in Permeable Anisotropic Ground

This paper provides an analytical solution and solving procedure for the seepage field around two noncircular tunnels in anisotropic permeable ground. The anisotropic problem is first made equivalent to an isotropic problem by coordinate transformation. Then, by using Schwartz alternate method and conformal mapping, a precise analytical solution is obtained based on the anisotropic problem of single tunnel with redundant hydraulic heads at tunnel boundary. The noncircular tunnel interaction and the permeable anisotropy are considered accurately. The iterative procedure is simple and efficient in its calculations, and achieves good convergence. The results of the analytical model are compared with the finite element results, and show good agreement. Finally, some parametric studies are present to research the influences of tunnel shapes and the anisotropic permeability ratio on the seepage field, and the effect of the location of the pilot tunnel on the seepage field of the primary tunnel is also investigated.

Producing Undrained Stability Factors for Various Tunnel Shapes

Producing Undrained Stability Factors for Various Tunnel Shapes

Prediction of the Stability of Various Tunnel Shapes Based on Hoek–Brown Failure Criterion Using Artificial Neural Network (ANN)

In this paper, artificial neural network (ANN) models are presented in order to enable a prompt assessment of the stability factor of tunnels in rock masses based on the Hoek–Brown (HB) failure criterion. Importantly, the safety assessment is one of the serious concerns for constructing tunnels and requires a reliable and accurate stability analysis. However, it is challenging for engineers to construct finite element limit analysis (FELA) algorithms with the HB failure criterion for tunnel stability solutions in rock masses. For the first time, a machine-learning-aided prediction of tunnel stability based on the HB failure criterion is proposed in this paper. Three different shapes of tunnels, i.e., heading tunnel, dual square tunnels, and dual circular tunnels, are considered. The inputs include four dimensionless parameters for the heading tunnel including the cover-depth ratio, the normalized uniaxial compressive strength, the geological strength index (GSI), and the mi parameter. Moreover, dual square and circular tunnels include one more additional parameter namely the distance ratio. The results present the best ANN models for each tunnel shape, providing very reliable solutions for predicting the tunnel stability based on the HB failure criterion.

Stress and displacement fields around an arbitrary shape tunnel surrounded by a multilayered elastic medium subjected to harmonic waves under plane strain conditions

This study focuses on the propagation of harmonic mechanical waves around both circular and non-circular tunnels. The excavation disturbed zone is explicitly modeled with a multilayered description of the surroundings of the tunnel. The purpose of this paper is thus to establish closed-form solutions for stress and displacement fields for circular and non-circular geometries taking into account the mechanical heterogeneity of the area adjacent to the tunnel. Particularly, the multilayered non-circular shape configuration is a great step not treated previously. The classical approach based on the wave function expansion method is used to determine the expressions of stresses and displacements around circular geometries. To handle non-circular tunnel shapes, the complex variable method based on the Muskhelishvili approach and conformal mapping functions is introduced. Results indicate that the excavation damaged zone strongly modifies the distribution of stress and displacement fields around the tunnel. Geometrical tunnel shapes also affect stress and displacement polar diagrams.

Towards replacing physical testing of granular materials with a Topology-based Model

In the study of packed granular materials, the performance of a sample (e.g., the detonation of a high-energy explosive) often correlates to measurements of a fluid flowing through it. The "effective surface area," the surface area accessible to the airflow, is typically measured using a permeametry apparatus that relates the flow conductance to the permeable surface area via the Carman-Kozeny equation. This equation allows calculating the flow rate of a fluid flowing through the granules packed in the sample for a given pressure drop. However, Carman-Kozeny makes inherent assumptions about tunnel shapes and flow paths that may not accurately hold in situations where the particles possess a wide distribution in shapes, sizes, and aspect ratios, as is true with many powdered systems of technological and commercial interest. To address this challenge, we replicate these measurements virtually on micro-CT images of the powdered material, introducing a new Pore Network Model based on the skeleton of the Morse-Smale complex. Pores are identified as basins of the complex, their incidence encodes adjacency, and the conductivity of the capillary between them is computed from the cross-section at their interface. We build and solve a resistive network to compute an approximate laminar fluid flow through the pore structure. We provide two means of estimating flow-permeable surface area: (i) by direct computation of conductivity, and (ii) by identifying dead-ends in the flow coupled with isosurface extraction and the application of the Carman-Kozeny equation, with the aim of establishing consistency over a range of particle shapes, sizes, porosity levels, and void distribution patterns.

Sub-Rectangular Tunnel Behavior under Seismic Loading

Circular and rectangular tunnel shapes are usually chosen when excavating at shallow depths in urban areas. However, special-shaped tunnels such as sub-rectangular tunnels have recently been used to overcome some drawbacks of circular and rectangular tunnels in terms of low space utilization efficiency and stress concentration, respectively. In the literature, experimental studies as well as analytical and numerical models have been developed for the seismic analysis and vulnerability assessment of circular and rectangular tunnels since the early 1990s. However, knowledge gaps regarding the behavior of sub-rectangular tunnels under seismic loading remain and still need to be bridged. The present paper focuses on introducing a numerical analysis of sub-rectangular tunnels under seismic loading. The numerical model of sub-rectangular tunnels is developed based on the numerical analyses of circular tunnels validated by comparing well-known, analytical solutions. This paper aims to highlight the differences between the behavior of sub-rectangular tunnels compared with circular tunnels when subjected to seismic loadings. Special attention is paid to the soil–lining interface conditions. The influence of parameters, such as soil deformations, maximum horizontal acceleration, and lining thickness, on sub-rectangular tunnel behavior under seismic loading is also investigated. The results indicate a significant behavior difference between sub-rectangular and circular tunnels. The absolute extreme incremental bending moments for a circular tunnel (no-slip condition) are smaller than that for the corresponding full-slip condition. The absolute extreme incremental bending moments of sub-rectangular tunnels (no-slip condition) are, however, greater than the corresponding full-slip conditions.

An Improved Form of 2D SPH Method for Modeling the Excavation Damage of Tunnels Containing Random Fissures

The excavation damage of deep tunnels is one of the most important factors contributing to the failure of tunnel structures. In order to investigate the influence of tunnel shapes and fissure geometries, the kernel function in the traditional SPH method has been improved, which can realize the brittle fracture characteristics of particles and can be called the Improved Kernel of Smoothed Particle Hydrodynamics (IKSPH-2D). Meanwhile, the random fissure generation method in IKSPH has been put forward. Different tunnel shapes, fissure geometries, and locations are considered during the simulation of tunnel excavation, and results show that (1) the typical “V”-shaped shear damage zones appear after the tunnel excavation, which is consistent with engineering practice. Meanwhile, tunnel excavation also has an “activating” effect on the preexisting fissures. (2) The stability of circular-shaped tunnel is the best, while horseshoe shaped tunnel is worse, and the “U”-shaped tunnel is the worst. (3) Fissures with small and large dip angles have the greatest influence on the stability of tunnel excavation. With the increase of fissure numbers and lengths, the tunnel tends to be instable. (4) The IKSPH method gets free from traditional grids in FEM, which can dynamically reflect the fracture processes of tunnel excavation. Meanwhile, developing 3D IKSPH parallel program will be the future directions.