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Construction strategies for a NATM tunnel in Sao Paulo, Brazil, in residual soil

Underground Space 2022年第1期7卷 1-18页

作者： Osvaldo P.M.Vitali Tarcisio B.Celestino antonio bobet Lyles School of Civil Engineering Purdue UniversityWest LafayetteIN 47907USA Sao Carlos School of Engineering University of Sao PauloSao CarlosSP 13566Brazil

Due to the fast growth of urban areas worldwide,the demand for tunnels in developed areas is increasing.The design and construc-tion of those tunnels are complex because of their shallow depths and their interaction with existing aboveground and buried structures,which results in rather limited allowable ground deformations induced by the tunnel excavation and support.In tropical regions,residual porous soils near the surface are common.Those soils are highly deformable;thus,tunneling may induce large ground deformations that may damage nearby structures.The new Austrian tunneling method(NATM)and the sprayed concrete lining(SCL)technique are being widely employed in several big cities in tropical regions,but little research has been conducted to assess the induced ground deformations in residual soils,common in tropical areas.This paper provides insight into this issue.A well-documented metro tunnel in Sa˜o Paulo,Brazil,in a residual red porous clay,was analyzed using 3D finite element method(FEM).The behavior of the residual red porous clay was approximated by an advanced constitutive soil model calibrated with triaxial tests on intact samples extracted at the site.Predictions of the tunnel deformations during construction matched the field data.The calibrated model was then used to explore the tunnel per-formance under different construction strategies.The influence of partial face excavation,unsupported span length,support stiffness and pipe roof umbrella were assessed.The numerical results showed that partial face excavation was effective to reduce ground deformations ahead of the face of the tunnel and to improve face stability;however,the settlements behind the face increased because of the delay in closing the primary lining.The installation of a stiffer liner closer to the face reduced the ground deformations significantly.The pipe roof umbrella was the most effective technique to reduce the ground deformations around the tunnel;however,the numerical results did not consider deformations that could be ind

关键词： Tunnel NATM Residual soil FEM 3D face effects Ground deformation Face stability

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Effect of frequency and flexibility ratio on the seismic response of deep tunnels

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Underground Space 2017年第2期2卷 125-133页

作者： Eimar Sandoval antonio bobet Lyles School of Civil Engineering Purdue UniversityWest Lafayette 47906United States School of Civil Engineering and GeomaticsUniversidad del ValleCaliColombia

Two-dimensional dynamic numerical analyses have been conducted,using FLAC 7.0,to evaluate the seismic response of underground structures located far from the seismic source,placed in either linear-elastic or nonlinear elastoplastic ground.The interaction between the ground and deep circular tunnels with a tied interface is considered.For the simulations,it is assumed that the liner remains in its elastic regime,and plane strain conditions apply to any cross section perpendicular to the tunnel axis.An elastoplastic constitutive model is implemented in FLAC to simulate the nonlinear ground.The effect of input frequency and relative stiffness between the liner and the ground,on the seismic response of tunnels,is evaluated.The response is studied in terms of distortions normalized with respect to those of the free field,and load demand(axial forces and bending moments)in the liner.In all cases,i.***.for linear-elastic and nonlinear ground models,the results show negligible effect of the input frequency on the distortions of the cross section,for input frequencies smaller than 5 Hz;that is for ratios between the wave length and the tunnel opening(k=D)larger than ten for linear-elastic and nine for nonlinear ground.Larger normalized distortions are obtained for the nonlinear than for the linear-elastic ground,for the same relative stiffness,with differences increasing as the tunnel becomes more flexible,or when the amplitude of the dynamic input shear stress increases.It has been found that normalized distortions for the nonlinear ground do not follow a unique relationship,as it happens for the linear-elastic ground,but increase as the amplitude of the dynamic input increases.The loading in the liner decreases as the structure becomes more flexible with respect to the ground,and is smaller for a tunnel placed in a stiffer nonlinear ground than in a softer nonlinear ground,for the same flexibility ratio.

关键词： Deep circular tunnel Dynamic numerical analysis Flexibility ratio Distortion Seismic response

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Seismic distortions of a deep circular tunnel in elastic slightly anisotropic ground

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Underground Space 2017年第2期2卷 134-147页

作者： antonio bobet Haitao Yu Lyles School of Civil Engineering Purdue UniversityWest LafayetteIN 47907USA High-End Foreign Expert at Tongji University Shanghai 200092China Key Laboratory of Geotechnical and Underground Engineering of Ministry of Education Tongji UniversityShanghai 200092China State Key Laboratory for GeoMechanics and Deep Underground Engineering China University of Mining and TechnologyBeijing 100083China

Tunnels must withstand not only the demands stemming from normal working conditions but also from extreme events such as earthquakes.Indeed,there is consistent evidence in the technical literature that indicates that tunnels are vulnerable to damage and must be designed to adequately support the demand imposed by the earthquake.Such demand should be estimated using dynamic numerical methods that include soil-structure interaction and incorporate realistic models for the support and surrounding ground.For preliminary analysis,however,or when the seismic demand is insufficient to take the ground beyond its elastic regime,analytical solutions may provide a reasonable estimate of the tunnel behavior,especially if the tunnel is sufficiently far from the seismic source such that a pseudostatic analysis is acceptable.Most analytical solutions are based on the assumption that the ground is isotropic,which may not be realistic,as e.***.depositional processes may result in engineering properties that depend on the direction of deposition.The work presented in the paper builds on the results by bobet(2011,2016)who provided closed-form solutions for deep tunnels in elastic transversely anisotropic ground;however,the paper provides much simpler solutions for those cases where the ground is slightly anisotropic.A comparison between the approximate and the exact solutions shows that the errors are negligible when the ground anisotropy is small and grow,albeit slowly,as the ground anisotropy increases.The conclusion applies to different loading conditions,drained and undrained,and to different ground-support interfaces,tied or frictionless.

关键词： Seismic behavior Deep tunnel Transversely anisotropic ground Drained and undrained loading

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Seismic analysis of long tunnels:A review of simplified and unified methods

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Underground Space 2017年第2期2卷 73-87页

作者： Haitao Yu Yong Yuan antonio bobet Key Laboratory of Geotechnical and Underground Engineering of Ministry of Education Tongji UniversityShanghai 200092China State Key Laboratory for GeoMechanics and Deep Underground Engineering China University of Mining and TechnologyBeijing 100083China State Key Laboratory of Disaster Reduction in Civil Engineering Tongji UniversityShanghai 200092China High-End Foreign Expert at Tongji University Shanghai 200092China Lyles School of Civil Engineering Purdue UniversityWest LafayetteIN 47907USA

Seismic analysis of long tunnels is important for safety evaluation of the tunnel structure during earthquakes.Simplified models of long tunnels are commonly adopted in seismic design by practitioners,in which the tunnel is usually assumed as a beam supported by the ground.These models can be conveniently used to obtain the overall response of the tunnel structure subjected to seismic loading.However,simplified methods are limited due to the assumptions that need to be made to reach the solution,e.***.shield tunnels are assembled with segments and bolts to form a lining ring and such structural details may not be included in the simplified model.In most cases,the design will require a numerical method that does not have the shortcomings of the analytical solutions,as it can consider the structural details,non-linear behavior,etc.Furthermore,long tunnels have significant length and pass through different strata.All of these would require large-scale seismic analysis of long tunnels with three-dimensional models,which is difficult due to the lack of available computing power.This paper introduces two types of methods for seismic analysis of long tunnels,namely simplified and unified methods.Several models,including the mass-spring-beam model,and the beam-spring model and its analytical solution are presented as examples of the simplified method.The unified method is based on a multiscale framework for long tunnels,with coarse and refined finite element meshes,or with the discrete element method and the finite difference method to compute the overall seismic response of the tunnel while including detailed dynamic response at positions of potential damage or of interest.A bridging scale term is introduced in the framework so that compatibility of dynamic behavior between the macro-and meso-scale subdomains is enforced.Examples are presented to demonstrate the applicability of the simplified and the unified methods.

关键词： Earthquake engineering Tunnel structure Seismic analysis Simplified method Multiscale method

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3D finite element modelling optimization for deep tunnels with material nonlinearity

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Underground Space 2018年第2期3卷 125-139页

作者： Osvaldo P.M.Vitali Tarcisio B.Celestino antonio bobet Lyles School of Civil Engineering Pwrdue UniversityWest LafayetteIN 47907USA Sao Carlos School of Engineering.Univerity of Sao Paulo Sao CarlosSP 13566Brazil

3D modeling of tunnels using a nonlinear ground model is still a time-consuming task because it usually requires a large number of incremental phases with iterative processes,to ensure accuracy while minimizing computational effort.Optimization of theﬁnite element mesh is of utmost importance.Despite the current tendency towards 3D modeling of tunnels,few publications are concerned with mesh optimization considering model size,grid reﬁnement and order of elements.This paper improves the understanding of key issues that affect 3D modeling of tunnels.Our results shown that:(1)2nd order elements are more effcient when material nonlinearity is present and should be preferred;(2)the plastic zone size has a strong inﬂuence on the model dimensions and may require discretizations much larger than those currently accepted.The paper provides recommendations for mesh reﬁnement and model dimensions(width and length)as a function of the plastic zone size,for accurate 3D models with reduced computational cost.

关键词： Tunnel Numerical modeling Finite element method Mesh optimization Nonlinear material

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Behavior of tunnels excavated with dip and against dip

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Underground Space 2021年第6期6卷 709-717页

Rock masses with remarked rock structure are likely to be highly anisotropic;thus,the relative orientation of the tunnel with respect to the rock structure will affect the tunnel behavior.Displacements measured at the walls of tunnels in highly anisotropic rock masses often reveal an asymmetric deformation pattern around the tunnel perimeter,which is often interpreted as the result of rock heterogeneity or changing geology.However,numerical and analytical investigation of tunnels in anisotropic rock masses show that the tunnel axis misalignment with the principal directions of stress and material anisotropy induce anti-symmetric axial displacements(i.e.,axial distortion of the tunnel cross section)far behind the tunnel face.Near the face,the axial distortion is partially constrained,causing asymmetric radial displacements.In this study,tunnels excavated with and against dip of the major rock mass discontinuity are explored using 3D FEM modeling.A detailed analysis on the mechanisms associated with the direction of excavation is provided.It is shown that the asymmetric displacements near the face may strongly affect the displacements measured at the tunnel walls,which may explain the asymmetric displacements commonly observed on tunnels in anisotropic rock.

关键词： Tunnel Tunnel misalignment Anisotropic rock Face effects

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Effect of temperature on deep lined circular tunnels in transversely anisotropic elastic rock

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Underground Space 2016年第2期1卷 79-93页

作者： Tao Fei bobet antonio Lyles School of Civil Engineering Purdue UniversityWest LafayetteINUSA Department of Geotechnical Engineering Tongji UniversityShanghaiChina

Considerably less attention has been given to thermal stresses in a tunnel.Temperature changes in the ground or inside the tunnel,e.***.due to fire,can cause cracking and damage to the liner and surrounding ground.This study derived analytical solutions for stresses and displacements caused by thermal load for a lined circular tunnel under a transversely anisotropic ground where the ground anisotropy axis coincides with the stacking direction.The FEM code ABAQUS was used to study a lined deep tunnel when the ground anisotropy axis is perpendicular to the stacking direction.A parametric study was performed to investigate the effects of Young’s modulus,Poisson’s ratio,thermal conductivity and the coefficient of thermal expansion on the behavior of the liner and ground.The results show that the Young’s modulus and the coefficient of thermal expansion are the most important parameters that determine the stresses and displacements of the liner and ground.The analysis also shows that the thermal conductivity has a significant effect on the temperature distribution in the ground.

关键词： Deep tunnel Circular liner Transversely anisotropic ground Thermal stresses

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Integrating Levels of Hierarchical Organization in Porous Organic Molecular Materials

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Nano-Micro Letters 2024年第5期16卷 134-153页

作者： Jesus Ferrando‑Soria antonio Fernandez Instituto de Ciencia Molecular(ICMol) Universidad de Valencia46980 ValenciaSpain School of Science Loughborough UniversityLoughborough LE113TUUK

Porous organic molecular materials(POMMs)are an emergent class of molecular-based materials characterized by the formation of extended porous frameworks,mainly held by non-covalent interactions.POMMs represent a variety of chemical families,such as hydrogen-bonded organic frameworks,porous organic salts,porous organic cages,C-H···πmicroporous crystals,supramolecular organic frameworks,π-organic frameworks,halogen-bonded organic framework,and intrinsically porous molecular materials.In some porous materials such as zeolites and metal organic frameworks,the integration of multiscale has been adopted to build materials with multifunctionality and optimized properties.Therefore,considering the significant role of hierarchy in porous materials and the growing importance of POMMs in the realm of synthetic porous materials,we consider it appropriate to dedicate for the first time a critical review covering both topics.Herein,we will provide a summary of literature examples showcasing hierarchical POMMs,with a focus on their main synthetic approaches,applications,and the advantages brought forth by introducing hierarchy.

关键词： Porous organic molecular materials Hierarchy Hydrogen-bonded organic frameworks Porous cages Fullerene

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Cost-effective synthesis of giant molecule acceptors(GMAs)for stable polymer solar cells

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Science China Chemistry 2024年第4期67卷 1041-1043页

作者： antonio Facchetti Department of Chemistry and the Materials Research Center Northwestern University2145 Sheridan Road60208 EvanstonIllinoisUSA School of Materials Science and Engineering Georgia Institute of Technology771 Ferst Drive30332 AtlantaGeorgiaUSA

Polymer solar cells(PSCs)have emerged as a disruptive energy technology due to simple device architecture,earthabundant elemental composition,lightweight nature,and inherent mechanical flexibility[1,2].Via a strategic acceptordonor-acceptor(A-D-A)design of small-molecule acceptors(SMAs),device power conversion efficiency(PCE)has now increased>19%.

关键词： acceptor synthesis donor

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SARS-CoV-2 immunity

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Cellular & Molecular Immunology 2024年第2期21卷 101-102页

作者： antonio Bertoleti Program in Emerging Infectious Diseases Duke-NUS Medical SchoolSingaporeSingapore

Four years have swiftly passed since the identification of a novel coronavirus from patients with pneumonia that signs the start of the COVID-19 pandemic[1].The world's social and economic landscape has largely reverted to its prepandemic state,and different issues unrelated to the pandemic are currently impacting various regions globally.The scientific community,which quickly modified its research focus during the initial years of the pandemic to generate a wealth of scientific data that helped in understanding and controlling SARS-CoV-2 infection,is also facing a new phase in the study of virus-host interactions.

关键词： immunity globally landscape

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