Exploration on Defect Prevention and Maintenance Methods of Highway Tunnel Structure

Highway tunnel traffic safety is an important part of traffic safety.With the aging of tunnels,increase in traffic flow,changes in the operating environment and traffic accidents,the many problems started to occur in tunnels,affecting the operational and structural safety.In this paper,we summarize and analyze the types and causes of defects found in the process of tunnel maintenance at home and abroad,and propose corresponding suggestions for the current maintenance of the main structure of highway tunnels.

K-modified MnO_(δ)catalysts with tunnel structure and layered structure:Facile preparation and catalytic performance for soot combustion

Air pollution from particulate matter produced by incomplete combustion of diesel fuel has become a serious environmental pollution problem,which can be addressed by catalytic combustion.In this work,a series of K-modified MnO_(δ)catalysts with different microstructures were synthesized by the hydrothermal method,the relationship between structure of the catalysts and their catalytic performance for soot combustion was studied by characterization techniques and density functional theory(DFT)calculations.Results showed that the prepared catalysts had good catalytic performance for soot combustion and could completely oxidize soot at temperatures below 400℃.The cryptomelane-type K_(2−x)Mn_(8)O_(16)(K-OMS-2)with tunnel structure had excellent NO oxidation capacity and abundance of Mn^(4+)ions(Mn^(4+)/Mn^(3+)=1.24)with good redox ability,it demonstrated better soot combustion performance than layered birnessite-type K_(2)Mn_(4)O_(8)(K-OL-1).The T_(10),T_(50),T_(90)temperatures of KOMS-2 were 269,314,346℃,respectively.The K-OMS-2 catalyst also showed excellent stability after five catalytic cycles,with T_(10),T_(50),T_(90)values holding in the ranges of 270±2,316±2,348±3℃,respectively.

Long-term mechanical analysis of tunnel structures in rheological rock considering the degradation of primary lining

Rock load on lining structures increases over time for tunnels buried in rheological rock,and in addition deterioration of primary lining is common due to its structural characteristics and service environment attack,where these delayed features affect the mechanical response of tunnels.However,accounting for these delayed features in long-term stability assessment of tunnel structures is complex and has not attracted enough attention.In this paper,an analytical approach is proposed for investigating long-term mechanical response of tunnel structures in rheological rock influenced by degradation of primary lining.For this purpose,degradation of primary lining,char-acterized by decreasing concrete stiffness over time,is quantitatively described by an exponential model.The rheological characteristic of surrounding rock is simulated by the Burgers model.The time-varying solutions for rock deformation and support pressure are obtained by considering the coordinated interaction between surrounding rock and linings,and their correctness is verified by comparing them with numerical results.The results revealed that the pressure imposed on linings due to the rheological behavior of surrounding rock increases over time.As the primary lining degrades,the rheological load is transferred from primary lining to secondary lining,leading to increasing pressure on secondary lining;and a faster degradation rate of primary lining leads to greater pressure on secondary lining.Therefore,the primary lining should not be overlooked in long-term safety assessment of operation tunnels because of its role in bearing and transmitting load.Finally,the tunnel’s design and operational maintenance strategy are discussed when the delay effects of surround-ing rock and lining are taken into account.

A multi-purpose prototype test system for mechanical behavior of tunnel supporting structure: Development and application

A multi-purpose prototype test system is developed to study the mechanical behavior of tunnel sup-porting structure,including a modular counterforce device,a powerful loading equipment,an advanced intelligent management system and an efficient noncontact deformation measurement system.The functions of the prototype test system are adjustable size and shape of the modular counterforce structure,sufficient load reserve and accurate loading,multi-connection linkage intelligent management,and high-precision and continuously positioned noncontact deformation measurement.The modular counterforce structure is currently the largest in the world,with an outer diameter of 20.5 m,an inner diameter of 16.5 m and a height of 6 m.The case application proves that the prototype test system can reproduce the mechanical behavior of the tunnel lining during load-bearing,deformation and failure processes in detail.

Numerical Analysis of Three-Layer Deep Tunnel Composite Structure

To date,with the increasing attention of countries to urban drainage system,more and more regions around the world have begun to build water conveyance tunnels,sewage pressure deep tunnels and so on.However,the sufficient bearing capacity and corrosion resistance of the structure,which can ensure the actual service life and safety of the tunnel,remain to be further improved.Glass Fiber Reinforced Plastics(GFRP)pipe,with light weight,high strength and corrosion resistance,has the potential to be applied to the deep tunnel structure.This paper proposed a new composite structure of deep tunnel lined with GFRP pipe,which consisted of three layers of concrete segment,cement paste and GFRP pipe.A new pipe-soil spring element model was proposed for the pipesoil interaction with gaps.Based on the C3D8R solid model and the Combin39 spring model,the finite element numerical analysis of the internal pressure status and external pressure stability of the structure was carried out.Combined with the checking calculation of the theoretical formula,the reliability of the two finite element models was confirmed.A set of numerical analysis methods for the design and optimization of the three-layer structure was established.The results showed that from the internal GFRP pipe to the outer concrete pipe,the pressure decreased from 0.5 to 0.32 MPa,due to the internal pressure was mainly undertaken by the inner GFRP pipe.The allowable buckling pressure of GFRP pipe under the cover of 5 GPa high modulus cement paste was 2.66 MPa.The application of GFRP pipe not only improves the overall performance of the deep tunnel structure but also improves the construction quality and safety.The three-layer structure built in this work is safe and economical.

Topography Structure and Scanning Tunneling Spectrum of Nickel( Ⅱ )-tetraphenylporphyrin Molecules on Au(111)

Scanning tunneling microscopy （STM） and scanning tunneling spectroscopy （STS） were performed on monolayer film of NiTPP supported on Au（111） under ultrahigh vacuum （UHV） conditions. The constant current STM images show remarkable bias dependence. High resolution STM data clearly show the individual NiTPP molecules and allow easy differentiation between NiTPP and CoTPP reported before. Scanning tunneling spectra, as a function of molecule-tip separation, were acquired over a range of tip motion of 0.42 nm. Spectra do not show the variation in band splitting with tip distance. It appears for molecules such as NiTPP that the average potential at the molecule is essentially the same at the same metal substrate. For molecules of the height of NiTPP, the scanning tunneling spectra should give reliable occupied and unoccupied orbital energies over a wide range of tip-molecule distances.

Pressure effect study on the Ⅰ-Ⅴ property of the GaAs-based resonant tunnelling structure by photoluminescence measurement

This paper discusses the I-V property of the GaAs-based resonant tunnelling structure （RTS） under external uniaxial pressure by photoluminescence studies. Compressive pressure parallel to the [110] direction, whose value is determined by Hooke＇s law, is imposed on the sample by a helix micrometer. With the increase of the applied external uniaxial compressive pressure, the blue shift and splitting of the luminescence peaks were observed, which have some influence on the I-V curve of RTS from the point of view of the energy gap, and the splitting became more apparent with applied pressure. Full width at half maximum broadening could also be observed.

Graphene/Rh(111) Structure Studied Using In-Situ Scanning Tunneling Microscopy

Scanning tunnel microscopy （STM） is performed to verify if an Rh ＇nails＇ structure is formed accompanying the graphene growing during chemical vapor deposition. A structure of a graphene island in an Rh vacancy island is used as the start. While the graphene island is removed by oxygenation, the variations of the Rh vacancy island are imaged with an in-situ high-temperature STM. By fitting with our model and calculations, we conclude that the best fit is obtained for 0% Rh, i.e., for the complete absence of nails below graphene on Rh（111）. That is, when graphene is formed on Rh（111）, the substrate remains fiat and does not develop a SUPPorting nail structure.

Wind tunnel simulation of wind loading on a solid structure of revolution

The wind tunnel simulations of wind loading on a solid structure of revolution with one smooth and five rough surfaces were conducted using wind tunnel tests. Timemean and fluctuating pressure distributions on the surface were obtained, and the relationships between the roughness Reynolds number and pressure distributions were analyzed and discussed. The results show that increasing the surface roughness can significantly affect the pressure distribution, and the roughness Reynolds numbers play an important role in the change of flow patterns. The three flow patterns of subcritical, critical and supercritical flows can be classified based on the changing patterns of both the mean and the fluctuating pressure distributions. The present study suggests that the wind tunnel results obtained in the supercritical pattern reflect more closely those of full-scale solid structure of revolution at the designed wind speed.

Rock Pressure on Tunnel with Shallow Depth in Geologically Inclined Bedding Strata

The method to calculate rock pressure to which the lining structure of tunnel with shallow depth is subjected in geologically inclined bedding strata is analyzed and put forward. Both the inclination angle of bedding strata as well as the internal friction angle of bedding plane and its cohesion all exert an influence upon the magnitude of the asymmetric rock pressure applied to tunnel. The feature that rock pressure applied to tunnel structure varies with the incUnation angle of bedding strata is discussed, At last, the safety factor, which is utilized to evaluate the working state of tunnel lining structure, is calculated for both symmetric and asymmetric lining structures. The calculation results elucidate that the asymmetric tunnel structure can be more superior to bear rock pressure in comparison with the symmetric one and should be adopted in engineering as far as possible.

A review of the growth and structures of silicene on Ag(111)

Ag(111) is currently the most often used substrate for growing silicene films. Silicene forms a variety of different phases on the Ag(111) substrate. However, the structures of these phases are still not fully understood so far. In this brief review we summarize the growth condition and resulting silicene phases on Ag(111), and discuss the most plausible structural model and electronic property of individual phases. The existing debates on silicene on Ag(111) system are clarified as mush as possible.

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

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.g.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.

黄土隧道新型组合结构支护效果分析及参数优化研究

黄土隧道在开挖过程中经常发生支护结构破坏或过度变形。依托某黄土隧道,提出一种新型组合结构支护体系(π形拱架),采用理论计算对比了π形拱架与传统工字钢提供的支护反力,结合现场监测和数值模拟分析了不同支护体系下围岩控制效果,优化新型组合结构的构造参数,同时基于正交试验探究了构造参数对围岩支承效果影响显著性大小。结果表明:π形拱架提供的支护反力是型钢钢架的3.14倍,具有强度大、承载力高的优势;建立对比分析模型,较传统支护体系相比,新型支护体系下的拱顶沉降降幅达到53.8%,等效塑性应变减少约64.4%,初期支护最大压应力和拉应力分别减少约35.3%、35.9%;进而建立参数优化模型,通过对围岩竖向位移和塑性区的综合评估,建议拱架壁厚取6 mm,灌浆强度选择C30,翼板长度以200 mm为宜;结合正交试验结果,各因素影响程度由小到大依次为因素B(灌浆强度)<因素A(钢管壁厚)<因素C(翼板长度)。本研究可进一步促进新型拱架在黄土隧道施工支护中的应用。