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2024 Volume 41 Issue 4
05 April 2024
  
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  • Study on Performance of Fiber-toughened Waterborne Epoxy Emulsified Asphalt Mixture
    LIU Shu-guang, ZHOU Ming-yu, DAI Yong, LIU Dan, ZHANG Heng-long
    2024, 41(4): 1-11. https://doi.org/10.3969/j.issn.1002-0268.2024.04.001
    Abstract ( ) Download PDF ( ) HTML ( )   Knowledge map   Save
    In order to enhance the toughness of waterborne epoxy emulsified asphalt mixture, 3 different types of fiber materials, namely wood fiber, polyester fiber, and basalt fiber, are utilized. The influencing rules on engineering performance of the waterborne epoxy emulsified asphalt mixture with different dosages (0.2 %, 0.4 %, 0.6 %) is investigated. Marshall stability test, uniaxial compression creep test, low-temperature splitting test, freeze-thaw splitting test, dynamic modulus test and indirect tensile fatigue test are conducted on 9 groups of fiber-modified waterborne epoxy emulsified asphalt mixtures. The evaluation indicator results are obtained including Marshall stability, creep deformation, failure tensile strain, freeze-thaw splitting tensile strength ratio, dynamic modulus, and fatigue life. Comparative analysis is carried out with the performance of blank samples. The result shows that the optimal emulsion content of mixture increases with the addition of fibers. The bond strength among aggregates is enhanced significantly, and the resistance to water damage is improved effectively. Simultaneously, fiber modification has a significant influence on the toughness and expansibility of waterborne epoxy emulsified asphalt mixture. The maximum failure tensile strain in the low-temperature splitting test for the fiber-toughened mixture increases by 33.6 % at most. Based on the effect of fibers on improving the performance of waterborne epoxy emulsified asphalt mixtures, basalt fiber exhibits the best performance, followed by polyester fiber, and wood fiber ranking third. Considering both engineering performance and cost-effectiveness, recommended dosages for wood fiber, polyester fiber and basalt fiber are determined as 0.2 %, 0.2 %, and 0.4 % respectively. It is worth noting that a high dosage of fibers may lead to poor dispersion in the mixture and to form mechanical weak points. Therefore, caution should be exercised in selecting fiber dosages.
  • Spatio-temporal Distribution of Rutting Deformation of Cold Recycled Test Road with Asphalt Pavement
    XU Guang-ji, SAI Zhi-yi, LIU Jiu-wei, MA Tao, ZHANG Jing-lin
    2024, 41(4): 12-21,41. https://doi.org/10.3969/j.issn.1002-0268.2024.04.002
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    In order to reveal the mechanical behavior of cold recycled asphalt mixture in the structure and provide a reference for structural design in road maintenance, relying on the cold recycled asphalt pavement structure and field sensor monitoring data from an expressway test road in Shandong province, the dynamic response characteristics of cold recycled asphalt pavement under traffic load are analyzed. Based on the measured temperature field data, a viscoelastic finite element simulation model is constructed to analyze the rutting distribution of cold recycled asphalt pavement structures. The result shows that for the cold recycled asphalt mixture layer of the test road structure, the driving speed has a power function relationship with the duration of the internal strain response of structure. At the speed of 60-80 km/h, the mechanical response frequency inside the structural layer is close to 10 Hz. In pavement design, the dynamic modulus of the cold recycled mixture at 20 ℃ and 10 Hz can be adopted as the structural modulus. The distribution of hourly rutting volume in a day is mainly related to traffic volume in the cold recycled asphalt test road structure. The distribution of monthly rutting volume in a year is mainly related to temperature, the rutting accumulation within a year mainly occurs from May to October, and the rutting amount in winter can be almost negligible. In order to avoid excessive rutting predictions due to increased layer thickness, the thickness of asphalt layer needs to be limited when calculating the equivalent temperature for permanent deformation of the asphalt mixture layer. In addition, compared with the change of dynamic modulus at high temperature, controlling the plastic deformation development rate of the asphalt mixture in the upper and middle surface at about 40-45 ℃ shows a more significant effect in reducing the accumulation of pavement permanent deformation.
  • Optimization Design of PCB/WCF Modified Asphalt Mixture Based on Response Surface Methodology
    GAN You-wei, LI Chuang-min, DENG Qin-hao, GAN Xin-zhong
    2024, 41(4): 22-30. https://doi.org/10.3969/j.issn.1002-0268.2024.04.003
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    In order to improve the water stability of waste tire pyrolysis carbon black (PCB) modified asphalt mixture, by using the wool fiber of waste chicken feather (WCF), which is beneficial to the improvement of water stability of asphalt mixture, PCB/WCF modified asphalt mixture with gradation AC-13 is prepared. First, the microstructure and surface chemical element distribution of PCB and WCF are analyzed by using a laser particle size analyzer, scanning electron microscope and energy dispersive spectrometer. Subsequently, an experimental plan based on the response surface methodology (RSM) is designed to investigate the effects of PCB content, WCF content and asphalt-aggregate ratio on the porosity, Marshall stability and freeze-thaw split tensile strength ratio of asphalt mixture AC-13. Finally, the impact of 3 independent variables and their interactions on the asphalt mixture's porosity, Marshall stability and freeze-thaw split tensile strength ratio is studied by using analysis of variance (ANOVA), and a predictive model for the performance of PCB/WCF modified asphalt mixture AC-13 is established. The result shows that. The particle size distribution of PCB is concentrated in the range of 197-358 nm, and the surface ash content reduces the compatibility between PCB and asphalt. The feathers on both sides of the WCF shaft are distributed fan-shaped with the main chemical elements of carbon, nitrogen, oxygen and sulfur. The optimal parameters obtained from the optimization model for PCB/WCF modified asphalt mixture AC-13 are PCB content of 0.52 %, WCF content of 0.36 % and asphalt-aggregate ratio of 5.5 %. The corresponding predicted values are porosity of 3.85 %, Marshall stability of 11.79 kN and freeze-thaw split tensile strength ratio of 84.56 %. The validation experiments for AC-13 PCB/WCF modified asphalt mixture prepared based on the optimal parameters result in porosity of 3.69 %, Marshall stability of 11.6 kN and freeze-thaw split tensile strength ratio of 84.9 %, all within a 95 % confidence interval, indicating that the model has good predictive capability. The predicted values and experimental verification values of the optimized design for PCB/WCF modified asphalt mixture AC-13 meet the performance requirements for modified asphalt mixtures in China.
  • Analysis on Mechanism and Influencing Factor of Asphalt Pavement Arch Expansion Disease in Desert Area
    LIN Yu-kun, SONG Ling, LIU Jie, YAN Xiao-liang, ZHU Shi-yu
    2024, 41(4): 31-41. https://doi.org/10.3969/j.issn.1002-0268.2024.04.004
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    Due to the problem of asphalt pavement arch expansion disease in S21 Altay-Urumqi expressway in Altay desert area, the mechanism and influencing factors are analyzed. Through the field investigation and test, the causes of asphalt pavement arch expansion disease are analyzed. Based on Kirchhoff's thin plate theory and finite integral transformation method theory, the calculation formula of critical stress of base arch expansion is derived. The mechanical mechanism of asphalt pavement arch expansion disease is analyzed, and the critical stress value of base arch expansion is determined. The finite element model of the road is established, and the influence of the factors(e.g. base construction temperature, expansion coefficient, resilient modulus and maximum temperature of the pavement surface)on the maximum longitudinal stress of the base and the maximum arch height of the pavement surface are analyzed. Based on the critical stress value of base arch expansion, the corresponding recommendations are given. According to the study, the asphalt pavement arch expansion disease in S21 Altay-Urumqi expressway is the result of arch damage of the cement stabilized gravel base under excessive temperature stress. Considering the actual road conditions, When the maximum longitudinal stress is greater than the base arch expansion critical stress value, the base will occur arch instability damage. The base construction temperature, expansion coefficient, resilient modulus, and maximum temperature of the road surface are all sensitive factors for the maximum longitudinal stress of the base, while the resilient modulus of base has no significant effect on the maximum arch height of pavement. It is suggested that the base expansion coefficient is within 2.8×10-5 ℃-1, and the base resilient modulus is 1 400-2 200 MPa.
  • Mechanical Property and Microscopic Mechanism of Nano-SiO2-lime Stabilized Loess Subgrade
    JIA Liang, ZHANG Wei-wei, FENG Xiang, LIAN Yong, GUO Jian
    2024, 41(4): 42-50. https://doi.org/10.3969/j.issn.1002-0268.2024.04.005
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    The stabilization method of loess has always been a study focus of subgrade engineering in loess area. Nano-SiO2 is an inorganic flocculent silicide characterized by the small size effect, surface energy effect and pozzolanic effect, thus attracting wide attention in soil stabilization. In order to explore the promotion effect and improvement mechanism of nano-SiO2 on the mechanical properties of lime stabilized loess, 3 types of specimens are designed including 3 % lime stabilized loess specimens, 3 % lime+nano-SiO2 comprehensively stabilized loess specimens,and 8 % lime stabilized loess specimens. Based on the 3 types of specimens, the unconfined compressive strength test, resilience modulus test, California bearing ratio CBR test and SEM test are conducted to study the effects of curing agent content and curing time on the mechanical properties and microstructure of loess subgrade. The result shows that the introduction of nano-SiO2 sharply enhances the unconfined compressive strength, resilience modulus, and CBR of loess. 0.2 % nano-SiO2 +3 % lime stabilized loess achieves the same mechanical properties as 8 % lime stabilized loess. With the increase of nano-SiO2 content and curing time, the strength of loess subgrade increases gradually. The relationships of unconfined compressive strength, CBR and resilience modulus are established with regression fitting of the test data. SEM test shows that the addition of nano-SiO2 improves the aggregation form of soil particles, and fills the voids of soil particles thereby enhancing the mechanical properties of loess subgrade. Comprehensively considering the confined compressive strength, resilience modulus, CBR and economy, the mixture proportion of comprehensively stabilized loess is recommended as 3 % lime +0.2 % nano-SiO2. The nano-SiO2-lime stabilized loess technique provides an environmentally friendly and lower-cost stabilization approach for loess subgrade.
  • Influence of Wind Load on Vehicle-bridge Coupling Vibration and Riding Comfort
    WANG Shao-qin, MA Shi-jie, GUO Ming-hao, LIN Jing-shu, QIAO Hong
    2024, 41(4): 51-64. https://doi.org/10.3969/j.issn.1002-0268.2024.04.006
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    In order to ensure the safety of the long-span bridge structure,and the stability and comfort of vehicle running on bridge, a coupling vibration analysis model for wind-vehicle-bridge is established. The roughness of the bridge surface with different grades is simulated by using the trigonometric series method to study the excitation source of the vehicle. The vertical and lateral wind load is generated by using the fast spectral analysis method. A dual-axle, four-wheel, 13-degree-freedom car model is established. The Jiujiang Yangtze River bridge with a span of (180+216+180) m is selected as the engineering background. A finite element model for the bridge is established for natural frequency and vibration mode calculation. The mode superposition method is used to establish the differential equations of vehicle-bridge coupled vibration balance, and Newmark-β integral iteration is adopted to solve the time varying equations. The specification ISO2631-1997 is used to calculate the vibration response of the vehicle body, and the total weighted acceleration root-mean-square of vehicle is calculated. The acceleration time history is performed with spectrum analysis to evaluate the driving comfort. The dynamic responses and riding comfort are analyzed when vehicles passing the bridge under different wind loads, driving speeds and bridge roughness, and the dynamic loads of wind and vehicles on the bridge are calculated as well. The result shows that the dynamic responses of the vehicles increase with the increase of wind speed, the deterioration of bridge surface roughness and the raise of vehicle speed. The riding comfort will deteriorate accordingly.The increase of the wind velocity reduces the maximum vertical displacements of the bridge, while the vertical acceleration and lateral vibrations increase significantly. Long-span bridges are sensitive to wind and vehicle dynamic loading, therefore, sufficient attention should be paid on the design and operation stages of bridges to ensure the safety of both bridge structure and running vehicles.
  • Numerical Simulation on Wind Characteristics at Y-shaped Valley Bridge Site
    ZHU Pei-zhang, HU Bo, LIU Zhi
    2024, 41(4): 65-72. https://doi.org/10.3969/j.issn.1002-0268.2024.04.007
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    The wind field characteristics in complex mountainous areas are different from those in plain areas. The wind field is very complex and lacks a unified pattern, which has a significant impact on the structural vibration of large-span bridges. In order to study the influence of complex mountainous terrain on the wind field characteristics at bridge site, taking a cable-stayed bridge located at the intersection of several valleys as the engineering background. Based on ALOS digital elevation terrain model, the wind field characteristics at bridge site with different wind directions are calculated by CFD numerical simulation method.The influence of the main valleys at bridge site, and the local terrain at bridge site on the average wind speed, wind attack angle, wind deflection angle,and the vertical wind profile in the middle of bridge span along main beam is analyzed.The relationship between the average wind speed and the wind attack angle in the transverse direction of bridge is studied, and the relationship between the incoming flow conditions with wind speed amplification effect and the topographic characteristics of the bridge site is discussed qualitatively.The result shows that the wind characteristics at the Y-shaped valley bridge site are different from those at the general mountain bridge sites. When the incoming flow is along several relatively straight valleys, the average wind speed at bridge site is larger, and the wind speed at other wind directions is smaller. The bend of the valley results in the backflow and diversion of the incoming flow along the valley. In this case, the wind attack angle at the bridge site is large, the variation range of wind deflection angle along the main beam is relatively large, the horizontal wind speed is small, and there is no wind speed canyon amplification effect. The local topography of the valley at the intersection of bridge site has a great influence on the vertical wind profile in the middle of bridge span. The study result provides a basis for the determination of the design wind speed of bridge, and can provide guidance for the qualitative judgment of the wind characteristics at bridge site of Y-shaped valley.
  • Study on Dynamic Characteristics of Continuous Beam Bridge Based on Vehicle-bridge Coupling Vibration
    WANG Jun-xia, ZUO Xin-dai, SHEN Lin, LI Hua-teng, LI Zhou
    2024, 41(4): 73-79. https://doi.org/10.3969/j.issn.1002-0268.2024.04.008
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    In order to obtain the dynamic characteristics of continuous beam bridge under driving load, a 24-DOF typical four-axle trailer dynamic model is established based on the principle of virtual work, and the dynamic characteristics model of three-span continuous beam bridge is established by using the modal superposition method. The mechanical and displacement coupling relationship between wheel and bridge deck is established by using the relevant theories of modal synthesis method. The dynamic coupling analysis model of four-axle trailer and continuous beam bridge is established, and the time-varying matrix equation of vehicle-bridge coupling is established by step iteration method. Taking a three-span continuous beam bridge as an example, the sensitivity analysis for vehicle-bridge coupling dynamic characteristics is carried out, and the influence of vehicle running speed, deck unsmoothness and vehicle load on the dynamic response at the key position of bridge is analyzed. The result shows that with the increase of traffic speed, the vertical displacement time-history response curve of the bridge increases as a whole. The vertical displacement amplitude of the side span increases relatively little (3.40 %), while the vertical displacement amplitude of the middle span decreases first and then increases, with the maximum increase of 7.10 %. With the deterioration of bridge deck condition, the vertical displacement response of the side span and mid-span section of bridge increases relatively greatly, which are 38.60 % and 54.95 % respectively, which are the main sensitive parameters of the bridge dynamic response. When the vehicle load is relatively small (from no-load to 40 % full load), the dynamic response of the bridge displacement is more sensitive, but with the increase of the growth rate of vehicle load, the sensitivity of bridge dynamic response to the vehicle load gradually decreases. The relevant study results can also provide reference for the dynamic response analysis and study for other types of bridges or structures.
  • An Analysis on Collapse Margin for Highway CFST Arch Bridge Considering Uncertainty
    WEN Qian-xin, ZHANG Tong, LI Dong, XIAN Li-na
    2024, 41(4): 80-89. https://doi.org/10.3969/j.issn.1002-0268.2024.04.009
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    In order to study the collapse margin capacity and earthquake loss of bridge structure based on the influence of uncertainty, an analysis method is proposed to calculate the bridge collapse margin ratio (CMR) based on the member damage margin ratio (DMR), and this method is used to evaluate the loss of the structure in the event of earthquake. Taking a highway CFST arch bridge as an example, firstly, the uncertainty of the model information is fully considered, and the Latin hypercube sampling is used to combine the model information parameters randomly. The OpenSees program is used to establish the elastic-plastic dynamic analysis model for arch bridge, and the nonlinear time-history analysis is carried out. Then the probabilistic seismic demand model of components is established by using probabilistic seismic demand analysis (PSDA) method. The vulnerability curve of components under continuous earthquake is determined, the vulnerability curve of the bridge is finally determined by analyzing the damage of different main load-bearing members in the event of earthquake, and the relationships among DMR, CMR, earthquake loss and uncertainty is explored. By comparing the 2 working conditions with different uncertainty, the result shows that (1) uncertainty has an important impact on CMR, DMR and earthquake loss assessment; (2) under the action of a given ground motion intensity, the DMR decreases with the uncertainty increase, resulting in an increase in the seismic loss of the component; (3) under the same earthquake, the components with smaller DMR are more likely to be destroyed than those with larger DMR; (4) under the influence of uncertainty, the change trend is consistent with that of DMR, because the CMR of bridge structure is obtained by DMR. Through the evaluation of DMR of members, fully considering the influence of uncertainty in the evaluation process is helpful to more accurately understand the collapse margin capacity of the structure and the loss in the event of earthquake.
  • Numerical Analysis on RC Slab Culvert Rehabilitated with Corrugated Steel Semi-circular Arch
    LI Bai-jian, FU Wen-qiang, FU Xin-sha, HE Yu-ting
    2024, 41(4): 90-98. https://doi.org/10.3969/j.issn.1002-0268.2024.04.010
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    In order to probe into the mechanical properties of the reinforced concrete (RC) slab culvert rehabilitated with corrugated steel semi-circular arch, the method for mutual verification between laboratory test and numerical analysis is adopted. On the basis of proposing and verifying the numerical analysis method for the RC slab culvert rehabilitated with corrugated steel semi-circular arch based on elasto-plastic equivalence of grout, the major factors affecting the bearing capacity of the reinforcement system are analyzed. The result shows that (1) The system transformation of reinforced concrete culvert takes place after reinforcement, the slabs change from flexural members before reinforcement to composite members with arch effect after reinforcement, and the failure mode shifts from the flexural failure before reinforcement to the shear failure after reinforcement. The ultimate bearing capacity of the reinforcement system depends on the shear capacity of the RC slab, the shear bearing capacity of the filled concrete and the bending capacity of the corrugated steel. The bending capacity of the RC slab, which has limited effect on the reinforcement system, mainly plays its shear bearing capacity. (2) The ultimate carrying capacity of the reinforcement system is 13.23 times higher than the theoretical ultimate carrying capacity of the slab before the reinforcement, presenting obvious reinforcement effect. (3) The maximum displacement and relative error of the reinforcement system are 16.27 % and 0.191 7 % respectively,and it is favorable to adopt the elasto-plastic equivalent method for the filled concrete to establish numerical model to simulate the bearing capacity and deformation of the reinforcement system in the ultimate state. (4) Meanwhile, the slab thickness, filled concrete strength and corrugated steel waveform are the key parameters affecting the reinforcement system bearing capacity, among which the filled concrete strength, followed by the slab thickness, has the greatest influence on the bearing capacity of the reinforcement system, and the selection of the corrugated steel waveform needs to balance the bending capacity of the corrugated steel and the shear bearing capacity of the filled concrete.
  • Study on Most Unfavorable Pier Position of Local Scour Around Parallel Bridges with Unequal Spans
    CHEN Xiao, XU Jie-liang, CHEN Qi-gang, LIU Ang, HUANG Ran
    2024, 41(4): 99-109. https://doi.org/10.3969/j.issn.1002-0268.2024.04.011
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    In order to quickly locate the most unfavorable pier position of parallel bridges, the generalized model test combined with numerical simulation method is used for studying the influence of span combination and arrangement of two-column abutment parallel bridges on the most unfavorable pier position. The result shows that the most unfavorable pier position of local scour around parallel bridges is mainly distributed near the river center along the river width and concentrates in the first row of piers of each two bridges along the flow direction. The most unfavorable pier position of local scour depends on the relative layout of two bridges' arches. When the downstream pier is within the tail flow area of upstream pier, the most unfavorable pier position is at the upstream bridge. Conversely, when the downstream pier is in the accelerated flow area, the position occurs at the downstream bridge. In practical engineering, the geometric variable θ can be used as a key variable in determining the distribution of the most unfavorable scour positions of parallel bridges, and it also reflects the extent of the influence of wake zone of parallel bridge piers, thus indicating the method of determining the location of the most unfavorable pier position. After locating the distribution of the most unfavorable piers along the direction of flow and the width of river, the angle between the first row of two bridge piers and the incoming flow direction could be expressed. When the angle is less than 14°, the most unfavorable pier is located at the first row of piers of upstream bridge, conversely, it is located at the first row of piers of downstream bridge. The study result can provide reference and basis for the design, assessment and protection against flooding of parallel bridges with unequal spans.
  • Calculation Method for Stable Ultimate Bearing Capacity of Irregular Space-shaped Bridge Pylon
    WANG Huan, KANG Ling, MU Ting-min, CHEN Ming
    2024, 41(4): 110-119. https://doi.org/10.3969/j.issn.1002-0268.2024.04.012
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    The geometric configuration of irregular space-shaped bridge pylon (IS-SBP) is complex, which has the characteristics of irregular cross sections and non-ideal boundaries. It is difficult to obtain the stable ultimate bearing capacity (SUBC) by using the existing methods, and the safety of structure cannot be accurately perceived so that the material cost increases. Whereas the development of this kind of bridge pylon is rapid and with large numbers, the stability issues are prominent with the trend of towering structures, high strengthening materials and thin-walled components, and there is an urgent need to carry out study on the SUBC. The essence of the stability problem of bridge pylons is analyzed. By focusing on nonlinear stability safety factors and systematically considering the effects of component slenderness ratio, material nonlinearity, geometry nonlinearity and initial defects, the internal mapping relationship between stability safety factors and stability reduction factors is established, and the analysis method for the SUBC of IS-SBP is proposed. Then, the feasibility and accuracy of the proposed method are verified by comparing the SUBC results with the value from specifications by using the examples of typical ideal compression pylons, e.g. rectangular and circular reinforced concrete compression pylons, pure-steel box compression pylons,and concrete-filled steel box pylons. Finally, based on a typical IS-SBP cable-stayed bridge, a refined nonlinear finite element simulation strategy is constructed to obtain its SUBC. The result shows that the elastic stability safety factor of the structure is 18.56, the nonlinear stability safety factor is 4.125, and the stability reduction factor is 0.899. The SUBC is greatly reduced after considering the dual nonlinearity and initial defects, and the nonlinear stability safety factor is only 0.22 times of the elastic stability safety factor. For irregular space-shaped strut-pylon structure, the influence of nonlinearity on the SUBC of structure should be considered in design.
  • Key Construction Technology for Steel-concrete Composite Beam Bridge Decking Prepared with PF-UHPC
    YANG Yuan-hai, WANG Bin, HUANG Qing-wei
    2024, 41(4): 120-131. https://doi.org/10.3969/j.issn.1002-0268.2024.04.013
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    In order to investigate the influence of different technical indicators on the performance of UHPC bridge decking in steel-concrete composite beams, to improve the preparation technology of premix for UHPC (PF-UHPC), and to produce steel-concrete composite beams with stable performance and meeting construction requirements, the influences of different technical indicators on the working performance and mechanical properties of PF-UHPC are compared and analyzed through experiments. The optimal technical indicators are determined, and a set of key technologies is developed for the construction of prefabricated and cast-in-place steel-concrete composite beam bridge decking with PF-UHPC. The result shows that the strength and working performance of the PF-UHPC base mix proportion meet the requirements, and increasing 0.3 % dosage of water reducer can significantly improve the material's working performance without affecting its mechanical properties. When using a large mixer with a mixing time of 8 min, the best performance of the mixture is achieved. The setting time of materials is greatly influenced by indoor and outdoor environmental factors. The feeding sequence of steel fibers has a relatively small influence on the working performance and mechanical properties of the material, but the mixture with added steel fibers has a significant deviation in the uniformity of steel fibers. The flexural strength of the specimen is influenced by the orientation of steel fibers, which mainly depends on the direction of fabric. The greater the angle between the fabric direction and the flow direction of UHPC, the lower the flexural strength of the test decking. The vibration frequency has a significant influence on the flexural strength of UHPC, but has a smaller influence on the deviation of compressive strength and steel fiber content, and the 80 Hz vibration frequency is the most favorable. The hydration heat temperature of UHPC after wet curing is basically between 40 ℃ and 50 ℃, and the initial internal temperature increases with the increase of plate thickness. During the steam curing process, the temperature rise in the center of the UHPC plate is slower than that of the outside, and the temperature difference between the inside and outside is larger. The constant temperature inside the steam curing shed should be controlled above 90 ℃, and the natural cooling time should be appropriately extended. The bottom of a 25 cm thick decking should be kept at a constant temperature above 70 ℃ for 30 h, and its strength should meet the design requirements.
  • Research Status of Green Tunnel Construction and Maintenance Technology
    GAO Xiao-jing, CUI Dan-yi, LI Lei, XU Chong-bang
    2024, 41(4): 132-145. https://doi.org/10.3969/j.issn.1002-0268.2024.04.014
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    With the steady advancement of the national strategy ‘dual-carbon', the concept of green development has become more deeply rooted in people's minds. As an important infrastructure for enhancing the efficiency of transportation and the level of service, green tunnel is receiving more attention. The national policy requirements related to green transportation and the research of green tunnel technology are analyzed. The connotation and extension of green tunnels are analyzed from the perspectives of green concept, ecological environmental protection, intensive and economical use of resources, energy saving, carbon reduction and emission reduction, comfort and convenience, intelligence and efficiency, etc. The definition of green tunnels is given. Based on the technology characteristics of green tunnels during construction and maintenance periods, the relevant research and development status are sorted out and summarized such as prefabricated assembly technology, ground-source heat pump technology, low-carbon concrete material invention, environmentally friendly tunnel routing, green design of tunnel entrances and gates, construction wastewater treatment technology, reuse of cave slag, invention of low resilient shotcrete material, energy-saving technology for lighting, energy-saving technology for ventilation, active and passive noise reduction measures, intelligent inspection system for operating tunnels, and automated detection of diseases and accurate identification technology. Considering the shortcomings and development trend of tunnel greening technology comprehensively, the future development of green tunnels is elaborated from the aspects of standardized tunnel construction complete sets of technology, engineering application of low-carbon structural materials, whole life cycle tunnel information modeling technology, evaluation of negative ecological effect and ecological environmental protection and restoration, resourceful use of waste and harmless discharge, intelligent control machine of electromechanical system using green auxiliary technology, intelligent equipment,etc. The study can provide certain reference for the green transformation of tunnels.
  • Study on Information Perception of Visual Illusion Speed Control Marking in Approach Section of Expressway Tunnel
    LIANG Bo, QIN Yang, ZHANG Hong-jie, LIU Tao, WEN Sen
    2024, 41(4): 146-156. https://doi.org/10.3969/j.issn.1002-0268.2024.04.015
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    Due to the black hole effect at the entrance of expressway tunnel and the difference in the speed limit between the inside and outside of tunnel, the entrance of the expressway tunnel has become a road section with high accident rate. In order to improve the safety and comfort of driving at the entrance of expressway tunnel, the visual illusion speed control marking is often set up in the approach section of tunnel to give drivers visual impact, which plays a role in reminding drivers to slow down safely. UC-win/Road is used to establish a simulation model, and the simulation test is carried out through the indoor simulation driving platform. A driver's visual information perception is measured by eye tracker, and the physical indicator speed reduction rate, maximum deceleration value and physiological indicator pupil diameter change rate are selected as evaluation indicators. The weighted RSR comprehensive evaluation method is used to evaluate the deceleration effect of speed-increasing visual illusion speed control marking (transverse-shaped and fishbone-shaped) and lane-compression visual illusion speed control marking (comb and inclined comb) with different flash rates on left and right lanes. The result shows that the 4 visual illusion speed control markings can affect drivers' ability to perceive information, and the influence degree is:fishbone-shaped > transverse-shaped > positive comb teeth-shaped > oblique comb teeth-shaped. The deceleration effect of visual illusion speed control markings with the same type and different flash rates is different. With the same flash rate, the deceleration effect of the speed increased visual illusion speed control marking is better than that of the lane-compression visual illusion speed control marking. In order to meet the requirements of driving comfort, transverse-shaped visual illusion speed control marking with flash rate of 8 Hz is recommended for fast lane, and fishbone-shaped visual illusion speed control marking with flash rate of 8 Hz is recommended for slow lane.
  • Influence of Width-length Ratio of Foundation Pit on Deformation of Adjacent Existing Tunnel Under Dewatering Condition
    HE Xiao-hui, XIA Xue-qin, LUO Cheng, DING Hai-bin, KONG Yue-yue
    2024, 41(4): 157-166. https://doi.org/10.3969/j.issn.1002-0268.2024.04.016
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    The influence of foundation pit dewatering construction on the deformation of adjacent existing tunnel has been studied by scholars, but the influence of width-length ratio of foundation pit on the maximum vertical displacement of tunnel under dewatering condition is still blank. In order to explore the influence of the width-length ratio of foundation pit on the deformation of adjacent tunnel during foundation pit dewatering, firstly,the stress and deformation rule of the adjacent tunnel is studied with the model test when the width of foundation pit and the depth of dewatering are changed. Then the influence of the width-length ratio of foundation pit is further analyzed with the numerical software. Finally, the vertical displacement of tunnel is normalized, and the influence of the width-length ratio of foundation pit on deformation of the adjacent existing tunnel under the influence of different dewatering depths is analyzed. The result shows that through the model test, it can be found that the causes obvious dewatering funnel outside the pit. With the increase of foundation pit width and depth, the amount of water increase gradually. The water level in the pit continues to decrease, and the vertical displacement and bending moment of the existing tunnel change significantly. The tunnel outside pit presents a deformation like ‘flat horizontal duck egg'. Through numerical analysis, it can be found that when the width-to-length ratio of foundation pit is small, the width-to-length ratio and the dewatering depth should be considered comprehensively, while when the width-to-length ratio of the foundation pit is large, the phenomenon of over-drop should be particularly avoided. In addition, through normalization, it is found that the displacement curves at each dewatering depth approximately satisfy the same function relationship. When the width-to-length ratio of foundation pit is less than 0.4, the larger the width of foundation pit, the larger the displacement of tunnel. When the width-to-length ratio of foundation pit is greater than 0.5, the vertical displacement of tunnel will not increase with the increase of foundation pit width, but the range of tunnel displacement will increase by 4 to 5 times.
  • Pedestrian Evacuation under Fire in Three-lane Highway Tunnel with Large Traffic Flow
    WANG An-min, PENG Wei-yuan, HE Jia-yin, GUO Jia-cheng, YAN Tao
    2024, 41(4): 167-175. https://doi.org/10.3969/j.issn.1002-0268.2024.04.017
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    In order to study the influence of tunnel transverse channel spacing and traffic flow size on pedestrian evacuation, based on the three-lane Yanglin highway tunnel with large traffic flow in Kunming, Yunnan, the fire burning and the evacuation model with the large traffic flow in the three-lane tunnel is established. The available safety egress time (ASET) is calculated by FDS, and the vertical and horizontal spreading rule of fire smoke in the three-lane tunnel is simulated. The necessary ASET is calculated by Pathfinder, and the 2 times are compared and analyzed. The result shows that (1) the distance from the fire source is an important factor affecting the safe evacuation time available for pedestrian, the ASET within 50 m from the fire source is less than 470 s, and this area is relatively dangerous; (2) the necessary evacuation time at 100 m from the fire source is 230 s; (3) away from the fire source of about 50-300 m, the ASET is longer in the range of 470-600 s; (4) when farther than 300 m, the ASET tends to infinity, indicating that this area is relatively safe to escape; (5) the required safe egress time (RSET) increases gradually with the increase of the distance from the fire source; (6) the farthest distance, from the cross passage with fire to the next one without fire, takes 627 s; (7) the RSET at each measuring point is longer than the ASET, indicating that the design parameters of the cross passage of Yanglin tunnel meet the requirements of pedestrian evacuation under the worst fire condition. It can be considered that the safety evacuation design of pedestrian under fire conditions in Yanglin tunnel is reasonable, and provides a useful reference for the fire safety design of similar traffic tunnels.
  • An Adaptive Vehicle Segmentation Algorithm Based on Symmetric Frame Differential Constraint
    WU Hong-tao, MENG Ying, LEI Ling-yu
    2024, 41(4): 176-185. https://doi.org/10.3969/j.issn.1002-0268.2024.04.018
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    In order to achieve accurate detection of vehicle targets in traffic videos and improve the prevention effect of traffic accidents, the vehicle segmentation algorithm for traffic video with the constraint of symmetrical frame difference is proposed. Firstly, the idea of symmetric difference is used to differentiate 3 adjacent consecutive images twice, and a background selection and update method with mixed Gaussian model based on adaptive distribution constraint is proposed to initially extract and update the background of high-definition video. Jump degree and stability in the image are used to determine whether a pixel belongs to a false target point. The background selection update mechanism is proposed to detect foreground targets, and the adaptive distribution number mixed Gaussian model algorithm is used to improve the computational efficiency of the Gaussian mixture model for achieving accurate separation of foreground targets. Secondly, for the resulting image, a shadow detection and removal algorithm based on vehicle edge correction is proposed, and vehicle segmentation detection features are enhanced under the complex background. Then, the moving vehicle target in the result image is segmented and detected by self-adaptive threshold. Besides inter class variance, the cohesion of video foreground target class is considered as a criterion for threshold selection. The adaptive threshold selection algorithm with maximum variance ratio is adopted, and the stopped vehicle is segmented by background updating and filtering. Finally, the experimental result shows that the proposed method can segment vehicle targets with different traffic scenes completely and accurately. In addition, the proposed method effectively improve the detection accuracy of vehicle targets with different situations in traffic.
  • Recognition and Evaluation on Expressway Traffic Accident Information Using Multimodal Data
    CHEN Jiao-na, TAO Wei-jun, JIN Yin-li
    2024, 41(4): 186-193,213. https://doi.org/10.3969/j.issn.1002-0268.2024.04.019
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    In order to extract emergency response information from natural language descriptions of traffic accidents, a named entity recognition method is proposed based on pre-trained models and BiLSTM-CRF. The multimodal traffic accident data on expressways from June 2021 to August 2022 in Shaanxi province are analyzed as data sources. Firstly, 3 deep learning models are compared on entity recognition effect and training time. Secondly, the traffic accident corpus from official microblog is obtained to test the robustness. Moreover, according to the dimensions of consistency and richness, the evaluation indicators are constructed to enable quantitative assessment of traffic accident content for text data and structured data. Finally, the traffic accident information recognition is carried out by using the test dataset. The result shows that the weighted F1 values of BERT-BiLSTM-CRF on both test dataset and out-of-bag dataset are 97.029 4 % and 69.155 5 %respectively, which have the best comprehensive performance in terms of model accuracy, training efficiency, and robustness. It is verified that there is a positive correlation between the number of emergency disposal entities and the duration of accident. The correlation coefficients of disposal agency, disposal equipment, un-disposal, disposal-ing and disposal effect are 0.309, 0.151, 0.137, 0.220 and 0.178 respectively. The content consistency of weather, road loss, traffic diversion, accident type and casualty are 7.06 %, 45.79 %, 1.59 %, 67.65 % and 47.59 % respectively. The proportion of emergency response is 36 %, and the variability is 1.305. It is proved that text data contain rich emergency disposal information, however, the content consistency of text data and structured data for the same traffic accident should be improved. The study result can provide reference for improving the quality and effectiveness of traffic accident information.
  • A Bottleneck Model Considering Indifference-zone of Traveler's Arrival Time
    REN Zi-rong, CHENG Lin, DU Ming-yang, SONG Mao-can, ZHANG Chen-hao
    2024, 41(4): 194-203. https://doi.org/10.3969/j.issn.1002-0268.2024.04.020
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    In order to remedy the defects of Vickrey bottleneck model and its extension research, which ignore the characteristics of travelers' bounded rationality, so as to reduce the error of bottleneck model and alleviate urban traffic congestion, commuters' bounded rationality time understanding is combined with bottleneck model. Based on the assumption that traveler's perception of arrival time has indifference zone, a bottleneck model considering the asymmetry of traveler's arrival time indifference-zone is established, and the departure rate and equilibrium solution analysis are carried out. The indicators of equilibrium departure rate, total cost, equilibrium cost, maximum queue length and total queue cost are derived in detail by numerical analysis. Furthermore, the new model is extended to the cases of indifference band symmetry, early arrival time indifference band and late arrival time indifference band, and the departure rate analysis and equilibrium solution analysis are performed as well. By comparing with the basic bottleneck model, the properties of traveler's departure time decision and equilibrium solution are analyzed in the bottleneck model considering indifference-zone asymmetry and 3 expansion cases. Finally, the conclusions are verified by numerical examples. The result shows that (1) the total cost, equilibrium cost, total early arrival cost, total late arrival cost and maximum queue length all become smaller under the condition of arrival time indifference-zone, and the decreasing amplitude is related to the sum of the widths of arrival time indifference-zone; (2) the commuter departure rate function changes from 2 stages to 3 stages; (3) the commuting peak may be advanced or delayed, and the specific time is determined by the unit early arrival time cost, unit late arrival time cost, width of indifference-zone and other parameters; (4) the use of flexible working system can homogenize peak traffic flow, thereby reducing congestion.
  • Long Term Prediction on Urban Traffic Flow Based on Multi-source Spatio-temporal Graph Convolutional Neural Network Model
    LEI Bin, LI Jia-lu, ZHANG Peng, LI Wei, CHEN Chen
    2024, 41(4): 204-213. https://doi.org/10.3969/j.issn.1002-0268.2024.04.021
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    Traffic flow prediction is an important part of intelligent transport system. Accurate, timely and effective prediction information are of great significance for urban traffic control and guidance. However, due to the fact that urban road network traffic flow is affected by various external factors such as land use properties and weather changes, the traffic flow prediction faces enormous challenges. In order to predict the traffic flow of urban road networks effectively, multi-source spatio-temporal graph convolutional neural network model is proposed. The external factors affecting urban traffic flow are divided into static and dynamic categories. A clear and structured classification basis to understand the various external factors affecting traffic flow is provided. Then, the static factors are coded into multiple graphs, specifically distance matrix, functional similarity matrix,and connectivity matrix. The three-channel input spatio-temporal correlation modeling module is composed of multiple graphs. The graph convolution network is used to model the spatial correlation of traffic flow, learning node features,and adjacency information. The door control cycle single element is used to model the temporal correlation of traffic flow for capturing dynamic changes and periodic patterns of traffic flow data. Finally, the fusion layer is used to fuse the multi-channel output with dynamic factors as the final predicted output. In order to verify the model effectiveness, SZ-TAXI dataset is used for comparing with 7 benchmark models. The result shows that the multi-source spatio-temporal graph convolutional neural network model integrated multiple external factors achieves optimal performance than benchmark model in the evaluation indicators of MAE and RMSE. The ablation experiment shows that the multi-source method for handling static factors and the method for integrating dynamic factors effectively improve the long-term prediction performance of urban road network traffic flow.
  • Dynamic Pricing and Production Optimization for Two-stage Sales of Fresh Agricultural Product
    LIANG Ao-nan, WANG Shu-yun
    2024, 41(4): 214-222. https://doi.org/10.3969/j.issn.1002-0268.2024.04.022
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    Taking live broadacast pre-sale and production optimization of fresh agricultural products as the research object, considering the comprehensive impact of fresh agricultural products' freshness, price,and marketing efforts on consumer demand, the two-stage demand functions of pre-sale static pricing and conventional sales dynamic pricing are constructed respectively. With profit maximization as the objective function, the optimal control theory and Pontryagin maximum value principle are applied. The two-stage pricing and production optimization are planned and solved in order to provide support for the static pricing of live broadcast pre-sale of fresh agricultural products,the dynamic pricing of regular sales,and the operation management of production optimization. The example analysis shows that the conventional price is higher than the pre-sale price, and the optimal profit of conventional sales is much higher than the pre-sale profit. The sensitivity analysis of the example shows that the live broadcast pre-sale pricing and regular sales pricing increase with the increase of sensitivity coefficient of consumer freshness in the pre-sale stage, which leads to a substantial increase in profits of two stages. The sales price of the two stages increases with the increase of the pre-sale time, but the total profit of the two stages decreases with the increase of the pre-sale time. When the selling time is same, the conventional price always increases with the increase of unit inventory cost. However, when the selling time changes and the unit inventory cost is less than the threshold value of 0.03, the conventional price decreases with the extension of selling time. When the unit inventory cost is not less than the threshold value of 0.03, the conventional price increases with the extension of selling time. With the increase of freshness deterioration rate, the freshness of fresh agricultural products decreases slowly in the early stage and faster in the late stage. The management inspiration is that the fresh agricultural product cooperatives should reasonably set the pre-sale time according to the product sales cycle, and use the pre-sale to seize the market, and improve brand awareness. The cooperatives should pay attention to the freshness sensitivity coefficient of consumers in real time, and adjust the level of marketing efforts and pricing strategies accordingly. For agricultural products with a high rate of freshness deterioration, the cooperatives may consider appropriate preservation measures to slow down the rate of freshness decline.