20 October 2017, Volume 30 Issue 10
    

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  • Synchronous Testing Method for Tensile and Compressive Moduli of Asphalt Mixture Based on Splitting Test
    LU Song-tao, LI Yi-peng, LIU Chao-chao, ZHENG Jian-long
    China Journal of Highway and Transport. 2017, 30(10): 1-7,16.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    In order to truly characterize the ability of tensile and compressive deformation of asphalt mixture, and improve the test efficiency and scientificity of its tensile and compression moduli, the direct tensile and unconfined compressive moduli tests were carried out. Meanwhile, the tensile and compressive moduli in splitting tests were also carried out. The analytical algorithms of the tensile and compressive moduli were derived by integrating the functions of the horizontal and vertical radial strain at the center of the specimen during the splitting test, which based on the Hooke's law in the two-dimensional stress states and the principle of calculus. The quantitative relationship between two kinds of moduli with load magnitude, specimen size, strain gauge length, tensile and compressive resilient strain and Poisson's ratio was obtained. The splitting compressive modulus was close to the uniaxial compressive modulus tested by splitting testing method. Its deviation was within 2%. There existed a small deviation between splitting tensile modulus and direct tensile modulus because of the difference of stress states and stress levels, but the deviation was within the acceptable range. The results show that there is a significant difference between tensile and compressive characteristics of asphalt mixture. The synchronous testing method for tensile and compressive moduli based on splitting test can improve the testing efficiency and scientificity of asphalt mixture. The results can provide scientific parameters for the structural design of asphalt pavement.
  • 2D Model Tests of Soil Arching Evolution in Piled Embankments Using Steel Rod Analogical Soil
    RUI Rui, ZHANG Long, SUN Yi, XU Lu-chang, XIA Yuan-you
    China Journal of Highway and Transport. 2017, 30(10): 8-16.
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    In order to reveal deformation patterns of piled embankments and soil arching evolution during the settlement of the soil, and provide references for parameter selection of piled embankments, a multi-trapdoor test system, in view of interactions between multiple elements in the piled embankments, was developed. The series of trapdoor tests were conducted in consideration of the filling height (H), net spacing (s-a) and width (a) of the piles. Soil arching evolution during the settlement of the soil was observed. Steel rod analogical soil was used as the filling to meet the two-dimension experiment conditions. The effect of the friction on both the front and back plates was eliminated during the test. Particle image velocimetry (PIV) technique was adopted to achieve the whole deformation and several load cells were used to measure the load distribution under the filling. The deformation patterns of the soil arching and the pile-soil stress ratio by dint of different parameters were obtained. The results show that the steel rod analogical soil can accurately simulate the stress-strain behaviors of the soil at the plane. There are two main soil arching evolution patterns of piled embankments, namely, triangular expanding pattern and equal settlement pattern respectively. Compared with the triangular expanding pattern, there is no differential settlement on the embankment surface in the equal settlement pattern. With high soil arching effect, the stress distribution ratio goes on with its trends of a slight decrease. Another tower-shaped evolution pattern can be considered as the transitional pattern between the triangular expanding pattern and the equal settlement pattern. In addition, the application conditions of three evolution models are summarized according to test results. It can be concluded that the relative filling height H/(s-a) of low piled embankments increases through adjusting section sizes of pile-soil, with the purpose of entering the equal settlement pattern.
  • Triaxial Shear Property of Geocell-reinforced Loess
    YAN Chang-gen, GU Liang-jun, YANG Xiao-hua, LU Hao, YUAN Hang
    China Journal of Highway and Transport. 2017, 30(10): 17-24.
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    To investigate shear properties of geocell-reinforced loess, triaxial shear tests were conducted on compacted loess and geocell-reinforced loess with different patterns of reinforcement, by dint of the micro-geocell. The stress-strain curves and shear strength indexes of reinforced loess and compacted loess were obtained. Meanwhile, the stress-strain properties of reinforced loess and compacted loess were investigated. The effect of different reinforcement types was analyzed, and the mechanism of reinforcement with geocell under different layers was discussed. The results show that the stress-strain curves of compacted loess and reinforced loess with geogrid present slight strain-hardening behavior, while the stress-strain curves of geocell-reinforced loess present obvious strong strain-hardening behavior. The reinforcement effect of geocell with 4 layers is optimal, and the reinforcement effect of geocell with 2 layers can act well under the low confining pressure or the large strain. The stress-strain curves of compacted loess and reinforced loess with geogrid are hyperbolas. The fitting effect of such curves by dint of Duncan-Chang model is good. Furthermore, it is better to use power function type to fit the stress-strain curves of reinforced loess with geocell. The friction angle and cohesion of soil increase by the reinforcement with geocell, and the friction angle as well as cohesion of reinforced loess with geocell of 2 layers increases by 38% and 50%, compared with that of compacted loess respectively. Moreover, the friction angle and cohesion of reinforced loess with geocell of 4 layers increase by 63% and 120% respectively, which are higher than that of reinforced loess with geogrid. The reinforcement effect of geocell is better than that of geogrid, and the increase of the layer of geocell can further improve the shear property of loess on account of the existence of “enhanced zone” and “indirect effect zone”. The more the layers are, the larger the thickness of “enhanced zone” and “indirect effect zone” will be. The shear strength of reinforced loess will be improved as well. The results will provide the theoretical basis for the selection of design parameters in the practical engineering.
  • Test Method of Level and Distribution of Hot Mixed Asphalt Surface Texture
    CHEN De, HAN Sen, LING Cheng, PENG Biao, QI Xiang
    China Journal of Highway and Transport. 2017, 30(10): 25-31,38.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To cover the shortage of the existing test methods of hot mixed asphalt (HMA) surface texture, a new test method of level and distribution characteristics of HMA surface texture was proposed based on image analysis techniques and spectral theories. Firstly, 2D image analysis technique was used to identify the HMA surface texture from profile scanning images. Then, macro-texture index (i. e. LTX,0.5-31.5), micro-texture index (i. e. LTX,0.13-0.5), and surface texture distribution indices (i. e. LTX,m) were derived on the basis of spectral theories. Meanwhile, the test analysis software characterizing the level and distribution of 2D HMA surface texture was developed based on MATLAB, Visual Studio, and Install Shield. Finally, indoor comparison tests were carried out between the new method and the traditional test methods of level and distribution of HMA macro-texture and micro-texture. The results show that there are high correlations between results tested by the new and traditional methods of level and distribution of HMA macro-texture and micro-texture. It demonstrates that by dint of this method, the level and distribution characteristics of macro-texture and micro-texture of HMA surface can be accurately evaluated.
  • Test on Low-temperature Performance for High-temperature Pyrolytic Rubber Modified Asphalt（in English）
    DONG Rui-kun, QI Chang-peng, ZHENG Kai-jun, ZHAO Meng-zhen
    China Journal of Highway and Transport. 2017, 30(10): 32-38.
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    In order to investigate the effect of the pyrolysis on the low-temperature performance of modified asphalt, 9 groups of high-temperature pyrolytic rubber modified asphalt were prepared under different processing temperature and processing time respectively, whilst the degree of rubber powder cracking was represented by the solubility of different modified asphalt samples in toluene. The influence rules of processing temperature and processing time on low-temperature performances of modified asphalt were evaluated by 5 ℃ ductility, glass transition temperature Tg obtained by differential scanning calorimetry (DSC) test and S value obtained by bending beam rheometer (BBR) test at-24 ℃. The results show that, when the content of rubber powder reaches 30%, the solubility of the samples processed at 230 ℃ and 250 ℃ tends to gradually increase with the extension of the processing time. When samples are processed at 270 ℃, the solubility of samples increases at first and then decreases with the extension of time, caused by the violent thermal volatilization of light component. With the extension of the processing time, the low-temperature performance of high-temperature pyrolytic rubber modified asphalt prepared at 230 ℃ firstly increases and then decreases. The low-temperature performance of samples prepared at 250 ℃ and 270 ℃ gradually decreases. Compared with processing technologies of traditional rubber powder modified asphalt, the desulfurization and pyrolysis of rubber powder are beneficial to further improve the low-temperature performance of rubber modified asphalt within the definite scope of processing time. Among the 9 groups of high-temperature pyrolytic rubber modified asphalt, the sample prepared at 250 ℃ with stirring for 1h has the best low-temperature performance, followed by the sample prepared under 230 ℃ with stirring for 2 h.
  • Moisture Susceptibility of Warm Mix Asphalt and Binders After Short-term Aging Process
    LI Bo, WANG Yong-ning, LU Zhen-feng, LI Xiao-hui, LI Xiao-min
    China Journal of Highway and Transport. 2017, 30(10): 39-44,52.
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    To explore Evotherm warm mix-asphalt (Evotherm-WMA) and the moisture susceptibility of asphalt mixtures under a short-term aging process, WMA was coordinated in the laboratory at three short-term aging temperatures (112 ℃, 129 ℃ and 146 ℃) and aging time (2 h, 4 h and 8 h). The moisture susceptibility of Evotherm-WMA was measured through immersed Marshall test and freeze-thaw splitting test. In addition, the contact angles of asphalt binder as well as probe liquids extracted from Evotherm-WMA mixtures after a short-term aging were measured by the sessile drop method. And the surface free energy (SFE) of asphalt binders was calculated. The results show that the moisture susceptibility of Evotherm-WMA is poorer than that of hot mix asphalt (HMA) at the initial stage of forming. The moisture susceptibility of the Evotherm-WMA and warm mix binders will be improved or at the same level as the moisture susceptibility of HMA if they are coordinated at certain aging temperature and time. The SFE of asphalt binders extracted from Evotherm-WMA increases with the increase of the coordinated aging time and temperature. Furthermore, there is certain linear correlation between immersed Marshall residual stability of Evotherm-WMA and SFE of asphalt binders.
  • Plastic Analysis of Transverse Effective Width of Top Slabs in Reinforced Concrete Box-girders
    FANG Zhi, CAO Qing, ZHENG Hui
    China Journal of Highway and Transport. 2017, 30(10): 45-52.
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    To investigate the transverse mechanical characteristics of carriageway slabs of the ordinary reinforced concrete box-girder, the plastic-theory-based calculation method of transverse effective width of the traffic deck at the plastic stage was obtained. Two reinforced concrete box-girder models were fabricated and the overall processes of top slabs of concrete box-girder from cracking to failure were monitored and discussed after the mid-span local load. Subsequently, the distribution form of plastic yield-lines and the ultimate resistant-capacity of the top slabs could be obtained at the same time. A plastic analysis model for the top slab in the box-girder was then developed by comparing the failure modes of two slabs. Based on the limit analysis of plastic yield line theory, a formula for predicting the ultimate resistant-capacity and evaluating the plastic transverse effective width of the top slab under the local load was proposed. The applicability of the formula was tested by results. Finally the test results and the theoretical values were compared with values in bridge design specifications at home and abroad. The results indicate that the limit equilibrium method can predict the ultimate resistant-capacity and the plastic transverse effective width of the top slab of reinforced concrete box-girder accurately. The transverse mechanical characteristics of the top slab in reinforced concrete box-girders can be carved by the simplified failure mode at the plastic stage. When the top slab of the box-girder turns to a plastic stage under the local load effects, its transverse effective width is obviously different with that at the elastic stage. That is to say, the effective width based on the plastic analysis is approximately twice as much as width on the basis of the elastic analysis at the ultimate state.
  • Experiment on Seismic Performance of Concrete Columns Reinforced with GFRP Bars（in English）
    DENG Zong-cai, GAO Lei, WANG Xian-yun
    China Journal of Highway and Transport. 2017, 30(10): 53-61.
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    To evaluate the seismic performance of concrete columns reinforced with GFRP bars, the reversed cyclic loading tests for 5 concrete columns reinforced with longitudinal and transverse GFRP (Glass Fiber Reinforced Polymer) bars and 1 concrete column reinforced with longitudinal steel bars and transverse GFRP bars were conducted. The influence of the volumetric ratio of hoop and the level of axial compression on the seismic behavior of concrete columns reinforced with GFRP bars was discussed. The characteristics, including failure patterns, hysteretic curves, the ductility, the dissipated energy, the strength degeneration and the stiffness degeneration were investigated. The two evaluation methods of traditional ductility coefficient and integrated performance index were adopted to evaluate and compare the seismic behaviors of concrete columns reinforced with GFRP bars. The trial value of the flexural capacity were compared with calculated values in CAN/CSA-S806-12, ACI 440.1R-15 and GB 50608—2010 codes. The calculation method of theoretical skeleton curve for FRP reinforced concrete columns was proposed based on the existing experimental researches and experimental results of this paper. The results show that the failure of concrete columns reinforced with GFRP bars is caused by the concrete crushing and the fracture of longitudinal GFRP bars. The failure of hybrid reinforced concrete columns results from the concrete crushing and the yield of longitudinal steel bars. There is no damage of GFRP stirrups of all specimens, and GFRP stirrups can provide effective lateral restraint for the concrete columns during the test. The rheostriction of hysteretic curves of GFRP reinforced concrete columns is evident. The energy dissipation capacity of GFRP reinforced concrete columns is slightly lower than that of hybrid reinforced concrete columns. There are some limits of the evaluation of the seismic performance of GFRP reinforced concrete columns by dint of the traditional ductility coefficient method. The integrated performance index can reflect the high level of bearing capacity and deformability comprehensively. The integrated performance index increases with the increasing volumetric ratio of hoop and the decreasing level of axial compression. The calculation results of flexural capacity of three codes are smaller than trial values, whilst the results of ACI 440.1R-15 code for calculating the flexural strength of GFRP reinforced concrete columns have a rather sufficient safety reserve. The theoretical skeleton curves predicted by the proposed calculation method coincide relatively well with the experimental results.
  • Experiment on Hysteretic Properties of Bridges with Pile-group Foundations Allowing Rocking and Uplift of Pile Cap（in English）
    GUAN Zhong-guo, YANG Bin, DONG Kai, LI Jian-zhong
    China Journal of Highway and Transport. 2017, 30(10): 62-68.
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    To investigate the seismic properties of bridges with pile-group foundations allowing rocking and uplift of the pile cap, typical models with a pile-group foundation allowing rocking and uplift of the pile cap and a pile-group foundation with conventional fixed connections in a large scale were designed and fabricated. The effect of surrounding soil was simulated with container of fine sand, and more considerations were taken for the details in the connections between the pile tops and caps to prevent local damage. The quasi-static test was conducted under an increasing cyclic displacement-controlled loading process. Subsequently, anti-seismic properties of bridges with different pile-group foundations were compared. The results show that only minor damage is incurred to the piles of the new foundation and there is no obvious damage in the connections. The model with the pile foundation allowing rocking and uplift of the pile cap is adopted, and the hysteretic loops take the shape of the flag. It is indicated that the structure primarily experiences nonlinear elastic deformation. Whereas, bridge models with common pile-foundation take the shape of typical spindle-shaped hysteretic loops, showing plastic deformation characteristics. The transition-oriented displacement turns into rotation-oriented displacement, after the uplift of the pile cap. The model with the new foundation mainly accommodates the lateral seismic vibration with the rocking and uplift of the pile cap. Therefore, seismic responses and damage to the piles are reduced. The residual displacement of bridges with pipe foundation is approximately 10% of the displacement of the conventional foundation. The re-centering capacity of pile-group foundation with the uplift is good. It is pointed out that the traditional method on evaluating the stiffness degradation of ductile reinforced structures by using scant stiffness is not suitable for resilient structures. The stiffness coeffients are adopted by reloading under the ultimate states.
  • Experiment on Mechanical Property of RC Beams Strengthened by External Prestressing（in English）
    GAO Rong-xiong, WU Guo-ju, YUE Ying, GAO Ze-yu, YANG Jin-cai
    China Journal of Highway and Transport. 2017, 30(10): 69-80,136.
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    In order to determine the appropriate tension control stress and the height of steel wire to the bottom of RC beam and provide reasonable parameters for external prestress strengthening, seven test beams of contraction scale were designed. The mechanical property, failure mode and ultimate bearing capacity of RC beams strengthened by external prestress respectively under different tension control stress and the height of steel wire to the bottom of RC beam were investigated. The main content of the test included load, deflection, strain, the appearance and development of cracks. The results show that the failure modes of the reinforced beams are similar with those without strengthening, and all the test beams show significant plastic failure characteristics. There are obvious cracks occurrence and development process before the failure for test beams, but the duration is much longer for reinforced beam than that of the beams without strengthening. At the same time, the theoretical bearing capacity of each test beam is calculated according to the bearing capacity theory. The ANSYS software is employed to compare the experimental value and the calculated value. The increasing height of steel wire to the bottom of RC beam is beneficial to the improvement of the bearing capacity. However, when the height increases to a certain degree, the secondary effect is remarkable on account of the increase of the deflection, so the improvement effect of the bearing capacity is significantly weakened. The bigger the tension control stress is, the bigger the cracking load and ultimate load of reinforced beam will be, and the smaller the steel wire stress increment will be. Large tension control stress gives full play to the external prestress strengthening effect. Whereas, when the tension control stress decreases to a certain degree, there is almost no effect on the bearing capacity with any the tension control stress. Compared with the change of tension control stress, the influence of the height of steel wire to the bottom of RC beam on the mechanical property is more significant. Moreover, the external prestress strengthening can significantly improve the bearing capacity of the original beam as well as its ductility, and the plasticity development is more complete in the destruction stage.
  • Shaking Table Test on Structure-soil-pile of PHC in Coastal Soft-soil Area
    FU Cui, HUANG Fu-yun, CHEN Bao-chun, ZHENG Jie-sheng
    China Journal of Highway and Transport. 2017, 30(10): 81-92.
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    In order to give an insight into the seismic responses, pile-soil interactions as well as failure modes of PHC pipe-piles in the coastal soft-soil area, tests on the PHC piles-soil-structure model system under the shaking table were conducted. Different prestress ratios and soil properties were considered to investigate the influence on seismic response and failure mode of PHC pipe pile-soil-structural model system by increasing the peak values and inputing three different earthquake waves. The results indicate that soil saturation has a significant effect on the dynamic parameters and seismic responses of the model system, and the prestress ratio has a certain influence on dynamic properties. The failure modes are different as for the unsaturated soil, the natural frequency of PHC model system slightly decreases under the basic intensity. While for saturated soil, the natural frequency of model system decreases to 50% of the initial frequency with the increase of peak ground acceleration (PGA), which indicates that the model has damage or even failure under the rare intensity. Moreover, the damping ratio and interaction of structure-soil-pile of PHC model will increase. However, the existence of prestress can significantly mitigate the effect of earthquake. In addition, the pore water pressure increases to 1.0 and is liquefied with the increase of PGA and the soil depth, and the duration of liquefaction is far longer than the seismic wave history. The results can provide the basis for the application of PHC pipe-piles in coastal soft-soil area and the implementation of seismic code.
  • Meso-experiment on Vertical Characteristics of Caisson-cushion-pile Composite Foundation（in English）
    ZHU Xiao-jun, FEI Kang, LI Wen-shuai, XU Zhao-yang, GONG Wei-ming
    China Journal of Highway and Transport. 2017, 30(10): 93-99.
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    In order to investigate the vertical bearing characteristics of caisson-cushion-pile composite foundation, a vertical bearing capacity test in view of piled-caisson of deep-water bridge test model was conducted in allusion to three different particle size distributions of gravel cushions. The side friction of pile, pile penetration, gravel flow trend and cushion porosity were developed by applying vertical loads on caisson, embedding strain gauges, soil pressure cells and displacement meter on the pile shaft. Continuous shooting with particle image velocimetry technique was provided during the test. And soil particle displacement field was obtained by dint of the image processing technique. The particle flow code (PFC2D) was employed to analyze the meso-characteristics such as stress transfer mode and porosity of composite foundation. The results show that the gravel particle size distribution has a great influence on the pile penetration. The pile penetration can be reduced effectively by the coarse and graded gravel. The neutral plane of the pile shaft is probably at a depth of 0.4 times pile length and then moved downwards to a depth of 0.7 times pile length. Meanwhile, the porosity of pile head area decreases from 29.2% to 11.2%. The obvious decline indicates that the particles in pile head area are compacted and formed into a core area. And it is consistent with the soil displacement field obtained by the digital image processing. The result of laboratory simulation is consistent with the numerical results from PFC2D. The porosity of the caisson corner edge tends to decrease at first and then increase. The dilatancy characteristics of soil are revealed. The porosity of pile top soil continues to decrease, forming the pile core compaction zone. The research results can provide references for the design of pile-caisson foundation of deep-water bridge.
  • Inverse Analysis of Initial Ground Stress Field of Deep Embedded and Extra Long Highway Tunnel
    DAI Cong, HE Chuan, CHEN Zi-quan, WANG Yao, YANG Wen-bo
    China Journal of Highway and Transport. 2017, 30(10): 100-108.
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    The objective of this paper is to ascertain the initial ground stress field distribution of Lanjiayan extra long and deep embedded highway tunnel along the axis. According to the engineering geological survey report, the 3D geological model of the engineering area was established by ANSYS. Based on the initial ground stress data measured by hydraulic fracturing technique, the main factors influencing the formation of initial ground stress field were determined by the analysis of geological mechanics, and then expressed as the boundary and initial conditions required for the numerical calculation. Under the individual effect of factors, the ground stress values of the measured points were calculated based on the hydraulic fracturing method. The distribution regularity of the initial ground stress field along the axis of the tunnel was obtained by the multiple regression method. According to the regression equation of the initial ground stress field along the axis of the Lanjiayan Tunnel, the stress of the measured points was obtained by dint of stress relief method. The rationality of the inverse regression results was validated after comparing the inverse results with measured values. The results show that the principal stress value presents approximately linear increasing trend with the increase of buried depth, and vertical stress is equal to or slightly higher than gravity stress of overlying rock per unit area. The principal stresses present the regularity of SH >Sh >SV, which means that the initial ground stress field of Lanjiayan Tunnel is dominated by the horizontal tectonic stress. Most of principal stresses are more than 20 MPa, indicating that Lanjiayan Tunnel is a high ground stress field tunnel. Due to the large difference between the maximum horizontal principal stress and the minimum horizontal principal stress, it is found that there is a big shear stress in tunnel level according to the Mohr-Coulomb strength theory, which may lead to the deformation and failure of the surrounding rock. On account of the shear action of the fault, the ground stress changes drastically in the fault area. Compared with the ground stress of region in the front and back of the fault, there is a certain stress relaxation.
  • Modelling of Traffic Flow at Unsignalized Roundabouts Taking Lane-changing Behavior into Account
    GE Ying-en, LI Juan, ZHENG Yuan-hua, XU Chong-feng
    China Journal of Highway and Transport. 2017, 30(10): 109-118.
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    To investigate the impact of frequent lane changes in the waving areas of a roundabout on the efficiency of traffic operations and whether frequent lane changes may cause accidents and traffic jams, considering that the roundabout is similar to the freeway,the vehicles all run on the same side and conflicts only occur on the weaving section, an unsignalized roundabout in this paper is treated as a short ring freeway so that the existing traffic models may be used to analyze the characteristics of traffic flow at roundabouts. The model for traffic flow at unsignalized roundabouts was investigated by introducing a lane-changing intensity variable ε(t,x) on the basis of the kinematic wave theory. Meanwhile, the operational characteristics of traffic flow at roundabouts were analyzed. The traffic flow models at roundabouts were established, taking lane-changing behavior into account. The results show that the proposed model, taking the lane-changing intensity as a variable, can reveal the traffic conditions at roundabouts. The effectiveness of the model is also verified by numerical examples. It is also shown numerically that the frequent lane changes may decrease the capacity of a roundabout. The investigation enriches the existing literature on traffic flow modeling at unsignalized roundabouts.
  • Multi-segment Green Light Optimal Speed Advisory for Hybrid Vehicles
    LUO Yu-gong, HU Shu-mang, ZHANG Shu-wei
    China Journal of Highway and Transport. 2017, 30(10): 119-126.
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    The purpose of this paper is to improve the traffic efficiency of vehicles, and solve the problem of extra energy consumption and forced stop at signalized intersections in the urban area caused by the unreasonable speed control. In allusion to the current situation where the rule-based methods and simple velocity model were mainly applied in related researches to optimize and solve the speed curves, and the speed optimization of vehicles was limited to the traditional internal combustion engine vehicles, neglecting the potential of the energy management of hybrid vehicles in the future, an approach aiming to optimize green light optimal speed advisory (GLOSA) and energy management for hybrid vehicles based on genetic algorithm was proposed. Meanwhile, the scene model of GLOSA and the multi-constrained nonlinear optimization equations in view of varying accelerated model were established. The speed curve and the energy management of the hybrid vehicles were optimized simultaneously by dint of the optimization of acceleration of the vehicle and torque distribution relationship of energy sources. The results show that, at low vehicle speed, the efficiency of the engine calculated by general methods of GLOSA is low. The extra energy consumption is caused by extra travel time. Under the condition that the green light interval is ensured, the total fuel consumption decreases by 5%-29% the optimal energy management of hybrid vehicles is achieved by the proposed method. Meanwhile, the travel time decreases by 20.4% in simulation.
  • Fundamental Diagram Model of Heterogeneous Traffic Flow Mixed with Cooperative Adaptive Cruise Control Vehicles and Adaptive Cruise Control Vehicles（in English）
    QIN Yan-yan, WANG Hao, WANG Wei, WAN Qian
    China Journal of Highway and Transport. 2017, 30(10): 127-136.
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    In allusion to the heterogeneous traffic flow mixed with cooperative adaptive cruise control (CACC) vehicles, adaptive cruise control (ACC) vehicles and manual vehicles, the ACC model and CACC model, validated by PATH laboratory of University of California, Berkeley, were employed as the surrogate models for current commercial ACC vehicles and real CACC vehicles respectively. Meanwhile, the intelligent driver model was used as the manual driven model. An analytical expression was built to reflect the relationship of three types of vehicles in heterogeneous traffic flow. Then, fundamental diagram model of the heterogeneous traffic flow was derived at different CACC penetration rates. The scattered pattern of the fundamental diagram and traffic capacity were also investigated via numerical simulations. Moreover, the sensitivity analyses on desired time-gap of ACC and CACC were carried out respectively. The results show that the error between the analytical expression of heterogeneous traffic flow and the random simulation experiment result is less than 1.5%. Analytical investigation of fundamental diagram can replace the simulation-based investigation of traffic capacity, with the purpose of analyzing traffic capacity of heterogeneous traffic flow for different CACC penetration rates. When the ta is 1.1 s, the traffic flow capacity is gradually improved with the increase of penetration rate (p) of CACC vehicles. If ta is 1.6 s and the penetration rate (p) is below 30%, the capacity of heterogeneous traffic flow is almost the same as that of homogeneous manual vehicles. However, the capacity of heterogeneous traffic flow is less than that of homogeneous manual vehicles if ta is 2.2 s and CACC penetration rate is below 40%. Meanwhile, the smaller the desired time-gap of CACC is, the higher capacity of heterogeneous traffic flow will be. The analytical expression can provide a reference for analytical investigation on other characteristics of heterogeneous traffic flow. Besides, the analytical results of fundamental diagram can provide references for assigning the values of desired time-gap in the upper controller design of ACC and CACC, from the perspective of heterogeneous traffic flow capacity.
  • Freeway Traffic Flow Condition Criterion Method Based on Cusp Catastrophe Theory
    HU Jian-rong, HE Lei
    China Journal of Highway and Transport. 2017, 30(10): 137-144.
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    In order to accurately grasp the condition and the changing law of the freeway traffic flow, and provide the scientific decision-making basis for the driver and the freeway manager, the deficiencies reflected in the traditional traffic flow calculation model were analyzed, and the existing division methods together with models of freeway traffic flow based on the catastrophe theory were improved. The concepts of chaos and catastrophe interval were introduced, whilst the mix rate of the large vehicle was added as the improved model parameters. The criteria of large vehicle chaos flow state, free flow and non free flow state with different mix rates were obtained. Taking the eight-lane expressway standard road as an example, the real-time operation state and changes of traffic flow were simulated by dint of VISSIM, whilst the different traffic flow simulation criterion obtained by calculating. Through the statistical analysis of the measured data of typical freeway sections, the rationality and feasibility of the criterion and method were verified. The results show that the traffic flow changes between free flow and non-free flow condition. During the stage of transformation, there is a transient catastrophe, showing a state of the chaotic flow. The influence of the mix rates of large vehicle on two indicators the driving speed and time occupancy is significant. The corresponding criteria of the chaotic flow, free flow and non-free flow can be obtained as well. Comparing traffic flow state criterion obtained from the simulation with criteria in China and the United States, freeway service has reached the second level or C level and above, and the requirements for the free flow service level are much higher. The method is scientific, convenient, practical and feasible for freeway operation management, the classification of maintenance section and safety evaluation.
  • Engine Torque Requirement Control in Gear Shift Process of DCT Based on Generalized Predictive Control
    BAO Wei, KONG Hui-fang
    China Journal of Highway and Transport. 2017, 30(10): 145-150,158.
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    To solve the problem of the time delay and parameter perturbation of engine torque control system in gear shift process of dual-clutch transmission, the generalized predictive control was put forward for transmission control unit to realize the engine torque requirement control. The characteristic of engine torque control system was analyzed to establish the transfer function of the controlled object. The Pade approximation method was used to further build the discrete model and the CARIMA model of the controlled object. The objective function was created, and the analytical solution of generalized predictive controller was obtained by optimizing the objective function. In order to reduce the computational complexity, the direct generalized predictive control was used to identify parameters of prediction equation to enhance the real-time performance. Finally, according to the data from engine test bench, the generalized predictive controller and the PI controller were designed. The step response, the ramp response, the ability of resisting parameter perturbation and the gear shift performance between generalized predictive control and PI control were compared by simulation tests and hardware-in-loop (HIL) tests. The results show that the torque tracking performance and the ability of resisting parameter perturbation of the generalized predictive control are obviously better than those of PI control. The generalized predictive control can deduce the effect of time delay based on generalized predictive control. It is of great significance for improving the driving quality and the gear shift rapidity of dual-clutch vehicle.
  • Influence of Mineral Particle Size on Mixing Time and Phase Mixing Technology
    LIU Hong-hai, LIU-NIE Yang-zi, HAO Yu-fei, ZHENG Kun-long, SHAO Xiao-feng
    China Journal of Highway and Transport. 2017, 30(10): 151-158.
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    In order to investigate the influence of the adding order of coarse aggregate, fine aggregate, mineral powder and asphalt on the quality and efficiency of asphalt mixture in the process of the mixing, the rolling rule of particles under the action of double horizontal shaft mixer was analyzed by establishing a mixing model. According to the mixing mechanism that asphalt migration occurs on the surface of particles in the process of the rolling, a relational expression between mixing uniformity and particles rolling laps was obtained under the condition that asphalt migration quantity decreased at a certain rate. The rolling relationship between different size particles in the mixing process was calculated through the model of ranging diameter planar circle. Based on the relationship, the technology of phase mixing was put forward. The coarse aggregates, fine aggregates and mineral powder had the same oil film thickness. The double shaft mixer used in laboratory was developed, with the same mixer structure and mixing principle as the mixer used in the practical engineering. The experiment was conducted by dint of AC-16 asphalt mixture. The results show that different particles sizes have different rolling times in the mixing process. The rolling times of the mineral powder are greater than that of fine aggregates, whilst the rolling times of fine aggregates are greater than that of coarse aggregates. Hence, particles with different sizes have different oil film thickness on the surface. The quality of the asphalt mixture and efficiency of mixer can be improved by the phase mixing. Compared with the traditional mixing technology, the amount of asphalt decreases, and the mixing time of the phase mixing can be reduced by 30%.
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