20 September 2017, Volume 30 Issue 9
    

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  • Evaluation of Anti-sliding Durability of Asphalt Mixture Based on Pressure Film Technology
    WANG Duan-yi, WANG Gang, LI Zhi, SHAO Shen-shen, SUN Yang-yong
    China Journal of Highway and Transport. 2017, 30(9): 1-9.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    In order to evaluate the anti-sliding durability of the asphalt mixture, an accelerated loading testing machine of kneading was invented by dint of the pressure film measuring technology. The pressure film technology was adopted to conduct a static load pressure film test on different rut boards of asphalt pavement after kneading for 0, 2, 4, 6 and 8 hours respectively. The anti-sliding durability of asphalt mixture was evaluated based on new indicators proposed by dint of pressure film measuring technology as well as the data analysis. Two films of 0.2-0.6 MPa and 0.5-2.5 MPa were used to investigate the active area and stress concentration effect of the rut board and tire after different kneading time, whilst the 3D effect graph of stress concentration was also rebuilt by means of data analyses. The results show that different kneading time leads to different effective area between the tire and the pavement. The effective area increases with the increase of kneading time. There is an obviously rising trend during the process of 8 hours of kneading. The concentration of stress between the tire and the pavement varies with different kneading time. There is an apparently decreasing tend during the process of 8 hours of kneading. The pressure film measuring technology can well reflect the true contact condition between the tire and road surface and the attenuation process of road stress concentration. With the same raw materials, the anti-sliding performance and durability of GAC-13 road are better than the ones of AC-13 road. Two indexes, that is, stress concentration distribution rate and attenuation rate of anti-sliding performance are proposed to represent anti-sliding durability of the asphalt mixture. There is the good correlation of anti-sliding durability, structure depth and BPN. It is valid and reliable to evaluate the anti-sliding durability. The research provides a reference for the further design of asphalt mixture with anti-sliding performance by dint of the above-mentioned indexes.
  • Field Prediction Method and Experiment on Creep Response of Asphalt Pavement
    PAN Qin-xue, ZHENG Jian-long, YANG Bo, ZHA Xu-dong, LIU Hong-fu
    China Journal of Highway and Transport. 2017, 30(9): 10-17.
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    In order to reveal the viscoelastic characteristic of asphalt pavement structure in service and provide a reference for the asphalt pavement design based on the viscoelastic constitutive theory, static load creep tests on asphalt pavement were conducted under different temperatures and axle loads by means of temperature and strain sensors on the asphalt surface. The tests were designed by dint of the three-dimensional linear viscoelastic constitutive theory,in allusion to the situation that existing strain tests of asphalt pavement were on the basis of the elastic constitutive hypothesis. The applicability of existing constitutive models used to represent the viscoelasticity of asphalt layers were discriminated based on change laws of measured strain. The influence of external factors (including temperature, deviatoric stress, etc.) on viscoelastic parameters of asphalt layers was analyzed. Hence, the prediction model on strain of asphalt layer changing with external factors was established. The results show that the viscoelastic properties presented by the measured creep duration curves are consistent with Burgers model. The determination coefficient is more than 0.98. Four parameters of Burgers model G1, G2, η1 and η2 decrease with the increasing temperature, and increase with the increase of deviatoric strain. The parameters have the good linear relationship with deviatoric strain and the exponential function relationship with temperature. Meanwhile, the correlation coefficients are more than 0.84. Amongst the parameters, viscous parameters η1 and η2 were obviously affected by temperature and deviatoric strain. The strain calculated by dint of prediction model coincides with the measured strain in the same working condition. The relative error of their values is less than 10%, which shows that asphalt surface strain prediction method based on three-dimensional viscoelastic constitutive relationship is reasonable and feasible.
  • Behavior and Micro-mechanism of Cement-based Modified Compaction Soil Composed of Steel Slag and Metakaolin
    WU Zi-long, ZHU Xiang-yang, DENG Yong-feng, LIU Hua-shan, ZHA Fu-sheng
    China Journal of Highway and Transport. 2017, 30(9): 18-26.
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    On the basis of three issues, namely, the recycling of industrial waste slag, the application of high-performance geopolymer in modified compaction soil and performance improvement of cement-based modified compaction soil, a series of tests in laboratory were conducted on cement-based modified compaction soil with additive steel slag and metakaolin. The macro behavior of cement-based modified compaction soil was discussed in detail from compaction properties, compressive strength as well as splitting tensile strength. Thereafter, the microstructure tests (including SEM, XRD, TGA and MIP) were adopted to clarify the internal mechanism (including hydration product, microstructure and pore size distribution) to provide the theoretical basis for the recycling of waste and performance improvement of cement-based modified compaction soil. The results of macrostructure tests show that the steel slag can improve the compaction characteristics and mechanical strength of the cement-based modified soil, whilst the metakaolin can significantly improve the above performance. It is worth noting that with the additive of metakaolin, the strength increases and then decreases, and the optimal ratio between metakaolin and cement is in the range of 1/3 to 1/2. Furthermore, the splitting tensile strength is proportional to unconfined compressive strength, with the ratio of 0.83. The results of microstructure tests show that the additive of steel slag and metakaolin cannot change the types of hydration products of the cement-based modified compaction soil, but change the parcel formation and the number of hydration gelling. Hence, the microstructure and porosity distribution are altered. In a word, the steel slag and metakaolin improve the behavior of cement-based modified compaction soil with different quality.
  • Erosion Morphology, Damage Mechanism and Prediction of Concrete Pavement Under Sandstorm Environment
    HAO Yun-hong, LIU Yan-chen, GUO Jian, HE Xiao-yan, FENG Yu-jiang, JIANG Nan
    China Journal of Highway and Transport. 2017, 30(9): 27-33,50.
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    Based on the characteristics of sandstorm environment in the northwest of China, a simulated sandstorm experiment was conducted to investigate the erosion behavior of cement mortar and the erosive wear damage mechanism of concrete pavement under the environment of sandstorm. The erosion rate of cement mortar was used to evaluate the degree of erosive wear of cement mortar. The change law of erosion rates of cement mortar was analyzed from the different erosion velocity and angle. The surface microtopography of cement mortar was observed by scanning electron microscope (SEM) and laser scanning confocal microscopy (LSCM), whilst the damage mechanism of cement mortar was investigated. The similarity theory was used to analyze the corresponding transformation relationship between actual erosion time and erosion time simulated in laboratory. The results show that when the erosion angle is constant, the erosion rate increases with the increase of the velocity. When the erosion angle is in the range of 30° to 90°, there is an obvious increase in the erosion rate with the constant sand flow rate. The erosion rate increases in proportion, and when erosion angle is 90°, the erosion rate reaches the peak. The erosion angle is the most important factor which influences the erosion behavior. The deformation of the cement mortar with low angle erosion is in the form of plastic deformation, mainly caused by the cutting action of sand along horizontal direction. However, the deformation of the cement mortar with high angle erosion is in the form of brittle damage. The erosion pits on the surface is mainly caused by the vertical impact of sand. The greater the sand flow rate in the experiment is, the longer the erosive wear time in actual conditions can be. The results provide the basis for the research on the wear and damage of cement concrete pavement in the sandstorm environment.
  • Numerical Analysis on Bearing and Deformation Behavior of Horizontally Loaded Batter Piles
    CAO Wei-ping, FAN Wen-fu
    China Journal of Highway and Transport. 2017, 30(9): 34-43.
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    To investigate the bearing and deformation behavior of horizontally loaded batter piles, the finite element method (FEM) was utilized to simulate the performance of batter piles under the horizontal load, whilst horizontal batter piles were compared with vertical piles. The influence of pile shaft inclined angle and vertical load on the horizontal displacement, bending moment and shear force of batter pile was investigated. With the exploration of the extrusion and shear interaction between the pile and the surrounding soil, factors influencing the effective length of batter pile under horizontal load were discussed. The results show that the horizontal bearing capacity of the vertical pile is less than that of the positive batter pile, but greater than that of the negative batter pile. The horizontal displacement, bending moment and shear force of batter piles are significantly influenced by the pile shaft inclined angle. The horizontal displacement of the vertical piles is greater than that of the positive batter piles, but less than that of the negative batter piles. The bigger the shaft inclined angle is, the greater the difference of the horizontal displacement between the vertical and the batter piles can be. The bending moment of the batter piles, whether positive or negative, is less than that of the vertical piles. And the bigger the inclined angles are, the smaller the bending moment is for the positive batter piles, but the greater the bending moment is for the negative batter piles. Compared with vertical counterparts, both two types of batter pile have smaller shear force than vertical piles, and the shear force of positive batter piles is smaller than that of the negative batter piles. It is apparent that the vertical load acting on pile head has different impact on the horizontal bearing capacity of the positive and the negative batter piles. The application of the vertical load can increase the horizontal bearing capacity of the positive batter piles while decrease the capacity of the negative batter piles. The extrusion between the batter pile and the surrounding soils is much stronger than the mutual shearing. There exists an effective length for horizontally loaded batter piles with the same effective length for the positive and negative batter piles regardless of the magnitude of the shaft inclined angles. It is obvious that the effective length is notably affected by the module ratio of the upper soil surrounding the pile but with less influence of the module ratio variation of the bottom of soil.
  • Research on Soil-water Characteristic Curve of Unsaturated Mixed-soil in Western Sichuan
    CUI Kai, LIN Wei-kang
    China Journal of Highway and Transport. 2017, 30(9): 44-50.
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    The geological structure and climate conditions are complicated in the western area of Sichuan, the deformation or landslide damage of the non-saturated mixed-soil roadbed were often caused by the traffic load and rainfall infiltration. Engineering properties of unsaturated soil were closely related to the matrix suction. In order to investigate the effect of mineral composition of unsaturated mixed-soils and dry density on the soil-water characteristic curve in western Sichuan, soil-water characteristic curves of three typical unsaturated mixed-soils in western Sichuan were measured by filter paper method and pressure plate method under different dry densities. The macro phenomenon was analyzed to explore the influence mechanism of the characteristics of the mixed-soil by dint of microscopic characteristics. The results show that mineral composition has a significant effect on soil-water characteristic curves. The higher the content of hydrophilic minerals in the soil is, the greater the matrix suction will be, and the smoother the curve will be. On the contrary, when there is high quartz content and low clay content in the soil, the corresponding matrix suction is usually low. Under the same matrix condition, the larger the dry density is, the larger the soil water content can be. The effect of dry density on the soil-water characteristic curve increases with the decreasing water content. Van Genuchten (VG) model is used for fitting the mixed-soil water characteristic curve, and the fitting parameters are related to the particle size distribution and unsaturated degree. Hence, the fitting curves are in line with the experimental curves. The results can provide the theoretical basis for the analysis of the structure of saturated mixed-soil in Western Sichuan.
  • Experiment on Blast-resistance Performance of Reinforced Concrete Piers（in English）
    ZONG Zhou-hong, TANG Biao, GAO Chao, LIU Lu, LI Ming-hong, YUAN Su-jing
    China Journal of Highway and Transport. 2017, 30(9): 51-60.
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    To investigate dynamic response characteristics, damage modes and failure mechanism of reinforced concrete (RC) piers under the blast loading, the near-field explosion test and contact explosion test were conducted on 11 RC pier specimens by controlling the scaled distance of explosion in the form of increasing the amount of the explosive and reducing the distance between the explosive and the pier. Parameters, including the section form, slenderness ratio, concrete type, stirrup type and axial compressive ratio were taken into consideration in the design of specimens. Based on the Hopkinson scaling law, a formula revealing the relationship between overpressure and scaled distance was obtained by fitting. The results show that the section strain may decrease and cracks development of concrete can be inhibited, in the case of non-contract explosion, by increasing the section area and employing special materials such as steel fiber reinforced concrete, square section and spiral stirrup. Hence, blast-resistance performance of RC piers can be enhanced. In the case of contact explosion, serious local damage and punching failure are more likely to occur at the contact position of the explosive. Moreover, a large number of transverse cracks generate on the surface of piers. In addition, it should be noted that there is a negative effect of the square section and axial loading on the blast-resistant performance of RC piers under contact explosion. The results provide references for setting blast-resistance specifications of bridges.
  • Design and Model Test on Split-combined Caisson Anchorage Foundation of Suspension Bridge（in English）
    MU Bao-gang, ZHU Zhi-rong, GONG Wei-ming, ZHAO Xue-liang
    China Journal of Highway and Transport. 2017, 30(9): 61-69.
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    In order to increase the ease of sinking for traditional caisson, and remain good bearing capacity of traditional caisson anchorage foundation, a new kind of split-combined caisson anchorage foundation, which is separate in sinking period and combined in service period, was designed and verified by groups of indoor model tests. Based on the characteristics of capacity and principle of equal sinking volume, the steel model caisson with the length of 400 mm, the width of 200 mm, and the height of 800 mm was chosen to carry out the horizontal loading model test in sand with same density to determinate the reasonable space between two separated caissons. The differences of bearing capacity and displacement between traditional and split-combined caisson were comparatively analyzed, whilst the characteristics of earth pressure distribution and displacement tendency were tested and analyzed under short and long-term horizontal loading. The results show that split-combined caisson is a possible alternative to traditional large open caisson anchorage, and horizontal bearing capacity of split-combined caisson is better than that of traditional one. The horizontal load in the portion of 65% of the front caisson is much larger than that of the back one in model test. Under the long-term horizontal load, the deformation of the caisson is different from that of the ordinary caisson in the failure stage. The horizontal sliding displacement ratio of the split caisson is about 60%. The time of reaching stability of the caisson deformation is about twice the soil pressure. The final displacement of the soil in front of the caisson is about 3 times longer than the initial displacement. The degree of participation decreases with the increasing distance from the caisson. The experimental results provide the basis for practical engineering application of the split-combined caisson.
  • Transversal Mechanical Behavior of Steel-UHPC Light-weighted Composite Bridge Deck System
    SHAO Xu-dong, ZHENG Han, HUANG Xi-jun, PENG Bo
    China Journal of Highway and Transport. 2017, 30(9): 70-77,85.
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    In order to investigate the transversal mechanical behavior and the composition of transversal stresses of a light-weighted composite bridge deck system with orthotropic steel deck and ultra high performance concrete (UHPC) layer under local wheel loads, static loading test of the full-scale model and finite element numerical simulation were conducted. The static loading tests were carried out on the same full-scale model under the simply supported conditions in the transverse direction and transverse cantilever conditions, whilst the stress state of the composite deck was simulated by changing the boundary condition. The finite element analysis results were compared with experimental values to verify the correctness of the finite element model. The transverse force composition of the composite bridge deck under local wheel load was obtained in view of the finite element analysis. The results show that the transversal stress of the composite deck under vehicle loads has an obvious local effect and the transverse stress is mainly confined to the two U-ribs near the load-bearing area. The effect of the additional bending moment of the bridge deck caused by the bend of the transverse rib is slight.Meanwhile, the primary stress of the composite deck concentrates on the third structural system, and bending moment of the corresponding section accounts for 75% of the total.The proportion of the third structural system stress decreases rapidly out of this region and the second structural system stress becomes the major force.The composite bridge deck is still in elastic stage when the load increases to 300 kN. The UHPC layer is still not cracked, when the maximum transversal stress on top of UHPC layer is 11.9 MPa. Hence, the stress meets the design requirement.
  • Experiment on Dynamic Response of Piers Subjected to Rolling Stone Impacting
    LUO Zheng, WANG Yin-hui
    China Journal of Highway and Transport. 2017, 30(9): 78-85.
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    To accurately estimate the dynamic response of bridge structures in mountain area where there were collisions caused by rolling stones, the impact test of rectangular piers extensively used in western mountain of China in different sizes, namely, 20 cm×20 cm, 30 cm×30 cm and 40 cm×40 cm was carried out. The pendulum dropping of different height, namely 45°, 90° and 135° was used, whilst the impact response and failure mechanism of piers were analyzed from perspectives of the dynamic damage extension, impact force and dynamic response at the top of piers. The time-history curves of impact force were compared with the specification (JTG D10-2016) for design of highway subgrades and formulas of equivalent impact force proposed by Japan Highway Public Corporation. The results show that the global and local damage may occur under the effect of impact loads. The local damage in the form of shear crack occurs in the impact area while the global damage in the form of bend crack occurs at the bottom of the pier. The increase of global stiffness of the pier has little effect on the local damage of concrete in the impact area. The displacement of the top of the pier decreases and the peak of impact force increases. With the increase of the height of the gravity pendulum, the initial kinetic energy of the impact, the displacement of the top of the pier and the peak value of the impact force increase. The impact force calculated by dint of the design formula in Specifications for Design of Highway Subgrades is small and there exists the insecurity of design. Whereas, in terms of the formula proposed by Japan Highway Public Corporation, the analysis result is identical with the peak of impact measured in the test. Hence, the formula proposed by Japan Highway Public Corporation should be adopted in projects.
  • Curved Bar Connection Configuration Used for Wet Joints of Deck of Composite Girder（in English）
    SU Qing-tian, HU Yi-ming, TIAN Le, ZENG Ming-gen
    China Journal of Highway and Transport. 2017, 30(9): 86-92.
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    According to the mechanical characteristics of wet joints of prefabricated decks in composite girder bridge and the existing applications of bar connections at the wet joint, a new type of curved bar connection with the characteristics of simple structure and convenient construction was proposed. To examine its basic mechanical behavior, the tensile experiment of full-scale model was carried out under the axial force, whilst the mechanical behaviors between the straight bar connection type and U-shaped bar connection type was compared by experiments. The cracking load, ultimate load and crack distribution of three types of wet joints were analyzed. The results show that the failure mode of the wet joint of curved bar connection is the same as that of straight bar type and U-shaped bar type. All types of connections first cracked at the junction interface of the dry and wet concrete, and the corresponding cracking loads of the three types of wet joints were almost the same. With the increase of the load, the old cracks width increases, whilst new cracks appear in succession. Finally, the bars around the interface of dry-wet concrete yield, and the three types of wet joints reach to the limit state of tension. The strain of the bars in the middle part of the joint is half the bars at the interface, and the ultimate bearing capacity of the wet joint of curved bar connection is slightly higher than that of others. In theory, the distribution of the bars of wet joints connected with curved bars is more uniform in thickness direction. The bearing capacity can be improved to some extent. It is verified that the wet joint of curved bar connection is better than the other two types in controlling concrete crack width and the bearing capacity of the structure. So it is feasible and reliable to apply wet joints with curved bars connection to the project.
  • Lateral Stability Calculation Theory and Verification of Single-column Girder Bridge
    WANG Bing-jian, ZHAO Hang, ZHANG Hao, PENG Wei-bing, LU Cheng-yuan
    China Journal of Highway and Transport. 2017, 30(9): 93-100.
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    In allusion to a hidden peril in the lateral stability of single-column girder bridge, five kinds of possible failure modes were proposed by the investigation on the collapsed wreckage of single-column girder bridges. Based on the typical failure mode, all the anti-torsion bearing failure (void) was considered as the criterion of judging the overturn. A limited anti-torsion support was used to simulate the beneficial effects of the size on the overturn. The overturning process was regarded as the superposition of the deformation rotation and rigid body rotation. Moreover, the effect of the reaction redistribution caused by large rotation on anti-overturn of the bridge was also considered. Furthermore, the space force system was established to judge whether the overturn occurred in two modes (with or without considering bearing size) based on energy method and variation principle. Taking Chunhui Bridge, the ramp bridge in Honghu section of the third ring road in Harbin, the ramp bridge in Yuegan Expressway and the ramp bridge in Jinjin Expressway as examples, the proposed theory was verified and the further analysis was carried out on influence factors. The results show that compared with the normative calculation which regards the bridge overturn as the rigid body rotation, the proposed computing method takes the effect of the deformation rotation, rigid body rotation and the large rotation of girder on bridge overturn into consideration. The calculated critical overturning loads of four bridges are close to measured values. Hence, the proposed computing method can be used to predict the anti-overturning capacity of the single-column girder bridge.
  • Key Design Issues of Circular Diaphragm Wall and Axisymmetric Finite Element Method
    HE Wei, FAN Zi-yi, LUO Chao-yun, CUI Jian-feng, ZHANG Jian-ren
    China Journal of Highway and Transport. 2017, 30(9): 101-108.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To perfect the computing theory of the circular diaphragm wall, key issues of the existing specifications were discussed from the perspective of mechanical concepts, hoop stress calculation, soil-structure interactions, and the hoop stiffness reduction coefficients. Moreover, basic differential equations of the circular diaphragm wall connected to springs on its both sides were deduced by dint of the thin-shell theory, and a nonlinear soil spring model was proposed to take the ultimate displacement into account. The distributed springs were used to model inner ring beams. The incremental method was adopted to simulate excavation process, and the finite element program was drawn up. Furthermore, the hoop stiffness reduction coefficient was investigated by the testing method. A formula was then established to estimate its value based on factors such as the joint stiffness and width, the diameter of a circular diaphragm wall, and the mean panel length. Subsequently, the program was calculated and analyzed, taken deep excavation program of Yangluo Bridge as an example. The results show that the value is in the range of 0.467-0.679 under the typical condition. Calculated values are basically identical with the measured ones. Compared with the traditional methods, the new method proposed in this paper can be deployed to analyze hoop stress of the supporting structure together with the development of earth pressure on both sides of the diaphragm wall. The axisymmetric finite element method (FEM) is adaptable to the calculation of parameters, and parameters can be obtained easily. The proposed method provides a comprehensive analysis on the engineering design.
  • Optimal Control Model of Multiple Bus Signal Priority Requests for Isolated Intersection Based on Speed Guidance
    ZHANG Peng, LI Wen-quan, CHANG Yu-lin, XIE Jun-ping
    China Journal of Highway and Transport. 2017, 30(9): 109-115.
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    In order to improve the efficiency of passing the isolated intersection where there were high traffic saturation and multiple priority requests for buses, a mix integer linear program (MILP) model integrated with intersection signal timing and bus speed was proposed. With the consideration that the bus speed could be conducted and adjusted, the bus speed adjustment and intersection signal phase duration optimization were regarded as variables, and the aim was to minimize the bus delay and stop times. The constraints were the cycle length and phase saturation. In the model, 0-1 variable was adopted to express bus stop times and whether a bus can pass through in the arrival cycle.The results show that, with high traffic saturation of the intersection, the maximum adjustment of bus arrival time is ±8 seconds. Compared with the original signal timing scheme, the bus delay per person decreases by 14.35 s (27.71%), whilst bus stop times decrease by 1 (14.29%) based on "the bus speed optimization model". The bus delay per person decreases by 12.39 s (23.93%) and bus stop times decreases by 1 (14.29%) based on "the signal timing optimization model". The bus delay per person decreases by 40.68 s (78.56%) and bus stop times decreases by 3 (42.86%) based on the new model presented in this paper, which have gone beyond the sum of individual signal optimization and speed guidance. Furthermore, even if the signal timing and bus speed guidance are taken into consideration, the bus delay per person decreases by 17.29 s (33.39%) and bus stop times decreases by 1(14.29%)with the FCFS (first come first serve). Ideal bus signal priority effect can be achieved by increasing the adjustment quantity of the bus speed with high traffic saturation of intersection and limited signal timing adjustment.
  • Emission Factors of CO and NOx of Urban Tunnel with Concave Structure Based on Measurement Method
    CHEN Chao, HU Qin-qiang, DEGN Yi-wen, LI Qiong, LI Yan
    China Journal of Highway and Transport. 2017, 30(9): 116-124.
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    To characterize the emission of vehicles in urban tunnels, the field measurement was conducted on CO and NOx concentration together with relevant parameters in cross-river tunnel of East Yan'an Road, cross-river tunnel of Xiangyin Road in Shanghai and Xiang River Tunnel of Yingpan Road in Changsha from 2012 to 2013, based on measurement method of the tunnel. The data reflecting in-use fleet average emission factors of CO and NOx in urban tunnels of China were deduced. The results show that as for one-way twin-bore tunnels with concave structure, the effect of natural ventilation caused by external factors is limited. The ventilation caused by movement of vehicles has a positive effect on pollutant dispersion and dilution. In-use fleet average emission factors of CO and NOx are (0.754±0.561)-(6.050±5.940), and (0.121±0.022)-(0.818±0.755) g·km-1·vehicle-1 respectively when gradient is from -6% to 6%. The findings in accordance with results calculated by Permanent International Association of Road Congresses (PIARC) in 2012 are significantly less than designed values in the current specifications of highway tunnels. The results can provide references for the engineering design of ventilation in urban tunnel of China.
  • Research on Efficiency of Toll Road Dual-track Operation System Based on Three Stage DEA and Tobit Regression Model（in English）
    XU Hai-cheng, WANG Yi, JIA Rui-ning
    China Journal of Highway and Transport. 2017, 30(9): 125-132.
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    Aiming at the choice of the dual-track operation model of toll road industry, an empirical research was conducted to explore the operational efficiency differences between the government loan-repayment road and the operating road. On the basis of the pooled cross-section data from 2014 to 2015, three stage DEA was adopted to measure the operational efficiency of toll roads of 29 provinces in China, whilst Tobit regression model was adopted to analyze the effect of government loan-repayment road on overall operation efficiency. In this way, the differences of the efficiency between government loan-repayment road and operating road were compared. The results indicate that the overall operation efficiency of toll road industry under the dual-track system is just 0.717, far less than that of the railroad transport enterprises and highway listed companies.The differences between the first stage DEA results and third stage DEA results are not obvious, that is to say, operation inefficiency mainly results from the inner management system rather than exogenous environmental factors. The increasing proportion of the government loan-repayment road has a significantly negative impact on the operation efficiency of the whole industry. In other words, the operation efficiency of the government loan-repayment road is lower than that of the operating road. The key point of the reform in the short term is to realize system innovation by redefining the function and role of competent authority of the industry. What's more, it is necessary to improve the franchise system and enforce the PPP model to ensure the ordering transition from government loan-repayment road to operating road in the long-term reform.
  • Research on Allocation Efficiency of Highway Transportation Resources in Shaanxi Based on Granger-causality
    RUI Xi-jie, SONG Yu-meng
    China Journal of Highway and Transport. 2017, 30(9): 133-141.
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    To determine the allocation efficiency of highway transportation resources in regional economy definitely and to make a corresponding effective decision based on it, after analyzing the measurement variables on supply of highway transportation and regional economy development, the method of principal component analysis (PCA) was used to reduce the dimensions of standardized data of variables measuring the supply of highway transportation and the regional economy development in Shaanxi from 1993 to 2015, with the purpose of obtaining two sets of synthetic data. By taking the logarithm of two sets of synthetic data to eliminate their heteroscedasticity and reduce fluctuation, Granger-causality test method was applied to their analyses, and the test results were explained by means of economics. The results show that, for any year from 1993 to 2015, the supply of Shaanxi highway transportation of every year in previous three years is the Granger cause of the regional economy development. It is clear that Shaanxi highway transportation supply isn't allocated excessively. On the other hand, Shaanxi regional economy development every year is the Granger cause of the highway transportation supply next year over the whole selected period. It is apparent that Shaanxi highway transportation is in short supply over the whole selected period. To sum up, the highway transportation resource allocation has been under the reasonable level for a long time with respect to the continuous development of regional economy in Shaanxi. In order to make a reasonable allocation of private goods and highway transportation resources as quasi-public goods in Shaanxi regional economy, the supply of Shaanxi highway transportation should greatly increase by planning.
  • Refueling Experiment of On-board Refueling Vapor Recovery（in English）
    HE Ren, DING Hao
    China Journal of Highway and Transport. 2017, 30(9): 142-150.
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    In allusion to the automobile evaporative emission control system with the on-board refueling vapor recovery (ORVR) apparatus, experiments on the influence of fuel temperature, ambient temperature and filling flow on refueling evaporative emission were conducted, based on the refueling experiment criterion of ORVR and the analysis of influencing factors of refueling evaporative emission. The influence of filling pipe diameter and filling flow on liquid seal was discussed with experiments, whilst the liquid seal status was reflected by means of measuring pressure of fluid in the filling pipe. It was necessary to reduce the refueling evaporative emission and propose the approaches to promoting the liquid seal. The refueling process was divided into three stages, namely, liquid seal stage, emission growth stage and the shut-off and refueling stage. Then the analysis focuses on the influence of various factors on liquid seal stage, emission growth stage. The results show that the fuel temperature mainly influences the emission growth stage but the ambient temperature has little effect on emission growth stage. The test suggests that refueling flow should not be too high or too low. It is obvious that filling pipe diameter size and refueling flow can affect formation time of the liquid seal, and the restrictive ring can accelerate the speed of the liquid seal formation. The results provide references for the design of ORVR.
  • Load Spectrum Test Method of Hydraulic Excavator Working Device
    XIANG Qing-yi, LU Peng-min, WANG Bin-hua, ZHANG Hong, XUE Lu
    China Journal of Highway and Transport. 2017, 30(9): 151-158.
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    To provide fundamental data for the fatigue test of hydraulic excavator working device, a load spectrum test method available to reflect actual operation condition of hydraulic excavator was proposed. Based on the test of the cross-section internal force (CSIF), the cross-section was firstly selected at the stress-free location of the bucket rod. Second, the CSIF was fitted by placing strain gauges at the specific measuring points of the cross-section, the pressure and the expansion of each cylinder of the working device were synchronously measured by placing pressure sensors and displacement sensors. Finally, the mechanical equilibrium equation was established to calculate the load-time history of bucket tip and each hinge point, and then the load spectrum of the whole machine or the relevant parts could be deduced from the load-time history. The simulation test and the loading test in the laboratory were carried out to verify the correctness of the method. The results show that the calculated values of the bucket tip load are in good agreement with the simulation values, and the error is less than 3%. The calculated stress values of the specific measuring points of the test cross-section are in good agreement with the test values. The maximum average error is 3.48% under the lateral load, and is 6.46% under the vertical load. The calculated values of bucket tip load are consistent with the test values. The load spectrum acquired by this method is affected by vertical load, the lateral load and the offset load, which is more close to the actual condition. The load spectrum based on CSIS may not be affected by the detailed structure. It is universally applicable to the other types of excavators with similar capacity, and this method can also be used to test the load spectrum of other machines.
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