20 November 2017, Volume 30 Issue 11
    

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    Road Engineering
  • FU Hong-yuan, SHI Zhen-ning, QIU Xiang, ZENG Ling
    China Journal of Highway and Transport. 2017, 30(11): 1-8,98.
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    In order to investigate the water characteristics and deformation regulation of carbonaceous mudstone-soil layered embankment under the water immersion, an indoor model test was carried out to simulate the water level rise outside the embankment. The moisture sensors and ceramic tensiometers were used to measure the water content and pore water pressure at different positions of the embankment. The thrust in the front of the embankment was measured by the soil pressure box. The vertical and horizontal displacement of embankment surface was tested by the micrometer. The results show that the variation of water content in the embankment under the immersion condition can be described as basically unchanged stage, rapidly increasing stage and stable stage. The response time is proportional to the horizontal distance to the embankment surface. Besides, the pore water pressure increases with the increase of water content, and the pore water pressure will be greater than or equal to 0 kPa when the water content reaches saturation. Moreover, the thrust of the embankment decreases slightly in the initial stage of the immersion but increases obviously at the latter stage. The thrust of embankment around the top of the slope is greater than that at the bottom of the slope. The displacement of embankment in the horizontal direction is moving into the slope at first and then outside. As for the vertical direction, the displacement goes down constantly. Furthermore, the water infiltrates in the order of outside to inside, and the bottom to the top. The moving rate of the phreatic line in the carbonaceous mudstone is greater than that in the silty clay.
  • TAN Peng, LING Jian-ming, QIAN Jin-song, CAO Chang-wei, LI Dong-xue
    China Journal of Highway and Transport. 2017, 30(11): 9-17.
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    In order to explore whether the silting phenomenon objectively existed in the fine sand subgrade, and reveal the silting mechanism of fine sand subgrade in coastal area, a model test system device was independently designed and constructed to verify the seepage-migration-silting phenomenon of fine sand filling. Considering the compaction state, moisture condition and rainfall condition of the sand core structure of fine sand subgrade in coastal area, the model test system device was used to investigate the regularity of the permeability, particle gradation and moisture variation of the sand column, which was respectively compacted with fine sand filling and fine sand filling containing fine grained soil under different rainfall intensity and rainfall duration. The results show that, when the rainfall intensity is large enough and rainfall lasts for some time, the infiltration flow will trigger fine sand subgrade silting phenomenon. The permeability coefficients of the whole sand column and the lower sand column tend to decrease steadily, and the permeability coefficient of the upper sand column finally tends to be stable. The decrease of fine group content and the increase of sand group content in the top of the sand column reach the peak, whilst the increase of fine group content and the decrease of sand group content in the bottom of the sand column are the largest. The moisture of each layer of sand column increases from the top to the bottom, and there is obvious dry and wet boundary in sand column. The water retention ability of the bottom fine sand filling is obviously improved, thus causing the obvious decrease of the gravity drainage function of fine sand filling. The macroscopic performance of the phenomenon is the decrease of sand core drainage function and the lower sand core for a long time in the high water content state. The micro performance of the phenomenon is the migration of different layers of fine sand grain group and the silting effect of the migration of grain group in the fine pore channel.
  • CAI Guang-hua, LIU Song-yu, CAO Jing-jing
    China Journal of Highway and Transport. 2017, 30(11): 18-26.
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    To investigate the influence of the initial water content on the strength and electrical resistivity of MgO-carbonated silt, the effect law of the initial water content on the stress-strain, unconfined compressive strength, electrical resistivity, water content, soil pH and electrical conductivity of pore fluid was analyzed by a series of laboratory tests. The correlation between unconfined compressive strength and electrical resistivity was discussed as well. Finally, based on the microscopic test of scanning electron microscopy (SEM), the evolution mechanism of strength and electrical resistivity was clarified. The results indicate that the samples tend to develop from brittleness to plasticity with the increase of the initial water content. Unconfined compressive strength increases with the decrease of the initial water content or the increasing carbonation time. The ratio of deformation modulus to the unconfined compressive strength is about 60-200. The electrical resistivity of MgO-stabilized soil declines with the increase of water content by the power function, and the electrical resistivity of MgO-stabilized silt after carbonation is significantly higher than that before carbonation. The strength and electrical resistivity present a good linear relationship under the specified carbonation time, and hence the electrical resistivity can be used as a simple-effective method for predicting the strength of carbonated soil. With the increasing initial water content, both soil pH and electrical conductivity tend to decrease first and then increase, and reach the minimum at the initial water content of 20% or 25%. The longer the carbonation is, the smaller the soil pH and electrical conductivity are. Moreover, according to the microscopic analysis, it is apparent that the elongated prismatic nesquehonite and flaky dypingite or hydromagnesite exist in carbonated MgO-stabilized soil, and such carbonation products are the main reason for the reduction of water content as well as the increase of dry density, strength and electrical resistivity.
  • CHEN Ming-xiao, LIAO Ping
    China Journal of Highway and Transport. 2017, 30(11): 27-35.
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    To make full use of the increasing strength of the soil between composite foundations piles, and provide a new soft foundation treatment method for the rapid completion of filling the high subgrade in the super soft soil area. The semi rigid pile with drainage capability was used to improve the soft foundation. Through the tests on the ratio of cement mortar and the permeability of earthwork cloth and the characteristics of solid particles, the test pile was carried out on the ground and underground to investigate the solidification characteristics of the cement mortar, the strength characteristics and bending resistance of the pile. In view of the subgrade filling with the height of over 10 m in the soft soil area of the sliding collapse zone of the municipal administration path supported by Nansha procuratorial organs and people's courts, the effects of soft foundation treatment were analyzed by test data including the lateral displacement, settlement, pore water pressure, earth pressure monitoring, the in situ test data of soft soil and the pile detection. The preliminary researches on its design method dependent on the pile bearing capacity test and pile-soil stress ratio were conducted. The results show that the semi rigid pile with drainage capability can accelerate the filling of the subgrade to increase the strength of soft soil and shorten the time of settlement of the soft foundation. During the solidification process of the semi rigid pile with drainage capability, there is a clear separation between cement and sand. Pile cement content significantly increases, and pile radial compressive strength increases gradually. The body presents the similar characteristics of rigid pile. Earthwork cloth around pile plays a role in drainage consolidation, leading to the large settlement. The strength of soft soil around pile dramatically increases, so the frictional resistance around pile in the soft foundation is improved. The bearing capacity of the soil between piles can be given full rein, and the pile can adapt to soft soil settlement and deformation quite well. The body of piles presents characteristics of the flexible pile. The calculation of bearing capacity cannot meet the requirements of embankment load according to the current design of composite foundation theory, thus the use of soft foundation settlement and stability is more suitable for design. It provides the new train of thought for the exploration of the design theory of composite foundation.
  • LIU Da-wei, DAI Zong-hong, CHEN Yang, CHEN Huan-ming
    China Journal of Highway and Transport. 2017, 30(11): 36-44.
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    In order to investigate the stress properties of flexible asphalt pavement generated by the multiple wheel dynamic loads of the heavy vehicle, the finite element model of flexible asphalt pavement considering viscoelasticity was established. The dynamic stress response of flexible asphalt pavement was analyzed under the multiple wheel random dynamic loads and moving constant dynamic loads. The results show that the stress variations of each layer are basically the same in the specific position under two dynamic loads, and the stress variation in each direction is different when the wheels pass through. The longitudinal and transverse stresses of the bottom of Sup25 layer present tensile stress, which are greater than tensile and compressive stresses of other layers in all directions. In the whole pavement, the position and size of the maximum tensile and compressive stresses of each point of the asphalt layers in all directions are not the same. The amplitude variation of the maximum tensile and compressive stresses of each point is large under the random dynamic loads, greater or less than the maximum under the moving constant dynamic loads. Compared with the stresses under the moving constant dynamic loads, the maximum tensile and compressive stresses in three directions of each asphalt layer under the random dynamic loads will increase by 1.63%-20.14% and 2.13%-28.93%. During the course of the research of the dynamic response of flexible pavement, the multiple wheel dynamic loads caused by pavement roughness and its random variations must be considered.
  • ZHOU Xu-hong, LIU Yong-jian, JIANG Lei, ZHANG Ning
    China Journal of Highway and Transport. 2017, 30(11): 45-62.
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    To improve the reliability of confinement effect in concrete filled hollow section tubular structure and force transfer in concrete filled hollow section tubular joint, the concrete filled rectangular hollow section tube (CFRHS) stiffened with PBL was proposed. The existing research results were summarized from mechanical characteristics of the local buckling of steel tube, component, interface and joint. In terms of the limit ratio of width to thickness, axial compression strength, stability under axial load, flexural behavior, eccentric compression behavior, shear-slip constitutive relation, the length of force transfer in joint, bond behavior between concrete and steel tube under fatigue load, static behavior and fatigue behavior of joint, the comparisons with common concrete filled hollow section tube were reviewed and the mechanical advantages of CFRHS stiffened with PBL was systematically demonstrated. The results show that the limit ratio of width to thickness of CFRHS stiffened with PBL is more than twice higher than that of the CFRHS under the axial and eccentric compression, by dint of the supporting function of concrete and stiffening and connective functions of PBL. Compared with CFRHS, the axial strength of the CFRHS stiffened with PBL increases. Meanwhile, PBL guarantees the complete bonding of component, which benefits for the composite action. The axial rigidity and flexural rigidity are improved as well. The concrete tenons in the hole can provide higher shear capacity, whilst the interfacial strength and shear modulus of CFRHS stiffened with PBL twice and 3 times greater than those of CFRHS, respectively. The length of force transfer can be effectively reduced. In addition, the interfacial behavior is good enough under the fatigue load. The stretching resistance of PBL can effectively confine the bending deflection of chord in the joint, thus improving the rigidity and bearing capacity of joints. The hot spot stress concentration factor decreases dramatically in the weld, and the fatigue behavior of joints are improved.
  • HE Shuan-hai, ZHAO Xiang-mo, MA Jian, ZHAO Yu, SONG Huan-sheng, SONG Hong-xun, CHENG Lei, YUAN Zhuo-ya, HUANG Fu-wei, ZHANG Jian, TIAN Bin, WANG Lu-yang, QI Xiu-zhen
    China Journal of Highway and Transport. 2017, 30(11): 63-80.
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    In order to improve the technology of highway bridge inspection and evaluation in China, the current situations and trends of structure inspection and condition assessment of bridges were summarized. Damage of the appearance of the bridge, internal defects, principles of inspection of geometry and mechanical characteristics, content and methods of inspection were analyzed in detail. Meanwhile, current situations of the comprehensive inspection technology of prestressed force for PC bridges were commented. Meanwhile, the methods for safety evaluation of in-service RC bridges and PC bridges were summarized, with a summary of the latest research results of the evaluation of fatigue life capability for steel bridge. The comprehensive analyses show that, the intelligent nondestructive testing is the development trend of bridge inspection technology. The intelligent inspection technologies, such as image recognition and sonic CT technology, are widely applied to the inspection of damage of the bridge appearance and internal defects. Comprehensive prestressed inspection technology characterized by prestressed positioning, corrosion, grouting compactness and the tension of prestressed tendon provides a significant method to evaluate the bearing capacity of in-service prestressed concrete. As for the evaluation technology of concrete bridge, the concrete bridge damage evaluation method featured by crack properties, and prestressed condition extends the possibility of quantitative evaluations for the safety of in-service damaged concrete bridge. Finally, in the evaluation of the fatigue life capability of the steel bridge, the nominal stress method based on S-N curve of structural fatigue detail is the major method for evaluation. Whereas, the fracture mechanics method featured on the modern crack detection technology is promising in the evaluation of the fatigue life capability of the steel bridge.
  • LI Shou-ying, YAN Jie-tao, XIAO Chun-yun, CHEN Zheng-qing
    China Journal of Highway and Transport. 2017, 30(11): 81-88.
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    Wake galloping is a kind of large amplitude vibration of the hangers always observed on large-span suspension bridges. In order to investigate the unsteady aerodynamic forces on the strand in the wake, two smooth ridge circular cylinder models were made and tested in the wind tunnel tests to measure the aerodynamic forces on the test model by a forced vibration system developed by HD-2 wind tunnel, on which the wake galloping reappeared. The lift and drag force histories, together with the displacement histories, were directly measured in the wind tunnel tests. Eight relative aerodynamic derivatives of the strand in the wake were simultaneously identified. The relationships between eight aerodynamic derivatives and reduced wind velocity in different cases are discussed, and the accuracy of unsteady aerodynamic forces integrated by aerodynamic derivatives is proved. The results show that the aerodynamic stiffness terms H4* and H6* have quite large positive values under high wind speed, and could cause negative aerodynamic stiffness in across-wind direction and enlarge the vibration amplitude of the strand. The aerodynamic stiffness terms P4* and P6* only have positive values in few cases. The wake-induced ellipse movement trajectories of the strand in the wake are determined by eight aerodynamic derivations. The unsteady aerodynamic forces obtained through aerodynamic derivatives agree well with that tested directly. The aerodynamic derivatives could be utilized to determine aerodynamic stiffness forces and aerodynamic damping forces for further investigation on wake galloping.
  • Bridge and Tunnel Engineering
  • LIU Yang, LI Ming, DENG Yang, WANG Da
    China Journal of Highway and Transport. 2017, 30(11): 89-98.
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    To provide a reference for the design and operation management of steel deck welding details, the fatigue reliability of steel bridge deck welding details was investigated in allusion to the steel deck welding under the action of random vehicle load. The influence of traffic growth, the correlation between axle load and long-term effects of pavement temperature were taken into the consideration. Based on WIM measured data of the steel box girder suspension bridge, the distribution characteristics of the random vehicle parameters, especially the correlation between vehicle axle loads, were analyzed. The random vehicle simulation with multi parameters was programmed by nonparametric kernel density estimation-Copula axle load sampling method, considering the correlation between axle loads. The influence of the pavement temperature and the correlation of the vehicle axle load on fatigue load effects was analyzed by dint of the finite element method. Finally, the function was established based on the fatigue damage theory. The fatigue reliability was calculated by MC method, and the influence of traffic growth, correlation of the axle load and long-term effect of pavement temperature on the fatigue reliability of steel deck welding details was analyzed. The results show that the axle load has the characteristics of multimodal distribution, and there is a strong correlation between axle loads. Without considering the correlation between axle loads, greater errors will be caused when simulating random vehicles. Pavement temperature changes mainly affect the stress amplitude of the steel deck welding details, with a little influence on the cycle numbers and the stress amplitude reduction coefficient in consideration of the transverse position of the wheel. Considering the long term effect of pavement temperature, the probability density function of daily equivalent stress amplitude presents multi peaks. The daily equivalent stress amplitude mean considering the correlation of axle load is much larger than that without taking the correlation between axle loads into consideration. The traffic growth has little effect on the fatigue reliability of in the initial stage of the structure, thus causing the rapid decrease of the fatigue reliability in the later stage. The correlation of the axle load and the long term effect of pavement temperature will decrease the steel deck welding details fatigue reliability, and the influence of correlation of the axle load on the fatigue reliability is more obvious than the long term effect of pavement temperature.
  • ZHANG Nan, WANG Hui, CHEN Xu, CHEN Jia-jia, SHA Xiao-xiao
    China Journal of Highway and Transport. 2017, 30(11): 99-107.
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    In order to research the action of embedded steel on improving anti-impact performance of concrete bridge piers, the transverse static load tests and the horizontal impact load tests of three steel reinforced concrete piers and one reinforced concrete pier were conducted. The factors affecting impact failure modes were analyzed. The influence of embedded steel types on the strain increase of pier body and impact crack and impact shear strength were investigated. By dint of the superposition principle of static shear strength of concrete pier, the factors of concrete shear strength and strain rate effects of materials were reasonably considered. The calculation formulas which predict impact dynamic shear strength of steel reinforced concrete piers were established by the impact dynamic strength of materials. The research results show that the impact crack peak forces of concrete piers embedding steel angle, channel steel, and circular steel tube increase by 98.76%, 194.22%, and 186.76%, respectively, and the impact failure peak forces increase by 19.82%, 52.83%, and 46.22%, respectively, than that of concrete piers. Embedded steels have remarkably improved the anti-impact crack ability and anti-impact strength of concrete piers. The impact crack peak forces and impact failure peak forces of concrete piers embedding channel steel and circular steel tube increase by 48.03%, 44.27%, and 27.55%, 22.03%, respectively, than that of concrete piers embedding steel angle. The concrete piers embedding channel steel and circular steel tube are steel reinforced concrete piers with good anti-impact performances. The calculated results are in good agreement with experimental results, which will provide references for the anti-impact strength design of steel reinforced concrete bridge piers.
  • LIU Xiao-bing, LI Shao-jie, YANG Qun, LIU Qing-kuan
    China Journal of Highway and Transport. 2017, 30(11): 108-114.
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    In order to provide a reference for wind load value of twin parallel box girders in the specific engineering, pressure-measured wind tunnel tests of sectional models of twin parallel flat box girders and twin parallel bluff box girders were conducted. Drag coefficients of twin box girders with 15 different spaces under 11 different wind attacking angles were measured and compared with that of single box girder. The wind attacking angle ranged from -10° to 10°. The ratio of net spacing of twin box girders to the width of single box girder (D/B) ranged from 0.025 to 6. The interference factor was defined as the ratio of drag coefficient of forward (or leeward) box girder to that of single box girder. Aerodynamic interference effect on drag coefficient of twin parallel box girders was researched quantitatively. The interference factor of the drag coefficient was influenced by the wind attacking angle and spacing, whilst the contours of the interference factor were shown for the first time. The results show that the influence of the aerodynamic interference effect on drag coefficient of forward box girder is slight. The interference factors of forward flat box girder and forward bluff box girder range from 0.75 to 1.30 and 0.88 to 1.20, respectively. The influence of the aerodynamic interference effect on drag coefficient of leeward box girder is obvious, showing as the reducing effect. Such reducing effect is more notable in small spacing. Compared with the leeward flat box girder, the reducing interference effect on leeward bluff box girder is more remarkable. The minimum interference factor of leeward bluff box girder is around -0.3. The reducing effect on leeward bluff box girder cannot be neglected even when D/B=6.
  • CAO Li-bo, CHEN Zheng, QIN Qin, YAN Ling-bo
    China Journal of Highway and Transport. 2017, 30(11): 115-121,128.
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    In order to achieve low-cost self-driving in bus rapid transit system, an automatic rapid transit system based on vehicle position sensing was proposed. This system consisted of sensing layer, decision layer, control layer and execution layer. Sensing layer by dint of the vision system and GPS would perceive the overall lateral and longitudinal positions of the vehicle on the road. Then, the ultra-wideband communication and ranging between vehicle-vehicle and vehicle-infrastructures were used to obtain accurate position of surrounding vehicles and infrastructures relative to the ego-vehicle. The lateral positioning approach, followed by GPS/DGPS overall positioning, vehicle-vehicle and vehicle-infrastructure relative positioning algorithms, was described in detail. Based on the position sensing, approaches to accomplishing key processes of self-driving such as tracking, parking and overtaking were presented. Besides, the feasibility of the system was analyzed. Its economy advantage compared with traditional positioning solutions and its high accuracy in the typical condition were demonstrated. The results show that the proposed rapid transit vehicle can obtain the accurate positions of itself and surroundings using relatively inexpensive devices and simple algorithms, and help achieve the control of self driving processes. The results prove the bright prospect of bus rapid transit system.
  • ZHAO Xiao-hua, CHI Jing-hao, FAN Zhao-dong, RONG Jian
    China Journal of Highway and Transport. 2017, 30(11): 122-128.
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    In order to reduce traffic accidents and improve the comprehensive operation level of the road intersection, this paper was aimed at the utility evaluation and the optimization of traffic safety devices at the road intersection. The effective evaluation and optimal selection of the traffic safety combination devices were realized based on the micro-driving behavior data at the road intersection. Firstly, the highway intersections were classified by dint of highway crossing patterns, the width of crossed highways, and traffic signal types, whilst traffic safety devices were classified into ten sub-types based on their functions. Secondly, according to the analysis of the field observation, different traffic safety devices assemblies were designed corresponding to existing problems at distinct types of intersections, thus forming 3 or 4 corresponding schemes. Then, by means of driving simulation experiment, nine evaluation indicators were selected to assess the effects of traffic safety devices at highway intersections from the perspectives of security, foreseeability and comfortableness. Based on that, the optimized installation model of traffic safety devices of the highway intersection was suggested. Finally, the typical highway arterial intersections were selected to analyze as the case to realize the optimized installation devices. The results show that this method is practical in addressing issues like the deployment of traffic safety devices at highway intersections, and lays the foundation of forming the optimized combination installation of highway intersection traffic safety devices in various types of intersection. Te results provide the basis for designing a manual for traffic safety device installation at the arterial intersections.
  • SHANGGUAN Wei, ZHANG Feng-jiao, CAI Bai-gen, WANG Jian
    China Journal of Highway and Transport. 2017, 30(11): 129-137,155.
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    In order to test the function of cooperative vehicle infrastructure system (CVIS) effectively and improve its effect, the test sequence optimization method was investigated. According to the functional requirement analysis of CVIS, typical application scenarios containing multiple intersections, multiple sections and multiple vehicles were constructed. Then, functional characteristics were illustrated by the analysis of typical application scenarios with fault tree analysis (FTA). Moreover, test cases based on functional characteristics of CVIS were established. The test sequences of simulation test in light of CVIS were generated by a modeling analysis by dint of the method of labeled-ports time input/output automata (Lp-TIOA) and the modeling tool of UPPAAL. Besides, test sequences generated by the Lp-TIOA modeling were optimized by firefly algorithm and immunity algorithm (IFA) proposed in this paper. Meanwhile, the effect of test was assessed from the degree of coverage, redundancy and quickness. The results show that the coverage can be ensured to be 100% by the optimizing algorithm, the redundancy decreases to 82%, and test time is shorten to 10 s when the number of scenario states is large. The test sequence optimization is fruitful in reducing the test redundancy based on the IFA and the IFA is faster and more effective to reduce the test redundancy than TIOA. It follows that the optimization result is better than the original sequence generated by timed automata. The test efficiency can be increased with the decrease of the redundancy. Therefore, the test sequence optimization algorithm is feasible.
  • ZHANG Jia-qi
    China Journal of Highway and Transport. 2017, 30(11): 138-146.
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    In order to take autonomous vehicles to the destination efficiently with no collision, the problem of impossibility of highlighting advantages of both global and local paths at the same time was deduced. The environment around autonomous vehicles was detected by dint of the laser sensor, whilst the plane environment was divided into left and right half planes by the connection of sub-target point and autonomous vehicles. After searching and evaluating the accessible free sectors based on a cost function, the optimal paths were selected. In view of the different vehicle conditions at different time, a risk assessment function was established based on the distance between congested area and the autonomous vehicle, and the current vehicle speed to guarantee the optimal path with no collision. The fuzzy control was established, on the basis of driving behaviors, regarding the risk assessment value and angle into the optimal sector as the input, and angular velocity and the linear velocity of vehicles as the output. Meanwhile, with the global path known, the sub-target was selected for the real-time local path planning on the global path. On account of the influence of environment and other factors, the sub-target was classified into the place blocked by the unknown area, somewhere obstructed by the known congested area with visible sub-target and somewhere blocked by known area with invisible sub-target. In order to guide the autonomous vehicles, the state of each sub-target was analyzed respectively, and vehicles should move forward at the certain speed in a certain direction. The results show that the proposed method tends to solve the problem of no foresight in the local path planning. The sub-target on the global path can effectively guide the vehicle to the final target without any collision, sheltering the vehicle from obstacles. Such a method ensures the optimal real-time path of autonomous vehicles, and correlates the global path planning layer with the local path planning layer.
  • YAN Jian-bo, SHI Pei-long, YU Qiang, LIU Feng-yun
    China Journal of Highway and Transport. 2017, 30(11): 147-155.
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    In order to effectively reduce the working frequency of service brake and labor intensity of the driver on long downhill sections for heavy duty truck, the graded control strategy was proposed based on the continuous braking matching level and the deceleration estimation model of the generalized growth and pruning radial basis function (GGAP-RBF) neural network. Firstly, regarding the heavy duty truck as a research object, the relation curve between continuous braking force and running speed was investigated, based on the tests of the engine braking, exhaust braking and eddy current retarder braking. Furthermore, the deceleration estimation model was established, based on GGAP-RBF neural network with the current speed, vehicle speed difference and road gradient as input parameters and demand deceleration as output parameter. Then the minimum brake force difference between demanding braking force and level braking force was set to be the principle to match the braking levels. Finally, the validity of control strategy was verified by the mean of simulation and tests on the fixed slope and variable slope road conditions. The results show that with the same velocity changes under condition of slope of 4.2%, the continuous braking grade only shifts twice, by dint of the control strategy proposed in this paper, less than that of the experienced driver. Under the changing-slope working condition of 13 160 m, the velocity can decrease steadily and then reach the desired value after 150 m. Then the velocity ranges from 60 to 62 km·h-1. It can be seen that it holds the strong adaptability feature. The strategy proposed in this paper can reduce the service braking working frequency and drive intensity effectively on the basis of the continuous braking grading control, and velocity reduction and the velocity holding effectiveness on downhill condition can be achieved.
  • WU Xue-bin, ZHANG Xin, CHEN Hong-wei
    China Journal of Highway and Transport. 2017, 30(11): 156-162.
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    In order to realize the transmitting torque modeling of automatic diaphragm spring clutch for hybrid electric vehicle,the diaphragm spring clutch applying to a hybrid electric bus was taken as the research object, and the elastic characteristic calculation model of diaphragm spring based on A-L method was established. Meanwhile, the load deformation characteristics of the clutch cover and follower disk were tested. Considering the influence of the deformation of follower disk, clutch cover and diaphragm spring on the clutch operation, the static deformation coupling relationship of the clutch diaphragm spring was analyzed.The analytical expression of the relationship between the disengage travel of the diaphragm spring clutch and the deformation of the clutch parts was derived, A static calculation model of clutch operating characteristics was presented, taking the disengage travel as the input and the pressing or separation force as the output.Taking the clutch sliding speed and sliding friction temperature as the test factors, and the friction coefficient of the clutch friction plate as the test target, the orthogonal test scheme with two factors and three levels was designed. The friction coefficient test of the clutch was carried out on the clutch comprehensive tester.A polynomial form regression equation was obtained by the calculation and analysis of test data and an empirical model of the clutch friction coefficient with sliding speed and sliding temperature was established. The clutch transmitting torque model was put forward based on the operating model of the compression force and the empirical model of the friction coefficient.Through clutch bench test, the calculation results of clutch transmitting torque model and bench test results were compared and analyzed. The results show that the regression model of the friction coefficient fits well, and the confidence coefficient is 99%. The error of the transmitting torque model of the bus diaphragm spring clutch is large in the range of large rotate speed differences, whilst in the range of small rotate speed differences, the calculation accuracy is high. The presented model can effectively predict the clutch transmitting torque.
  • LIU Dong-hai, WU You
    China Journal of Highway and Transport. 2017, 30(11): 163-169.
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    To realize continuous measuring and real-time visualization monitoring of the pavement lift thickness, and reduce measuring errors caused by human behaviors, a real-time lift-thickness acquisition device applicable to the highway construction was developed by dint of traditional methods of pavement lift-thickness measurement. Meanwhile, a method for continuous measuring and real-time visualization monitoring of pavement lift thickness was proposed. Based on the device, the geometrical space relationship between datum plane before paving and pavement surface after paving was established to calculate the lift thickness. A method for integrating monitoring information by means of three-dimensional web-based visualization and the ActiveX technology was proposed, and the corresponding system was developed. The system could monitor and update the information of lift thickness on the Web client. When the calculated lift thickness was not satisfied with the design control standard, the warning message would be sent out. The results show that the method has the feature in wide applicability, and the absolute deviation of the calculated lift thickness is less than 0.3 cm within the permissible error range. The weak area can be visualized to inform the operators by issuing a warning message, and provide specific instructions in the real-time adjustment. This new system can monitor the lift-thickness in a continuous, automatic, accurate, and three-dimensional visualized manner, thus realizing the collaborated "operator-contractor-supervisor-owner" streamline quality control mode. The system provides an advanced technique for all parts participating in the project construction to control road pavement quality.
  • GU Hai-rong, DONG Qiang-zhu, LIANG Feng-dian, LI Jin-ping, JIAO Sheng-jie
    China Journal of Highway and Transport. 2017, 30(11): 170-176.
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    To deal with the slow heating speed for asphalt pavement recycling which seriously affects the increase of the whole recycling speed,the method on improving the asphalt pavement heating speed was researched by changing the construction technology. The numerical analysis model was established, the change of temperature fields in the asphalt pavement during the heating was calculated by the single-stage technology and the multi-stage technology. The results of numerical analysis were verified by simulation experiments in the laboratory. The research results indicate that, the main reasons for the slow heating speed exist in the big temperature gradient for the low heat conductivity of the asphalt pavement and the thickness in the single-stage hot in-place recycling. The method used in multi-stage technology can increase the asphalt pavement heating speed obviously by removing away the heated upper materials and inputting the heat energy from the inner to heat the asphalt pavement layer by layer quickly and efficiently. The influence of the thickness and heat-transfer coefficients of the pavement on the asphalt pavement heating speed becomes fewer and fewer. For heating the 4cm asphalt pavement, only 43% of time and 70% of energy are needed in the multi-stage asphalt recycling technology as that in the single-stage technology.