20 August 2018, Volume 31 Issue 8
    

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  • MA Jian, LIU Xiao-dong, CHEN Yi-song, WANG Gui-ping, ZHAO Xuan, HE Yi-lin, XU Shi-wei, ZHANG Kai, ZHANG Yi-xi
    China Journal of Highway and Transport. 2018, 31(8): 1-19.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To promote the development of China's new energy automobile industry and technology, the current status of several key links in China's new energy automobile industrial chain, including the integrated industry of new energy vehicles, key components, and infrastructures were systematically reviewed in this article, starting from the development status of domestic new energy vehicles. In addition to the progress made in domestic new energy vehicle technology, progress in power battery technology, driving motor technology, and fuel cell technology were summarized. Next, the gaps and deficiencies in the development of new energy vehicles in China were analyzed and summarized by benchmarking the technological frontiers of international pure electric vehicles, plug-in hybrid electric vehicles, fuel cell vehicles, power battery, and driving system. Based on the analysis of the current status, the existing problems in the development of new energy vehicles in China were extensively analyzed from six different aspects, namely strategic policy, core technology, research and development production, industrial system, demonstration and promotion, and product sales. Furthermore, the countermeasures and suggestions for the future industrial development of China's new energy vehicles and directions for technological breakthroughs were provided from six different aspects, namely top layer design, independent innovation, basic support, industrial ecology, support system, and business model. Finally, the development paths of domestic new energy automobile industry and technology for the future were discussed. In terms of industrial layout, enterprises dealing with vehicles and their related parts should be rationally arranged to promote enterprise clustering and industrial agglomeration. For pure electric vehicles, the development of an integrated electric chassis and the new power battery system should be prioritized. For plug-in hybrid electric vehicles, attention should be focused on high-performance hybrid powertrains and the dedicated engines and dynamic coordinated control technologies. For fuel cell vehicles, the development of fuel cell stacks and key materials should be the focus while considering the development of fuel cell systems and core components.
  • LI Lian-xiang, LI Xian-jun, CHENG Xiao-yang, HUANG Heng-li
    China Journal of Highway and Transport. 2018, 31(8): 20-29.
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    To obtain the mechanics behavior at an enlarged-part and predict the pile settlement when a squeezed and branch pile was vertical loaded, the relationship between the force and displacement at the enlarged-part was solved by using the cavity expansion theory, and the load transfer method was applied to the squeezed and branch pile. When a pile is vertically compressed, the enlarged-part will squeeze the soil and move downward, which can be regarded as a cavity expansion problem. Based on a rational assumption, the relationship between the enlarged-part horizontal internal pressure and the vertical displacement was deduced. From the mechanical analysis on the subsurface, a varying pattern of the pile-soil contact surface, A'C, and relationship between the enlarged-part resistance and vertical displacement were confirmed, and some influential parameters were also researched. Based on the above, by applying a hyperbolic model and linear elastic model in the pile shaft and pile tip, respectively, the load transfer method was applied to the squeezed and branch pile to obtain the pile-head settlement curve and pile inner force. The research result shows that by using the cavity expansion theory, the approach for obtaining the relationship between the enlarged-part resistance and vertical displacement completely considers the soil squeezing effect and geometric construction features of the enlarged-part. The enlarged-part resistance is more sensitive to the squeezed angle, which is in more accordance with engineering practices. The enlarged-part horizontal internal pressure has a nonlinear distribution on the reversed-truncated cone-shaped subsurface and decreases with the increase in the initial radius, and the nonlinearity becomes more obvious as the vertical displacement increases. The value of the enlarged-part horizontal internal pressure increases as the vertical displacement increases, but decreases with the increase in the squeezed angle. The load transfer method for squeezed and branch piles considering the cavity expansion theory can determine the settlement and mechanics behavior effectively. Regarding the squeezed and branch piles, the variation in the enlarged-part resistance caused by the squeezed angle has a stronger effect on the final bearing capacity than the simple side-resistance variation. The relevant method and conclusions can provide references for engineering.
  • LIU Song-yu, CAO Jing-jing, CAI Guang-hua, ZHANG Zheng-fu
    China Journal of Highway and Transport. 2018, 31(8): 30-38.
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    Reactive magnesia (MgO)is considered as a novel material used in soft soil stabilization, and the soil strength is significantly improved in several hours when the soil is admixed with reactive MgO and then subjected to carbonation of gaseous CO2. On the basis of existing studies, reactive MgO-stabilized soil samples were prepared under the conditions of five different compaction degrees of 86%, 87%, 89%, 91%, and 92% using the static pressure method, and then the laboratory carbonation experiments of the MgO-stabilized soil samples were performed. Some tests for those pre-or post-carbonation MgO-stabilized samples were conducted including the tests of the moisture content, dry density, and unconfined compressive strength in order to study study the influence law of the compaction degree on the moisture content, dry density, and unconfined compressive strength of the MgO-carbonated soils. Finally, typical samples were chosen from the broken specimens after the unconfined compression tests, and the micro structural characteristics of the carbonated soils were analyzed from the aspects of the carbonation products and pore characteristics via the X-ray diffraction, thermo gravimetric, scanning electron microscope, and mercury injection tests. The results indicate that a large amount of CO2 and water are consumed when the reactive MgO-stabilized soils are subjected to CO2 carbonation, and the main carbonation products are prismatic nesquehonite and flaky dypingite/hydromagnesite, which have significant cementing and filling effects, facilitating the obvious improvement of the dry density and strength of the carbonated reactive MgO-stabilized soils. The initial compaction degree of the MgO-stabilized soils has a significant impact on the carbonation effect. With the increase in the initial compaction degree, the water content of the carbonated soils shows the trend of first increasing and then decreasing, whereas the unconfined compressive strength exhibits the opposite trends. When the initial compaction degree reaches the medium compaction degree of 89%,the water content of the carbonated samples is the lowest and most carbonation products are formed, leading to the largest unconfined compressive strength as well as the smallest porosity of the carbonated samples. Moreover, the compaction degree of 89% is demonstrated to be the best initial compaction degree and most beneficial for the carbonation of MgO-stabilized soil.
  • LI Shun-qun, CHEN Zhi-xiang, XIA Jin-hong, GUI Chao
    China Journal of Highway and Transport. 2018, 31(8): 39-46.
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    An aggregation geometric model is established based on homogeneous spherical particles to reveal the variation in the thermal conductivity in the process of soil freezing. The model is composed of multiple spherical soil particles having equal radius, which are stacked in the orthogonal direction, and the remaining area is filled with liquid water. Based on the objective law that pore water begins to freeze in the region away from the soil particles, the aggregation model of the frozen core in the center of the spherical particles and the outward expansion of the concentric spheres are established. In view of the three-phase composition of soil particles, water, and ice, the mixed flow calculation method for thermal conductivity is proposed according to the microscopic properties such as the composition of the saturated frozen soil and contact between spherical particles. Based on the results of the homogeneous spherical aggregation geometry model and unfrozen water content of the frozen soil, the thermal conductivity of the frozen soil at different negative temperatures can be determined by using the method of mixed flow calculation, as proposed in this paper. A modified orthogonal heat conduction geometry model is proposed to satisfy the calculation of thermal conductivity at different dry densities of the soil. The predicted values for the flow calculation method were respectively compared with the predicted values of the Johansen method, Wiener method, and measured values of the probe method. The result shows that the mixed flow calculation method proposed in this paper can accurately predict the thermal conductivity of frozen sand in the high-temperature frozen stage. The aggregation geometric model explains the phenomenon that the thermal conductivity of the soil with a higher dry density is not necessarily increased after freezing. It concretely shows that the thermal conductivity of the frozen soil varies with different negative temperatures is the dynamic change in the ice content in the soil. Concurrently, the mixed flow calculation method established based on the location of the frozen nucleus provides the physical significance of the Wiener method for the prediction of the frozen soil thermal conductivity. The aggregation model and mixed flow calculation method for thermal conductivity can reliably predict the thermal conductivity of frozen soil at different negative temperatures. It is expected to ensure the study of the moisture-heat-stress coupling problem in the cold zone and freezing process.
  • CHENG Ze-hai, SONG Ze-yuan, HUANG Bo, LING Dao-sheng
    China Journal of Highway and Transport. 2018, 31(8): 47-57,103.
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    Under the effect of some factors such as the stress, particle composition, and moisture content, the deformation characteristics of gravelly soil mingled with clay materials are very complex. This type of soil is widely used in subgrade filling engineering. In the field construction, the composition of the filler fluctuates significantly, and so, the research on the effect of the mechanical properties of gravelly soil mixed with clay is of tremendous significance in engineering design. For the purpose of compaction, gravelly soil is used in the construction of an airport runway, and the influence of the gravel content and fine content on the mechanical properties of compacted gravelly soil is analyzed by a series of medium triaxial compression tests. In addition, its shear strength and deformation characteristics under the three different conditions of unconsolidated undrained, consolidated undrained, and consolidated drained are studied. Concurrently, the effect of different sampling water contents on the shear strength of compacted gravelly soil is studied. The test results show that the compaction of gravelly soil exhibits a strong shear expansion under a low confining pressure. Under the unconsolidated undrained (UU) triaxial compression test, the strength of compacted gravelly soil with small fine particles depends on the interlock force of the large particle size. It is in proportion to the gravel content; the initial moisture content of the mixture has a significant effect on the strength of the compacted gravelly soil, and the clay grain in the particle group could be easily slid with a moisture content higher than the optimum moisture content, influencing the stress-strain behaviour and significantly reducing the shear strength of the compacted gravelly soil. Moreover, there is no direct relation between the strength of the gravelly soil and gravel content under saturated consolidation. High gravel content does not represent the absolute high strength, and the rational particle grade is an important factor in determining the strength of the specimens under consolidated undrained(CU) and consolidated drained (CD) triaxial compression test. The increase in the clay content of the compacted gravelly soil will lead to a decrease in its strength. Moreover, the gravel content and clay content have little effect on the critical state of compacted gravelly soil. The critical stress ratio of compacted gravelly soil with the same mineral composition and different particle composition is 1.73 under the CU and CD tests.
  • ZHANG Hai-tao, LIANG Shuang, YANG Hong-sheng, YU Li-ze
    China Journal of Highway and Transport. 2018, 31(8): 58-65.
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    Vibration mixing technology has been used in the domestic design and construction of the base materials of cement-stabilized crushed stone. Vibration mixing technology is effective for cement-stabilized macadam mixture mixing, causing cement to be better dispersed in the mixtures; consequently, it has been widely applied. However, the mixing equipment for cement-stabilized macadam mixtures is a large vibration mixer on the construction site. Thus, in the proportion design of cement-stabilized crushed stone, there are no indoor vibration mixing equipment, and it is not possible to accurately analyze the indices of cement-stabilized crushed stone between vibration mixing and non-vibration mixing. In relation to practical projects, the objective of this study is attempt the simulation of the vibration mixing equipment of cement-stabilized crushed stone on site by the modification of the indoor aggregate vibration sieve. Through a series of tests, the equivalent relationship between the modified indoor vibration mixing equipment and vibration mixing equipment on site is established. The research contents include:principle and parametric analysis of the indoor vibration mixer, proportion design of cement-stabilized crushed stone based on indoor vibration mixing, and comparative analysis of the compressive strength of cement-stabilized crushed stone between indoor vibration mixing and vibration mixing on site. The research results show that the proportion design of cement-stabilized crushed stone by performing indoor vibration mixing is better than that with vibration mixing on site, and the unconfined compressive strength of the cement-stabilized crushed stone obtained by indoor vibration mixing is larger than that by vibration mixing on site. According to the test results, the optimum mixing time is achieved with the modified indoor vibration mixing equipment for the cement-stabilized macadam mixture. The modified indoor vibration mixer reaches the efficiency of the vibration mixer on site and achieves satisfactory results. Thus, vibration mixing technology can be applied in the proportion design and construction of cement-stabilized crushed stone.
  • CAO Dan-dan, ZHAO Yan-qing, KONG Fan-sheng, WANG Guo-zhong
    China Journal of Highway and Transport. 2018, 31(8): 66-73.
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    The objective of this study is to provide reference for the backcalculation of asphalt pavements with a rigid base. Aiming at asphalt pavements with a rigid base, the spectral element method was used as the forward analysis engine, and then the optimized objective function was constructed using the measured and computed deflection time history. The layer parameters of the asphalt pavement were backcalculated using a numerical optimization method. Accordingly, the backcalculated results were compared with those obtained using the traditional static method. The results indicate that the backcalculated results from the traditional static method contain the elastic modulus of each layer. The dynamic modulus master curve and phase angle master curve of asphalt layers as well as the elastic moduli of other layers can be backcalculated from the dynamic method. The dynamic modulus master curve and phase angle master curve compose the complete viscoelastic parameters, which can completely represent the relationship between the viscoelastic property of the asphalt concrete and loading frequency. The dynamic backcalculation method uses the entire measured deflection time history at various sensor locations as the constraints in the optimization process. In comparison, the static method uses only the peak deflections as the constraints, so that its optimized constrain power is significantly lower than that of the dynamic method. The coefficient of variance (COV) of the backcalculated results from the static method is also larger than that from the dynamic method. Specifically for the base and subbase layers, the COV of the backcalculated results from the static method is more than twice that from the dynamic method. Hence, the percentage of the backcalculated result in the typical reasonable range is significantly smaller than those from dynamic method. The static backcalculation method is vulnerable to cause the "modulus-transferring" phenomenon, which will lead to distortion of the backcalculated result and prevent the objective assessment of the layer condition of the asphalt pavement. The dynamic backcalculation method could utilize the full information contained in the measured deflection time history, which could lead optimized results to actual values, avoid the "modulus-transferring" phenomenon and provide more effective approach for pavement quality assessment.
  • LIU Shi-fu, LING Jian-ming, YANG Wen-chen, YUAN Jie
    China Journal of Highway and Transport. 2018, 31(8): 74-81.
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    To solve some of the shortcomings of rigid pavement structure parameters back-calculation method of area of the deflection basin (AREA), such as inadequate use of deflection information of each sensor, multiple solutions of the structural parameters, and large error of fitting, this paper presented the back-calculation of rigid pavement parameters using the average distance of deflection basin (DBADM) and its comprehensive analysis. On the basis of modeling and analyzing the traditional AREA thoroughly, an index of the DBADM was proposed to calculate the radius of relative stiffness by using the deflection information of each sensor. Subsequently, the modulus of the subgrade reaction was calculated to minimize the error of the filed-test deflection basin. With the above two features, the DBADM theoretically solves the problem of multiple back-calculation solutions of traditional AREA. Taking the typical structure of a rigid pavement as a study example, the sensitivity, robustness, and computational efficiency of the DBADM are comprehensively investigated in comparison with the state-of-art AREA and Lin method. The numerical analysis results demonstrate that the DBADM has nearly identical sensitivity to each sensor deflection and it improves the robustness significantly, and the back-calculation error is less than 12% within 5% error of some sensor deflection. The DBADM has more robustness to the measured error of each sensor, and can respectively improve 42.5% and 33.5% with respect to AREA and the Lin method. With respect to the computing efficiency, the DBADM is almost equivalent to AREA and is seven times more efficient than the Lin method. Based on the field Falling Weight Deflectometer (FWD) data of 4C and 4D airports, the back-calculation results demonstrate that the DBADM has the ability to decrease the fitting error of the measured deflection and improve the accuracy of the back-calculation parameters.
  • WANG Jun-jie, LIU Hui-jie, YIN Hai-jiao
    China Journal of Highway and Transport. 2018, 31(8): 82-93.
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    In this study, six barge finite element models were developed and rigid cylinders were used to simulate the impact process to establish a simplified method considering the impact effect. Then, 252 samples of history curves of the impact force under different velocities and radius-width ratios were obtained by numerical simulations. A modified half-wave sine function was used to simplify the history curves of the impact force. The specific parameters of the model were determined by mathematical statistics. Therefore, the impact load curve can be directly determined based on barge tonnage, impact speed, impact ratio, and other factors. The error analysis indicates good accuracy of the model parameters. Three types of errors of the modified half wave sine load model were identified, and dynamic response analysis was carried out using two bridge models of different structural features. The accuracy of the calculation results of the simplified load model was analyzed and compared with the dynamic response of barge contact collision, which is regarded as the exact solution. The error contributions of the simplified load model were discussed. A comparison of the calculation results of two bridges indicates that the modified half-wave sine load model has good accuracy for the dynamic analysis of both flexible and rigid structures. In conclusion, this modified half-wave sine load model has some significance for practical engineering applications.
  • SHAO Xu-dong, QU Wan-tong, CAO Jun-hui, YAO You-lin
    China Journal of Highway and Transport. 2018, 31(8): 94-103.
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    A lightweight composite bridge deck (LCD) consisting of an orthotropic steel deck stiffened with super toughness concrete (STC) was proposed in order to solve the problems of fatigue crack, and damage in paving in orthotropic steel deck. In this study, we have considered optimizing the system because the stiffness of bridge deck is significantly improved. The proposed LCD would have large U-ribs replacing the traditional U-ribs. Compared to the LCD with traditional U-ribs, the one with large U-ribs has many advantages:the cost of steel is slightly changed, while the weld length is reduced by 36%, indicating relatively easy welding and a decrease in the amount of weld defect, and further solving the problem of fatigue cracking. Considering a bridge with steel box girder as an example, local finite element models with four different systems were established to investigate the six fatigue details using hot spot stress method. Our results indicate that the stress amplitudes of six fatigue details between LCD with large U-ribs and the one with traditional U-ribs are nearly the same, and the decreasing ranges of stress amplitude are very close. Meanwhile, the results of the finite element analysis suggest that the STC layer in LCD with large U-ribs has a good transverse mechanistic performance, and the studs show a good fatigue property. Finally, in order to investigate the longitudinal flexural tensile performance of the STC layer, a negative bending full-scale test was conducted. The crack stress in the top layer of STC was found to be 24.1 MPa, which is much higher than the calculated tensile stress of 10.92 MPa. The study, thus, implies that LCDs with large U-ribs have good fatigue and static behavior.
  • DAI Guo-liang, DAI Hao, YANG Yan-hua, GONG Wei-ming, HE Hong-nan
    China Journal of Highway and Transport. 2018, 31(8): 104-112.
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    The traditional method of investigating the effect of scouring on the foundation bearing capacity usually adopts an approach that removes the scoured soil above the maximum scour depth and assumes that the physical property of the subsoil remains unchanged. However, this method ignores the effect of the scouring hole size and the stress history around the foundation, leading to high redundancy of the pile length. The authors consider the effect of the size, and deduce the theoretical equation for the lateral bearing capacity of single pile based on the modified p-y curves and the study by Reese. Then, simulation was carried out using LPILE and the results were compared with those obtained from model tests. The results show that the equivalent scour depth formula derived based on the principle of invariable ultimate soil resistance is reliable, and the relative error between the LPILE calculated value and the test value is 13%-17%, which indicates that the actual situation can be accurately predicted. As the scour depth increases, the lateral bearing capacity of the single pile weakens, the free length of the pile increases, and the maximum pile bending moment increases with increasing depth to the pile bottom. The modified p-y curves consider the beneficial effect of soil above the scour pit, and the relative errors between the calculated value and the test value for maximum lateral bearing capacity, pile top maximum lateral displacement, maximum moment, and pile depth of the maximum moment are 3.6%-6.0%, 13.9%-23.5%, 2.9%-4.4%, and 3.3%-7.7%, respectively. The sensitivity of the scouring depth, scouring slope angle, and scouring width parameters were analyzed to determine their effects on the scouring hole and the validity of the theoretical equation; the results show that the impact of the three parameters decreased in turn, which can provide some reference for engineering design.
  • HU Xiang-dong, HONG Ze-qun
    China Journal of Highway and Transport. 2018, 31(8): 113-121,154.
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    A special circle-pipe freezing model with different pipe spacing based on simplification of the dark excavation section of the Gongbei tunnel in Hong Kong-Zhuhai-Macao Bridge is proposed to provide reference for the design and construction of freeze-sealing pipe roof (FSPR), which is a new underground construction method, considering the special arrangement of two types of freezing pipes ("circular master freezing pipe" and "profiled enhancing freezing pipe") used in active freezing period. In order to obtain the analytical solution of this special model, the circle-pipe model was first converted to row-pipe model with non-equal spacing between adjacent freezing pipes using conformal mapping method. Then, two simple single-row pipe models with equal spacing were superposed to obtain the analytical solution of this row-pipe model according to the separability of boundary conditions for Laplace equations. The analytical solution of the circle-pipe model was then determined by the corresponding law of parameters in conformal mapping. Three characteristic sections in a periodic unit of this special freezing model were analyzed, and the correctness of the analytical solution was verified by comparing the results with the numerical simulation results calculated using ANSYS software. The freezing effect of FSPR in the Gongbei tunnel was also analyzed and visual display with temperature cloud figures was implemented based on the analytical solution. The results show that the temperature of all characteristic sections can be frozen to a sufficiently low negative value, which is far below the soil freezing temperature, and the sealing effect of FSPR between two adjacent jacking pipes can be fully guaranteed. Intersection 1 passes through the middle of two adjacent jacking pipes, so the temperature on this section is slightly higher than that on the main section and can be lower than -15℃; this value also decreases with the offset angle of the freezing pipes. Besides, the maximum temperature difference occurs on the axis section and decreases gradually with the freezing process. Meanwhile, the temperature distribution in the frozen soil curtain also shows a tendency toward stabilization.
  • YU Jian-han, LI Ming-shui, LI Shao-peng, LIAO Hai-li
    China Journal of Highway and Transport. 2018, 31(8): 122-128.
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    The reduction of the wind direction to the basic wind speed and topographic effect on the design wind speed of bridge in mountainous area are investigated by taking a long-span bridge crossing a deep valley as a case study. The wind field of the bridge site is numerically calculated using the joint distribution function of the wind speed and wind direction and computational fluid dynamics software, FLUENT. First, the relationship between the monthly extreme value distribution and the annual extreme value distribution is obtained using the wind speed data of a weather station near the bridge and adopting the extreme-value type Ⅰ method when the wind speed observation data is insufficient such that the 100-year basic wind speed without considering the influence of wind direction is calculated. Second, by using the joint distribution function of the wind speed and wind direction, the 100-year basic wind speed considering the effect of wind direction is calculated to investigate the reduction effect of the joint distribution of wind speed and wind direction on the basic wind speed. FLUENT software is applied to simulate the wind field in the bridge area under the two conditions above and the maximum wind speed, namely the design wind speed, is obtained under different wind directions. The results show that the joint distribution of wind speed and wind direction and the topographic effect affect the design wind speed. If the joint distribution of wind speed and wind direction is not considered, the design wind speed will be conservative when the wind direction of the local maximum basic wind speed is different from the wind direction of the maximum terrain amplification effect. Finally, an analysis framework for determining the bridge design wind speed is proposed using the research results. This method is more reasonable and better suited for engineering applicability, and it provides a reference for the determination of the bridge design wind speed in a mountainous area.
  • ZHANG Yuan-zhu, JIN Li-qiao, WEI Xin-jiang, SHI Hong-gang, XU Kui-xin
    China Journal of Highway and Transport. 2018, 31(8): 129-136.
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    To study the water transport process and influencing factors on the cracked concrete in underwater tunnels, a motion equation in cracked unsaturated concrete under external water pressure was proposed based on the Richards equation and cubic law. Penetration experiments with cooling pressure water on the internal holes and cracks of concrete were designed according to the service environment, namely, the wall side of the underwater tunnel bearing external water pressure, and the contacting atmosphere. Infrared thermography was used to visually study the water infiltration process in cracked concrete. The influence of the geometrical fracture characteristics, external water pressure, and initial saturation on the water transport in cracked concrete was analyzed based on the infrared radiation characteristics. Meanwhile, the test results and the influencing factors in the equation of water motion were compared. The results show that, the greater the water pressure, or the lower the initial saturation of concrete, the greater the temperature difference is between the inside and outside of the cracked concrete test block, and the steeper the change in the surface temperature curve, which indicates that the water velocity is correspondingly faster and the penetration depth is greater. As a result, it was verified that the external water pressure and initial saturation are both driving factors in the water transport in cracked concrete. The greater the crack width or the longer the crack length, the lower the infrared temperature of the concrete block surface is, and the greater the temperature difference between the inside and outside of the test block, which demonstrates that a greater crack area results in a greater infiltration flow of cooling water and a greater penetration depth, thereby proving the positive correlation between the crack width and permeability of cracked concrete. In addition, the observed effect of an infrared heat map from the direction of the vertical fracture is more obvious than that from the direction of a parallel fracture. When predicting the leakage of an underwater tunnel, it is suggested that the geometric characteristics of the crack, the external water pressure, and the initial saturation not be neglected; otherwise, the water velocity and flow will be underestimated, which will affect the long-term safety and durability analysis of underwater tunnels.
  • REN Rui, LI Jie, WANG Ya-qiong
    China Journal of Highway and Transport. 2018, 31(8): 137-144.
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    To study the local resistance loss of a tunnel ventilation system, a numerical simulation model was developed for the 90° bend of the air duct of the ventilation system. The standard k-ε turbulence model was used for the computational fluid dynamic (CFD) analysis to simulate the airflow in the duct with the 90° bend. The local resistance loss of the 90° bend (ζ90°) and the velocity field were analyzed under conditions of varying dimension parameters (r/D). After setting the number of guide plates to investigate the effect of different drag reduction measures, a model test of the 90° bend of the air duct was conducted, and the reliability of the numerical simulation model was validated by analyzing the correlation result between the CFD model and field measurement. The results show that by increasing the radius of the inner wall of the bent duct and by setting guide plates in the 90° bend, the vortex formed by the rapid changes in the flow direction in the 90° bend and the local resistance loss coefficient can be effectively reduced. However, the guide plates occupy a part of the flow space in the duct and exhibit a diversion effect as well as resistance effect simultaneously. Therefore, when the value of r/D is small, the ζ90° reduces first and then increases with increasing number of guide plates. When the value of r/D is relatively high, the resistance effect of the guide plates is greater than the diversion effect, and the value of ζ90° increases with increasing number of guide plates. In the numerical simulation model, when the value of r/D is 0.2 and 0.3, the number of guide plates with the least resistance loss is 2 and 1, respectively; when the value of r/D is 0.4, 0.5, and 0.6, the resistance loss is the least with no guide plates.
  • XU Jian-min, YAN Xiao-wen, MA Ying-ying, WANG Yu-jun
    China Journal of Highway and Transport. 2018, 31(8): 145-154.
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    Previous studies have focused mostly on static passenger car equivalent (PCE) and showed that static PCE cannot accurately describe the interaction among vehicles in a crowded state. They did not consider the influence of the dynamic interaction among vehicles in different traffic states. To estimate the PCE according to the traffic state of a network dynamically, this study employed a macroscopic fundamental diagram (MFD) to analyze its sensitivity to the proportion of heavy goods vehicles (HGVs) on roads based on the checkerboard road network. This study also proposed a method to calculate the PCE of HGVs under various traffic states. First, the road network simulation model was constructed and the MFD was defined and verified using microscopic simulation. Secondly, the MFD of the network was modeled using a piecewise linear function according to simulation data, and multi-group simulation experiments were designed with changes in the proportion of large cars. Changes in the MFD shape along with various proportions of HGVs were studied. The sensitivity of the MFD to HGV proportion was analyzed qualitatively and quantitatively. Third, a method to estimate the PCE of HGVs under different typical traffic states based on the MFD was presented. The proposed PCE formulation indicates that the PCEs of HGVs are related to the proportion of HGVs under uncongested conditions, which corresponds to the rising section and continuous section of the MFD curve. When it is related to the number of vehicles in the network (or density) under congestion, it corresponds to the falling section. The method and insights proposed in this paper provide an understanding of HGV influence on the network traffic state, as well as provide support to transport planning and operation.
  • ZHAO Huai-xin, DENG Ran-ran, ZHANG Ying-jie, DING Ming-hang, SUN Zhao-yun, LI Wei
    China Journal of Highway and Transport. 2018, 31(8): 155-164.
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    To analyze expressway traffic situations more effectively, a data-mining method that can be used to analyze expressway traffic conditions by using the data of expressway mass data collection is proposed. First, the data of the specified entering station and leaving station were selected, and some fields were deleted from the vast number of Guizhou expressway fee data, so that only the data related to this study were retained. The time of driving into the entering station and driving out of the leaving station was used to calculate the vehicles' staying time between the two toll stations, and the transit time was added to the original data. Then, the outlier detection algorithm was used to clean the data and to reject outliers. Clustering by fast search and find of density peaks was used to perform cluster analysis on driving duration after completing the above pretreatment process. The distance between each piece of data was first calculated, and then the distance matrix was used as the input of the algorithm, and the clustering result was exported. The clustering effects of the algorithm used and of the K-means algorithm on the driving duration were compared. The clustering result of the proposed algorithm was closer to the actual situation. Then, the fee data for the fourth week in February and the Spring Festival were clustered separately. Comparing the results shows that the proportion of traffic in each model during the holiday season changed. The average transit time of different models at different time periods was analyzed by combining the above results. The results show that the method used can effectively classify vehicles passing through a certain expressway, and the classification result is consistent with the traffic condition of the vehicles on the expressway during real operation. This method can provide a scientific basis and data support for expressway operation management and maintenance directions.
  • LYU Neng-chao, CAO Yue, QIN Ling, WU Chao-zhong
    China Journal of Highway and Transport. 2018, 31(8): 165-172.
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    Excessive driving workload is the leading contributing factor to driving performance impairment and traffic crashes. Therefore, establishing a controlled workload environment is significant for driving behavior and traffic safety studies. This study aims to evaluate traffic safety by analyzing the cognitive workload of drivers during driving behavior and prove the effectiveness of traffic sign information volume on workload. The driving workload of drivers was tested based on traffic signs with different information volumes. 44 subjects were recruited to conduct a traffic sign cognition experiment under a static controlled cognition environment. The traffic sign information volume was quantified by using information theory. Different complex traffic signs were used for loading cognitive workload. Subjective workload assessment and recognition time of subjects for every traffic sign were collected. The results reveal that workload is highly related to the volume of information on traffic signs, and reaction time increases with information volume, while the driver's gender and driving experience have no significant effect on the reaction time and the subjective driving workload quantification. This shows that the cognitive workload of the subsequent driving experiment can be controlled by the information volume on traffic signs, with no difference due to gender and driving experience. The research results can be used to evaluate traffic safety by involving a secondary task of driving, which better considers the drivers' cognitive characteristics.
  • GUO Zi-zheng, LIU Xian, CHEN Rui-ya, PAN Yu-fan, SHI Lei, ZHANG Jun
    China Journal of Highway and Transport. 2018, 31(8): 173-180.
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    To investigate the influence of fatigue on drivers' action monitoring ability, a dual-task experiment that combined simulated driving with a Go/NoGo task was adopted. The event-related potential (ERP) technique was adopted to analyze the correlations between the EEG index (ERN amplitude) that reflected action monitoring ability and the driving behavior indexes (SDLP, SRR, SDS) of 30 drivers to validate the characterization effectiveness of the driving behavior indexes. The diversities of the ERN amplitude, SDLP, SRR, and SDS between the stage one (0-15 min) and stage two (75-90 min) were analyzed to investigate the influence mechanism of fatigue on action monitoring ability. The results showed that the ERN amplitude had a connection to the SDLP, SRR, and SDS indexes. Compared with stage one (0-15 min), the SDLP, SRR, and SDS indexes increased, and the ERN in the frontal central area decreased significantly in stage two (75-90 min). The results indicate that fatigue impairs the function of action monitoring of drivers, which is regulated by prefrontal lobe. In addition, the correlation analysis indicates that the SDLP, SRR, and SDS indexes can be used as driving behavior indexes that measure action monitoring ability.
  • WANG Lei, HUA Jun, YANG Yun-feng, LIU Hao-xue, ZHU Tong
    China Journal of Highway and Transport. 2018, 31(8): 181-188,196.
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    The management of road dangerous cargo transportation is an important content of road transportation management. To study the interaction between supply and demand of all kinds of dangerous cargo and social economy development, based on system dynamics theory, this paper firstly determined the boundary of road transportation system of dangerous cargo, and divided the system into subsystems of capacity and demand and introduced the supply and demand coefficient of dangerous cargo. The causality diagram was set up to explore the positive and negative feedback relations between the various factors. Secondly, the supply and demand coefficient of dangerous cargo was introduced to establish the flow diagram. By establishing the main variable equations, the linear relation and nonlinear relation between the factors in the system were expressed. The model was tested, including authenticity test and sensitivity analysis. Finally, the initial values were set. The model was set up to study the feasible strategies of making the behavior patterns of supply and demand coefficient stable. Taking gas transportation in Huizhou City, Guangdong Province as an example, the main factors affecting the coefficient were analyzed to simulate the model. 7 policy scenarios were set up, and the software named VENSIM was used for simulation The results show that increasing the utilization degree and transportation efficiency of vehicles can effectively improve the coefficient. Increasing the tonnage of transport vehicles and adjusting the capacity structure of dangerous cargo can improve the situation on supply and demand and increase the coefficient. After increasing capacity, the behavior pattern of supply and demand coefficient tends to be stable. Comprehensive regulation is better to improve the performance of the behavior pattern of supply and demand coefficient. The model can effectively simulate the management control strategy and provide support for the improvement and improvement of road transportation management department.
  • GUO Ying-shi, JIANG Zheng-min, BAI Yan, TANG Jie-zhen
    China Journal of Highway and Transport. 2018, 31(8): 189-196.
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    Autonomous vehicle path tracking has an important role in the motion control of unmanned vehicles. Presently, commonly used path tracking models consider path tracking precision as the main control goal, and largely ignore the unmanned vehicle ride comfort and humanoid level. To investigate the anthropomorphic degrees of unmanned vehicle path tracking control methods, and to improve ride comfort, four typical path tracking models were established based on the steering geometry, vehicle kinematics, and dynamics theories. The humanoid level and ride comfort of different path tracking methods were characterized by the maximum lateral acceleration aymax and the sum of squares of the steering wheel angles (δw2) during path tracking. A polynomial lane change path was established based on the actual experimental vehicle data. Additionally, a CarSim/Simulink co-simulation model was established. The results of lane changing under different vehicle speeds revealed that the tracking error of the above models increased with the increase of vehicle speed, and satisfactory path tracking results were achieved. The steering geometry method with preview and optimal dynamic control with feed forward term path tracking models had a good humanoid level degree. The ride comfort of the kinematics path tracking model was the least satisfactory with aymax being over 0.7 m·s-2 and δw2>2.7×103 being under 100 km·h-1. The steering geometry path tracking model without preview had the highest tracking accuracy and highest degree of humanoid level, with a maximum lateral acceleration below 0.5 m·s-2 under 120 km·h-1.
  • YANG Ze-yu, DENG Qian-wang, HU Man-jiang, ZHOU Hua-jian, ZHONG Zhi-hua
    China Journal of Highway and Transport. 2018, 31(8): 197-204.
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    In this study, to reduce the interference of gravity and the fixture locating error in the location accuracy of sheet metal components, and to improve the robustness of the locating scheme during the welding clamping process, the locator layout in the first datum plane of sheet metal components was optimized on the basis of finite element analysis. The influence coefficient analysis method was introduced to establish the evaluation index of a locating scheme that could reflect the sensitivity of the location accuracy to the fixture locating error. A multi-objective optimization model was created based on the trace of the influence coefficient square matrix and the effect of gravity on the location accuracy. The Kriging surrogate model was adopted to establish an objective function. To improve the prediction accuracy of the surrogate model, the sequential Kriging-GA method was proposed. By combining the optimal point principle with the expectation improvement criterion, new samples were repeatedly added to the interest-domain in order to update the surrogate model. This improved the prediction accuracy and ensured a global search ability. The results of the optimization examples revealed that the sequence Kriging model had a high prediction accuracy, and the prediction error in the interest-domain could be lowered to 1%. In comparison with the GA, the proposed method could reduce the simulation workload by 75% and greatly improve the design efficiency. Under different locating error combinations, both the mean and variance of the key point deformations decreased significantly, which implies that the sensitivity of the location accuracy to the fixture locating error was reduced, and that the optimized locating scheme had strong robustness.
  • YU Man, ZHOU Chen-yu, WEI Lang, ZHAO Xuan, YU Qiang
    China Journal of Highway and Transport. 2018, 31(8): 205-217.
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    To reduce the output force of active actuator and improve the robustness of a control system, an H-outer-loop controller was built based on a 7-degree-of-freedom full car model of the Takagi-Sugeno (T-S) fuzzy modeling technique to adapt its strategy to different road disturbances and improve system efficiency. The resulting optimizing problem was transformed into a solution issue of linear matrix inequalities associated with system stability analysis, suspension stroke limit, and force constraints. By integrating these via parallel distributed compensation method, the controller gain was obtained. In response to the uncertain parameters, the adaptive robust control was employed in the inner loop to improve the force-tracking performance. Based on the simulation test under the condition of different road profiles, cross-axle double-road input, and control force tracking, the suspension performance indexes were analyzed and the control force was compared to backstepping and optimal control. The results show that the T-S fuzzy model based on the H control can reduce the root mean square (RMS) value of acceleration by more than 80% and 47% compared to passive suspension and optimal control, respectively. The RMS value of acceleration increases when under intensive disturbance with suspension dynamic deflection suppression. In cross-axle double-road input tests, the mean values of mass, pitch, and roll accelerations were reduced by more than 55%, 83%, and 90%, respectively, compared to those of passive suspension under a small road disturbance. The peak control force was observed to reduce by more than 20% than that of the backstepping control and optimal control method, and the tracking accuracy was improved. These results show that the combination of the H control and adaptive robust control based on the T-S fuzzy model can reduce the system energy consumption with a guaranteed suspension performance.
  • ZHANG Chen-guang, XIE Li-yang, JIAO Sheng-jie, GU Hai-rong
    China Journal of Highway and Transport. 2018, 31(8): 218-226.
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    To study the influence of the deflector position on the flow field and particle diameter for volute separators and provide guidance on the practical use of recycled dust in asphalt mixing plants, numerical simulations and verification experiments were conducted for the flow field of gas and gas-solid phases at three deflector positions. By using FLUENT software as the platform, a Reynolds stress model and the coupled interphase discrete particles model were used to simulate the flow fields of the gas and gas-solid phases, respectively. In the gas-solid phase simulation, the trajectories of 16 400 dust particles with diameters of 50 to 1 000 μm were tracked, and the removal efficiency of dust was calculated. The recycled dust was collected at three deflector positions in the asphalt mixing plant site. The size distribution of dust particles was evaluated via sieving and electron microscope scanning; the results were used to verify the conclusions of the numerical simulation. The research findings are as follows:when the deflector is at the O position, the axial symmetry for radial velocity, axial velocity, and static pressure are better than those for the W and M positions. Additionally, the asymmetrical turbulence and entrainment swirl can be effectively restrained, and the swinging phenomenon of vortex core can be weakened. Furthermore, collisions and rebounding may cause the trajectory of dust particles to differ according to the position of the deflector. This process can affect the removal efficiency of different sized dust particles. When the deflector is at the O position, the dust with the diameter larger than 100 μm can be more effectively collected. In addition, under the O position condition, the average particle diameter of the recycled dust is 117.6 μm and that of the dust in the last sieve is 49.9 μm. These two diameters are greater than those observed under the W and M position conditions. The experimental results are consistent with those of the numerical simulations. In the actual production process of asphalt mixing plants, the deflector of the volute separators should initially be placed at the O position. Additionally, the deflector position should be adjusted according to the actual requirements related to the size of the recycled dust particles.