Journal of Highway and Transportation Research and Development (English Edition)

To study the effect of iron tailings content on the workability, mechanical properties, and durability of road concrete, different proportions of iron tailings were used to replace natural sand as fine aggregate to prepare road concrete. The workability, compressive strength, flexural tensile strength, splitting tensile strength, dry shrinkage, impermeability, and wear resistance of concrete were tested. The results showed that the workability of concrete mixed with iron tailings was good, which could fully meet the construction requirements. The 28-d flexural tensile strength of iron tailings concrete exceeds the designed standard value of 4.0 MPa, and the maximum is 5.9 MPa. With the increase of the dosage of iron tailing sand, the dry shrinkage strain, and wear amount of concrete gradually increased and the water penetration depth decreased. The introduction of iron tailings will improve the impermeability and wear resistance of concrete, but it will increase the dry shrinkage. Therefore, the content of iron tail sand should not be too large. Under the condition of ensuring the performance of concrete, the content of iron tailings in fine aggregates should be controlled at about 50%.

In order to accurately evaluate the durability of stay cables of parallel steel wire bundles for bridges, the study is conducted on fretting wear during service. First, based on the structure of the parallel steel wire rope, the squeezing forces between the steel wires at different positions caused by the twisting angle and the sheath clamping effect are calculated separately. Then, a contact mechanics model between parallel steel wires is established, and a calculation method for the depth of fretting wear of parallel steel wires is proposed based on the amplitude and frequency of fretting. Finally, the wear depth of parallel steel wire cables in a cable-stayed bridge that has been in service for 20 years is calculated and compared with the measured results. The result shows that (1) the contact mechanics model can accurately calculate the wear depth of wires at different positions of parallel wire rope during service; (2) in the length direction of the cable, the wear degree of the steel wire near the end is greater than that of the middle steel wire, from the section distribution of the cable, the wear degree of the outer steel wire is light, the wear of the steel wire near the center of the circle is serious, and the theoretical calculation results are basically consistent with the detection results of the old cable of the real bridge; (3) the development of steel wire wear depth shows a power function rule of first fast and then slow with the increase of time, the wear rate increases with the increase of contact force between steel wires, vibration frequency and amplitude of cable; (4) the zinc coating of steel wire in the example will be worn out in 4. 5 to 9 years, which is far lower than the failure time of zinc coating caused by environmental corrosion. Fretting wear will lead to premature failure of zinc coating and shorten the initiation time of fatigue crack. If fretting wear between parallel steel wires is not considered, the life evaluation of cable will be unsafe.

In order to improve the performance of the bridge deck pavement structure, improve the stress state of the bridge deck pavement structure layer, reduce the disease of old concrete bridge asphalt pavement, grasp the stress state of the bridge deck pavement structure layer and material performance, the asphalt pavement material and pavement structure are optimized. Based on the finite element analysis method, the finite element model of asphalt pavement on cement concrete bridge deck is established. The interlaminar shear stress, interlaminar tensile stress, and surface shear stress are selected as the main mechanical control indicators, and the stress variation rule of different thickness and modulus of pavement layer under traffic load is analyzed. The result shows that (1) shear failure is the main failure form of asphalt pavement on bridge deck, and the thickness of asphalt pavement is the main factor affecting the stress distribution inside the pavement, while the modulus of asphalt pavement material has a little effect on the stress distribution. The proper thickness of asphalt pavement can improve the distribution of internal stress, therefore, two kinds of bridge deck pavement structure design schemes, SMA composite structure and AC composite structure are proposed. (2) Based on the indoor test, the high-temperature stability, low-temperature crack resistance, water stability and water permeability of SMA-10, SMA-13 and Ac-13 asphalt mixtures are studied, it is known that all performance indicators of the three asphalt mixtures meet the requirements of the design code, but each has its own advantages and disadvantages in different performance. (3) Finally, according to the results of the performance test and the principle of optimizing the material of the bridge deck pavement, under the condition that the performance can meet the requirements of the project, combined with the requirements of the project cost economy and the safety of the bridge structure, a composite structure is recommended as the old concrete bridge deck pavement structure, AC-13 is selected as the old concrete bridge deck pavement upper and lower layer pavement material.

In order to improve the engineering quality of highway tunnels, accelerate the construction speed, reduce the material consumption and construction cost, and improve the construction environment, this study proposed an optimized precast inverted arch form. ABAQUS was used to establish the three-dimensional finite element model of the precast inverted arch reinforced concrete structure. Considering the influence of different strength grades of bolts, bolt preload, bearing load, and steel bars, the mechanical properties of the optimized precast inverted arch structure joints of highway tunnel were analyzed. The results show that the bolt prestress can effectively increase the capacity of the joint to bear positive bending moment. Under a large load, the higher the bolt grade, the greater the maximum stress and the smaller the maximum strain; under this precast inverted arch structure, the vulnerable parts of the lower bolt are the connection between the screw and the nut, the vulnerable parts of the upper bolt are the screw, and the vulnerable parts of the concrete joint are the joint and the structural corner. The results have guiding significance for ensuring the safe construction of new prefabricated inverted arches of highway tunnels.

In order to select the barrier level for roadside safety design, models of single unit truck collisions with Level 3 to Level 6 concrete barriers were established by adopting explicit finite element software LS-DYNA 3D; the impact speed was between $40\mathrm{km}/\mathrm{h}$ and $80\mathrm{km}/\mathrm{h}$. A finite element model of a modified vehicle verified by full-scale impact test to improve credibility of the simulation model was used. The relations between impact speed, level of concrete barriers, and the amount of vehicle overhang beyond the barrier was studied, the effectiveness of concrete barriers shielding roadside obstacles was quantitatively evaluated, and the minimum safe distance from the traffic side of barriers to roadside obstacles was obtained. The relationship between the Chinese specification method and the 50 ms mean lateral impact force in the calculation of barrier impact force is compared. The equation of important roadside obstacle impact force was developed and evaluated, and the design value of important roadside obstacle impact force is revised. The results indicate that when the barrier level is Level 3 to 6 and the design speed is $60\mathrm{km}/\mathrm{h}$ for roads, the minimum safe distance between barriers and roadside obstacles is 1.8 m to 1.2 m, and for roads with the design speed of $80\mathrm{km}/\mathrm{h}$, the minimum safety distance between barriers and roadside obstacles is 3.0 m to 1.7 m. The single unit truck VI_n of enhanced barrier is at least 5% lower than the F-shape barrier. The enhanced barrier contains and redirects the single unit truck in a more stable manner. The 50 ms mean lateral impact force between the cargo and the barrier is close to the Chinese specification method. Under the same impact conditions, a higher level of barrier lowers VI_n significantly, however, the impact force of the barrier increases greatly since the cargo is more likely to collide with barrier.

Model calibration ensures the reliability of traffic simulation models for designing and evaluating traffic management schemes. This paper introduces a metamodel-based method for calibrating a microscopic simulation model developed with Vissim. Initially, a Vissim simulation was devised for an expressway merging zone. A parameter sensitivity analysis was conducted using a backpropagation neural network (BPNN). Several key parameters of the Vissim model were identified based on sensitivity indices. A metamodel called the Kriging model was created to show how Vissim parameter inputs affect simulation outputs. Based on the metamodel, the differential evolution (DE) algorithm was applied to find the best parameters for the VISSIM mode. The average travel time simulation of the calibrated Vissim model deviated from field survey data by less than 3%. The statistical analyses affirm the efficacy of the Kriging-DE calibration method. The metamodel-based method offers a promising tool for model calibration in traffic management.

To study the operation regular pattern of the road freight market and quantitatively describe the fluctuation of the road freight market, based on the statistical data of the road freight industry and the dynamic operation data of freight vehicles, this paper adopts the prosperity index method to select indicators closely related to road freight from the dimensions of market scale, transportation efficiency, transportation price and macro environment, and to establish the road freight market prosperity index system. Meanwhile, the indicators are divided into three categories: advance, synchronization, and lag by time difference correlation analysis. The monthly index of road freight market is synthesized according to the prosperity index model. Through the synthetic calculation and statistical analysis of the monthly data of road freight transportation from 2018 to 2020, combined with the actual operation of the industry, the index fluctuation threshold is studied and determined to form an early warning signal light for the road freight market to visually describe the fluctuation of the road freight market. The result shows that: road freight market has strong correlation with macroeconomic operation, showing obvious seasonal change characteristics as a whole. Meanwhile, it also shows strong elasticity and toughness. During the COVID-19, the road freight industry recovered rapidly in the shape of “V”, which recovered to the normal level before the secondary and tertiary industries, fully reflecting the basic and leading role of the industry in serving economic and social development.

In view of the complexity of the bulk cargo transportation demand forecast, a forecast method for bulk cargo transportation demand based on the production and transportation coefficient is put forward. The route of transport structure adjustment is determined according to the development trend of bulk cargo transport demand. Taking Heilongjiang province as an example, taking into account factors such as the amount of chemical fertilizer applied, rural electricity consumption, total power of agricultural machinery and the area sown for grain crops, the GM(1,1) model and the GM(1,1)-MLP neural network model are established to forecast grain yield, and are verified by actual data. Heilongjiang’s grain production and transportation coefficient are determined based on statistics on Heilongjiang’s permanent population, urbanization rate of the permanent population, food production, per capita food consumption of urban and rural populations. The grain transport volume for the next few years is forecast combining with the forecast of grain output and the production and transportation coefficient to analyze the trend of grain transport demand in Heilongjiang and provide a basis for formulating the structural adjustment plan for bulk cargo transport in Heilongjiang. The result shows that (1) compared with the GM(1,1) model, the precision of the GM(1,1)-MLP neural network model is improved by 1.68%; and (2) based on the forecast results, the demand for grain transport in Heilongjiang will continue to increase, and the transport demand will continue to increase. Heilongjiang is still the main part of the bulk cargo transport object, actively adjusting the grain transport structure, promoting the shift of medium and long-distance grain transport to railway transport, and road transport as a short-barge distribution at both ends of railway transport, combined rail and public transport plays an important role in optimizing Heilongjiang’s bulk cargo transport structure.