Abstract:In order to study the transmission and distribution of contact force chain in asphalt mixture under different stress modes of tension, compression, bending and shearing, clear different aggregate mortar components resistance load in the respective levels of contribution, based on industrial computed tomography (CT) and digital image processing method for aggregate particle model, using software PFC3D constructed SMA13 gradation of asphalt mixture of 3D digital specimen, and virtual tests were carried out under different stress modes. The transfer and distribution characteristics of contact force chain inside asphalt mixture and the distribution of contact force composition of different components of mortar aggregate were visualized and quantitatively analyzed. At the same time, the force chain probability was used as a quantitative index to analyze the distribution characteristics of various contact force chains under different force modes. The results show that the three-dimensional digital model established by discrete element method can better simulate the low temperature mechanical behavior of asphalt mixture. In uniaxial compression mode, the ratio of all kinds of contact strong chains is the highest among the four stress modes. The interlocking extrusion between aggregates is the main factor to resist external load, and the contact force level transmitted by aggregates accounts for 69.9% of the total contact force. Under indirect tensile and semi-circular flexural loading modes, the proportion of the strong chain between the interior and interface of asphalt mortar is significantly higher than that between aggregate. The contact force transmitted by asphalt mortar accounts for 50.1% and 57.4% of the total contact force, respectively. The bond between asphalt mortar is the dominant factor to resist damage. In uniaxial penetration force mode, the proportion of strong chain between asphalt mortar and interface is slightly higher than that between aggregate, and the contact force transmitted by aggregate accounts for 64.7% of the total contact force. The ratio of strong and weak force chain can better reflect the load transfer capacity of different components of asphalt mixture under different stress modes. The results can provide theoretical basis for understanding the mechanical behavior of asphalt mixture from the perspective of meso-structure.

Abstract:There are multiple choices in the design of the target mix proportion and gradation composition of asphalt mixtures, and there is a problem of how to obtain the optimal gradation, which is related to the quality of mix proportion design and directly affects the pavement quality and service life of the pavement. Therefore, a scientific method is needed for gradation optimization. Based on the optimization theory, analyze the characteristics of mixed material performance indicators, and construct a three-level optimization index system consisting of non quantitative indicators, conventional quantitative indicators, and road performance indicators. Design three sets of typical gradation, conduct typical performance tests and analysis, and obtain the values of each evaluation index. Using Delphi expert survey method for membership degree, blind degree analysis, and overall understanding index weighting. Using grayscale model theory, the evaluation indicators are normalized, and the correlation degree of each indicator is analyzed. The grayscale model system is comprehensively evaluated and ranked step by step, and the optimal target mix ratio grading is ultimately selected based on the ranking results. In the study, the indicator system and process of the grayscale model analysis method were proposed, and the influence of the resolution coefficient values in the method on the optimization results was discussed. Research has shown that this method can systematically and comprehensively analyze the performance index system corresponding to the gradation composition, screen out the optimal characteristics that meet the road performance indicators, and provide an effective technical approach for the gradation optimization of asphalt mixture target mix design.

Abstract:In order to achieve an objective and fair evaluation of the integrity quality of cement-treated aggregate base layers(CTAB), eliminate the randomness of quality evaluation of 7 d core samples, and make up for the limitations of construction quality evaluation due to the lack of consideration of climatic characteristics and highway grade, five highways, including expressway, primary, secondary and third-grade roads are selected, a large number of core tests are carried out on CTAB at 7 d age, and the condition of cores are systematically investigated, statistically analyzed, according to the influence on pavement structural performance, cores category and grade are classified. According to the integrity degree of the core, it can be divided into three categories: integral class, incomplete class and loose class, the difference in the integrity of the core represents the difference in its diffusion load stress capacity, based on the density, the cores are further divided into eight grades, the difference in core density reflects the difference in using function, the calculation method of core integrity rate is proposed, and the principle of determining the technical standard of core integrity rate is determined, F(Ⅰ+Ⅱ) should be used as the evaluation index for seasonal frozen area, and F(Ⅰ) should be used as the evaluation index for non-seasonal frozen area. according to the regression curve, the technical standard of core integrity rate for different grades of roads in different areas within 7 days is proposed. The results show that the core integrity rate and road grade showed a linear trend, and the influence range of road grade is 2%-9%, the influence range of coring-mode is about 10%, and the influence range of climate is about 5%. The research results achieve the quantitative evaluation of cores quality and integrity properties of semi-rigid base.

Abstract:Tunnel excavation in fractured rock masses will induce a strongly hydro-mechanical coupling effect, which may cause significant rock mass damage and water pressure perturbation. This paper establishes a hydro-mechanical model to analyze the rock damage and fracture deformation induced by the tunnel excavation and the sequential drainage phase in fractured rocks. Afterwards, the model is used to investigate the effect of fracture networks on the excavation-induced damage in different fracture networks. It was found that the proposed model can effectively simulate the tunnel excavation and drainage phases in rocks embedded with discrete fracture networks. The damage evolution, fracture deformation, and groundwater seepage were well-captured in the simulation. The fracture network was found to significantly affect the uniformity of stress distribution. The coupling effect of tunnel excavation and groundwater seepage caused high stress zones around the tunnel, and there was a significant correlation between local stress, fracture deformation and water pressure. The distribution characteristics of fracture networks played a leading role on the development of excavation-induced damage, which further influenced the formation and development of excavation disturbed zone and excavation damaged zone.

Abstract:In order to clarify the influence of crack characteristics on the bearing capacity of lining structures under loose load, the stress and deformation characteristics, failure modes and ultimate bearing capacity of structures with cracks were studied by 1∶10 model test and numerical analysis. The results show that: For specimens with prefabricated crack length less than L/3 (longitudinal length of specimen) and depth less than 0.7H (thickness of the specimen), the fracture development process is characterized by stages. The failure of specimens is caused by the failure of the vault and belongs to ductile failure. For the specimens with prefabricated crack length no less than 2L/3 or depth no less than 0.9H, there is no stage characteristics in the crack development process, and the failure of the specimens is caused by the failure of the vault, which belongs to the brittle failure. With the increase of crack length and depth, the structural ultimate bearing capacity decreases. When the length of prefabricated crack is L/3 and the depth is 0.3H, 0.7H, 0.9H, and when the length is 2L/3 and the depth is 0.3H, 0.7H, the ultimate bearing capacity of the specimen is 86.96%, 78.26%, 73.91%, 69.57%, 60.87% of the complete specimen. Compared with the crack depth, the length has more obvious effect on the mechanical properties of the structure, and can be taken as an important index of fracture evaluation. A formula for calculating the bearing capacity of the lining based on the characteristics of cracks is proposed, which can be used to determine the ultimate bearing capacity of the lining with cracks, and provide a basis for the evaluation of structural performance, the selection of reinforcement timing and reinforcement parameters.

Abstract:In order to improve the strength of sludge, solve the problem of dredging sludge treatment in an environmentally friendly and efficient manner, biological enzymes combined with cement are used to solidify the sludge. Through the unconfined compressive strength test and direct shear test, the influence of biological enzymes on the strength of cement solidified sludge were preliminarily analyzed. The synergistic solidification mechanism was further explored by means of cation exchange capacity test (CEC),scanning electron microscope test (SEM), X-ray diffraction test (XRD), and infrared spectroscopy (FTIR). The results show that the combination of biological enzymes and cement solidification treatment has a significant improvement effect on the strength of sludge, with a maximum strength increase of 73.8%.Moreover, the amount, type and curing time of biological enzymes influenced its solidification effect, but biological enzymes do not react chemically with minerals in the soil. The combined solidification action of biological enzymes and cement is mainly achieved by promoting cation exchange in the sludge, reducing the electromotive potential of soil, improving the cementation of cement hydration products, promoting the cementation of active clay minerals, and catalytically forming the coating structure. Among all kinds of biological enzymes, Louis enzyme has the best curing effect. The unconfined compressive strength of Louis enzyme cement solidified sludge in 7 days can reach 378.8 kPa, and the cohesion and angle of internal friction can reach 307 kPa and 52.3°, which are increased to 73.8%,33.2% and 55.2% respectively higher than cement solidified sludge.

Abstract:To strengthen the management and control of the source of risk for road transport of hazardous materials, this paper takes the trajectory data of hazardous materials transport vehicles as the analysis object, and studies the problem of optimal selection of road transport routes which is safe, economical and in line with the preference of enterprises, a context-aware, preference-based personalized route recommendation method for road transport of hazardous materials is proposed. Firstly, the historical trajectory data of hazardous materials transport vehicles is processed, and the route preferences of enterprises are learned by extracting route safe and economical features. On this basis, considering the distance and direction similarity between preference vectors, an improved K-means clustering algorithm (DDM-K-means) is proposed to obtain the categories of route preference. Secondly, according to the time, weather, and distance of the transportation tasks, the route context vectors are established. Rock clustering algorithm is used to classify the categories of route context, combined with the categories of route preference to form the categories of route. Finally, based on neural collaborative filtering, an optimal route selection algorithm (NCF-ORS) is proposed, and the preference ranking of hazardous materials road transport enterprises for route categories is obtained to recommend the optimal route for enterprises. Comparing our method with the baseline algorithms, the results showed that the personalized route recommendation method proposed in this paper had a lower mean absolute percentage error. Therefore, the research in this paper is helpful to mine more potential information from vehicle′s trajectory data, with stronger personalized route recommendation capabilities, and can provide decision support for route selection of hazardous materials road transport enterprises.

Abstract:To alleviate driving fatigue caused by driving on grassland roads, an anti-fatigue warning strategy based on information demand of individual drivers was designed. Based on the questionnaire, drivers were divided into three categories: visual type, auditory type and tactile type. Considering different types of drivers′ customized warning information demand, three kinds of driving fatigue warning strategies on grassland roads were designed, including road warning, vehicle warning and vehicle-road cooperation warning. 21 drivers were selected to carry out driving simulator experiment. The data of KSS scale, subjective evaluation of warning strategy and driving behavior were obtained. The methods of descriptive analysis, statistical analysis and TOPSIS comprehensive evaluation based on entropy weight were applied to test the effectiveness of three driving fatigue warning strategies. The results shown that drivers′ acceptance of the three warning strategies was high; these three warning strategies could alleviate the driving fatigue status in different degrees, the cooperative warning strategy was superior to the other two strategies. Moreover, the alleviation effect of the cooperative warning strategy was more obvious when the driving fatigue degree was deeper. The cooperative driving fatigue warning strategy based on customized information demand of individual drivers was helpful to improve the prevention effect of driving fatigue on grassland roads.

Abstract:The disturbance of straight vehicle trajectories under the interference of right turning vehicles on intersecting roads has become a safety hazard for traffic operation at signalized intersections on urban roads. To improve the ability of direct driving drivers to respond to right-turning vehicles and make correct decisions, it is crucial to reliably predict the disturbance trajectory of direct driving vehicles. This article associated the trajectory distribution characteristics of straight vehicles in different states with the motion information of right-turning vehicles on crossed approach. On the basis of identifying vehicle disturbance trajectories, the time to collision (TTC) was added as the input layer to the model, and a three-layer Gaussian Mixture Module-Input and Output Hidden Markov Model (GMM-IOHMM) was constructed. A method for predicting the disturbance trajectory of through vehicles was proposed, which considers the degree to which right-turning vehicles on the crossed road have an impact on the direct traffic on this surface at signalized intersections. The experimental results showed that the improved model can better fit actual trajectory data during model training compared with traditional HMM, and the fitting effect of GMM-IOHMM has been significantly improved compared with traditional time series models. And TTC is less than or equal to 4.5 s and "yaw angle is greater than 2.35 degrees" can be used as a criterion to determine whether a straight ahead vehicle is disturbed. The trajectory prediction results can more accurately determine the possibility of conflicts between direct vehicles and surrounding vehicles, and can serve as an important basis for the design of assisted driving systems for disturbed direct vehicles and other vehicles traveling together.

Abstract:In order to further explore the internal mechanisms and influencing factors of centrifugal dehydration technology in the treatment of construction waste mud mainly composed of cohesive soil. In this paper, the piecewise linearization method is used to fully consider the non-Darcian flow characteristics in cohesive soil and the nonlinear characteristics of soil deformation. A mud dehydration analysis model that can consider its non-Darcian flow characteristics under centrifugal action is established. The validity of the present model was proved by comparing it with the existing research results and laboratory model test results. On this basis, the influence of the model parameters on the dewatering process was investigated. The numerical results showed that the dewatering rate and the final displacement of the soil-water interface increased with the increase in motor speed. Increasing the initial thickness of mud will increase the final displacement of the soil-water interface but will reduce the initial soil-water interface movement speed. The influence of the compression index on the displacement of the soil-water interface is not obvious in the initial stage, but its increase will lead to an increase in the final displacement of the soil-water interface. The increase in non-Darcian flow parameters will lead to a decrease in soil-water interface displacement, but by increasing the motor speed, the adverse effect of non-Darcian flow on the dewatering effect can be effectively reduced. The research results can provide a reference for the further optimization and application of centrifugal dehydration technology in the treatment of construction waste mud.

Abstract:ln order to make traffic prediction more accurately, aiming at the problems of random assignment and slow convergence of the traditional BP neural network, an improved sparrow search algorithm(SSA) is proposed to optimize the BP neural network prediction model. The model combines the SSA position update principle and the rooster position update method in the chicken optimization algorithm to improve the sparrow search algorithm, which avoids the algorithm from falling into the local optimum and the ineffectiveness of the position update, and at the same time effectively improves the convergence speed of the algorithm. The improved sparrow search algorithm is used to optimize the weights and thresholds of the BP neural network, and the improved SSA-BP neural network prediction model is obtained. The four prediction models, namely, LSTM neural network, BP neural network, SSA-BP neural network and improved SSA-BP neural network, were trained and tested with traffic data, and the prediction results were compared and analyzed in terms of MAE, MAPE, MSE, RMSE and EC. The results show that the BP neural network is better than the LSTM neural network, and the optimized BP neural network prediction model with sparrow search algorithm reduced MAE by 0.28 veh/(3 min), MAPE by 1%, MSE by 2.72 veh/(3 min), and RMSE by 0.04 compared with the BP neural network prediction model; the optimized BP neural network prediction model with improved sparrow search algorithm reduced MAE by 1.31 veh/(3 min), MAPE by 4%, MSE by 9.2 veh/(3 min), RMSE by 0.18, and the goodness-of-fit was closer to 1. The improved SSA-BP prediction model outperforms the SSA-BP neural network prediction model and effectively improves the prediction accuracy of the BP neural network with a goodness-of-fit of 0.98, which is suitable for traffic volume prediction and can provide reliable prediction values for intelligent transportation systems.

Abstract:In order to enhance the control measures of the public transportation priority policy and understand the mode choice process of urban residents for travel, a research was conducted to investigate the evolutionary game model of mode choice for urban residents. The study was based on the principles of behavioral economics theory and prospect theory, and incorporated the concept of mental accounting by constructing profit and loss accounts. Using evolutionary game theory, an evolutionary game model was developed between travelers and government agencies. The dynamic evolution process and stability conditions of both parties′ strategies were analyzed using replicator dynamics equations. The research identified the constraints of the system′s optimal state and system fluctuation state. Moreover, the main reasons for the deviation from the ideal state of the evolutionary trend in reality were explained from the perspectives of government perception and traveler perception. Additionally, the study identified the main problems of the current government control measures. Numerical simulations were conducted using MATLAB, and an optimization model with a dynamic performance payment mode for government subsidies was introduced. The research findings showed that the stable probability of travelers choosing public transportation was 0.33, and the probability of government participation in control was 0.92. Sensitivity analysis of the utility parameters was also conducted. The results of the study indicate that the government should focus on optimizing its public transportation control strategy by reducing the cost of public transportation, appropriately increasing the cost of private car travel, and shortening the travel time of public transportation. This would significantly increase the probability of urban residents choosing public transportation. In summary, the research provides a theoretical basis for urban transportation planning and public transportation priority policy optimization.

Abstract:To investigate feasibility and applicability of high-speed railway simply supported beam with a combined seismic isolation system in nine-degree seismic regions, taking the type high-speed railway 32 m simply supported beam as a prototype, and the shaking table tests of a 1/10 scale 3 span bridge model were conducted. Fifteen typical near-field ground motion records were selected as the input excitations, and the vertical+vertical and horizontal+vertical were combined input. The seismic displacement, acceleration, reinforcement strain and other response data of key components of the bridge were collected during the test, the damage of the bridge after each earthquake input condition were observed, and the experimental phenomena and measured data were analyzed comprehensively. The results show that the pier remains elastic under earthquakes, and the relative displacement of pier and beam becomes smaller, the transverse and vertical acceleration of the main beam is controlled within 0.3g and 0.5g, respectively, which ensures the driving safety after the bridge adopts the hyperboloid bearing + metal damping limit device + steel anti-falling beam combined damping. The combined seismic isolation system has played a good effect of damping and isolation under the designed seismic action, and dissipated earthquake energy. The relative displacement of pier and beam is controlled below 20 mm, the pier is slight damage, and its displacement ductility ratio is less than 1.2. The combined seismic isolation system works stably to ensure that the main beam does not suffer from falling earthquake and girder hopping risk under the rare action of earthquake, and the pier is moderate damage, and its displacement ductility ratio is controlled below 2.2, without collapse risk. The combined seismic isolation system has achieved the seismic performance targets of 32 m span simply supported beam of high-speed railway in nine-degree seismic regions.

Abstract:The mechanical characteristics of warm and ice-rich frozen sand are the key and difficult problems in frozen soil engineering. In order to study the frozen sand with different ice contents, triaxial tests at -1.5 ℃ were carried out on conventional saturated frozen sand and ice-rich frozen sand. Based on the experimental results, the effects of confining pressure and ice content on the mechanical characteristics of frozen sand are discussed. And the differences in deformation mechanisms between conventional saturated frozen sand and ice-rich frozen sand are analyzed. The results show that: the proposed method of "mixing ice particles and sand, compacting in layers, and replenishing water from below" can make ice-rich frozen sand with uniform distribution of soil particles. The strength and volumetric strain of ice-rich frozen sand differ greatly from conventional saturated frozen sand, but the stress-strain relationship and volumetric strain of ice-rich frozen sand with different ice contents are very close. The ice-rich frozen sand with 67% ice content under different confining pressure are strain-softening type; and with the increase of confining pressure, the degree of strain-softening gradually decreases, and the volumetric strain gradually transforms from volumetric dilation to volumetric contraction. The external force on conventional saturated frozen sand is shared by soil particles, ice and unfrozen water, while the external force on the ice-rich frozen sand is mainly borne directly by ice, in which the entrained soil particles indirectly affect the mechanical characteristics of ice.

Abstract:To reveal the effect on the bearing characteristics of piles from thermal and rheological properties of frozen soil, experimental analysis on thermal and rheological responses was conducted. Using a self-designed large-scale test apparatus, several laboratory model tests on the bearing characteristics of piles in the frozen ground were performed under different temperatures and loading processes. The thermal and rheological responses of axial force and shaft resistance were analyzed. Results show that, firstly, the ground temperature has a significant effect on the foundation stiffness. With a higher ground temperature (about -3 ℃), the pile stiffness reduces to only 1/10 of that when the temperature is lower (about -6 ℃). Secondly, with the lower ground temperature, the axial force decreases rapidly along the depth, and shaft resistance is large on the top and small on the bottom, that is, the upper part of the pile ( about upper 1/3) bears the major load. On the contrary, with the higher ground temperature, the axial force distribution becomes relatively gentle along the whole pile length, and the shaft resistance on the deeper pile obtains an increasing exertion correspondingly. Thirdly, the rheological effect has a significant influence on the development and variation of shaft resistance. Due to the rheological effect, shaft resistance has a significant decrease of more than 200 kPa in the load-holding stage. Furthermore, the rheological effect is also affected by ground temperature and load level. When the ground temperature increases, the relaxation of shaft resistance resulting from the rheological effect is nearly 50% of the initial value. When the load level increases, the rheological effect presents a developing trend that increases first and then decreases. The bearing characteristics of piles in frozen soil have significant thermal and rheological responses, which must be considered in practical engineering design, operation, and maintenance. The results of this study can provide theoretical support for engineering practice.

Abstract:In order to solve the problem of electromagnetic vibration caused by radial electromagnetic force of interior permanent magnet synchronous motor, a motor topology structure with Halbach magnetizing mode for piecework permanent magnet and auxiliary slots for rotor was proposed. Firstly, the principle of air gap magnetic density, radial electromagnetic force and electromagnetic vibration of the motor is deduced and analyzed, and the finite element model is established. Secondly, an electromagnetic vibration analysis scheme based on the coupling of electromagnetic field and mechanical field is proposed, and the time and space order Fourier decomposition of the radial electromagnetic force of the motor is carried out. In the mechanical field, the amplitude of the vibration acceleration of the motor stator at different frequencies is analyzed, and the modes of the stator are calculated. On this basis, the hierarchical optimization scheme of motor parameter sensitivity was constructed based on response surface method and multi-objective genetic algorithm, and the Pareto frontier of sample points was obtained to determine the optimal parameters of the motor. Comparing the optimized motor with the ordinary V-type interior motor. Finally, the equivalent stress and total deformation of the rotor were simulated in the mechanical field, and the proposed motor structure was verified to meet the mechanical design requirements. The analysis results show that the radial electromagnetic force amplitude of the proposed structure motor is greatly reduced on the basis of no loss of electromagnetic torque, which restrains the groove torque, improves the air gap magnetic density and the sinusoidal degree of back potential, improves the electromagnetic performance of the motor and restrains the electromagnetic vibration.

Abstract:In order to further analyze the different factors affecting ship electric field and improve the accuracy of electric dipole modeling method in ship underwater electrostatic field simulation analysis. The corrosion electrochemical principle and characteristics of underwater corrosion electrostatic field are studied. The expression of galvanic corrosion current of ship-propeller is derived from the angle of corrosion current density. The analytical expressions of horizontal and vertical electric dipole electric field are solved by mirror image method under air-seawater two-layer model. The analytical model of the electric field based on the corrosion current dipole of the ship is established. On this basis, the electric field on the underwater 50 m line of a medium-sized ship is analyzed by numerical simulation. The results show that within the set range of variation, the influence degree of the corrosion potential of the hull and propeller, the immersion area of the hull and propeller, the seawater temperature and the seawater conductivity on the underwater corrosion electrostatic field of the ship are about 29%, 23%, 53%, 82%, 30% and 67%, respectively. The simulation results and the analytical model of the electric field can provide strong theoretical support for the further study of the electrostatic field characteristics and protection methods of underwater corrosion of ships.

Abstract:To improve the basic performance of the magnetic levitation car, based on the current research situation of permanent magnet electrodynamic suspension (PMEDS),this paper propose a better annular structure of permanent magnet electrodynamic wheel(PMEDW). In term of theoretical analysis, this paper analyzes the theoretical rationality of Halbach array magnetization varying by different magnetization angle, the number of permanent magnets in the monopole pair can be increased to increase the peripheral magnetic field intensity by optimizing the magnetization angle, a more concise analytical formula is derived by using the equivalent surface current method, and the structural relationship, magnetic field characteristics and eddy current distribution characteristics between the PMEDW and the conductor plate are obtained through analysis. In terms of 3D simulation optimization, different types of PMEDW were established in ANSYS Maxwell. The magnetic field, levitation force, propulsion force, levitation to weight ratio and levitation to propulsion ratio were compared respectively in simulation analysis and analytical calculation results to verify whether the new type of PMEDW is able to improve the function of levitation-propulsion integration simultaneously, the accuracy and reliability of the 3D electromagnetic simulation are verified from the perspectives of analytical calculation and experimental testing. The optimization scheme of Halbach array permanent magnet electric wheel will contribute to improve the basic performance of the magnetic levitation concept car, and provide a feasible technical choice for the formation of new green and environmentally friendly vehicles under the background of "emission peak and carbon neutrality".