Search

A three dimensional discrete-element (DE) method was developed to simulate the four-point bending fatigue test of asphalt mixture. Firstly, after generating the irregular polyhedron aggregates, a three-dimensional (3D) DE model was constructed based on the typical gradation of AC-16 mixture. Then the contact parameters were chosen from the microscopic model in PFC3D and macroscopic mechanical parameters were obtained from uniaxial compression test. Therefore the conversion relationship between microscopic and macroscopic parameters could be determined. A virtual fatigue test was performed using an optimal algorithm based on basic DEM theory and time-temperature superposition (TTS) principle. To calculate the fatigue life, the authors considered the emergence of cracks inside small beams as fatigue failure criterion. Test results obtained from 3D virtual fatigue test showed agreement with laboratory four-point bending beam fatigue test, showing that this approach could serve as an alternative method to investigate the fatigue behavior of asphalt mixture and also laid good foundation for further studies about the effects of microscopic structures on the fatigue behavior of asphalt mixtures.

Sharp lighting transitions in tunnel entrance zones cause difficulties for drivers in observing the conditions at entrances of tunnels. This phenomenon is called “black hole effect”. It is crucial to develop a proper method to evaluate “black hole effect” in tunnel entrance zones. Firstly, Jiqingmen Tunnel, Weigang Tunnel and Maoshan Tunnel in Nanjing, China were investigated to collect velocity and luminance data within tunnel entrance zones. Then, using collected operating speeds and luminance data, the correlation between the luminance and time is identified and a luminance-time curve is developed and compared with visualization adapting curve. At last, the differences between two curves are compared with the field investigations of three tunnels to evaluate “black hole effect”. Results show that the method of evaluating “black hole effect” has good correlations with results of field tests of three tunnels.

Rutting is a typical distress of rubber asphalt pavement under heavy loads. It is necessary to present a proper method to evaluate the high-temperature performance of rubber asphalt mixture. A newly developed repeated local-load permanent deformation test (RLLPDT) was conducted to evaluate the high-temperature performance of rubber asphalt mixtures. The Origin software is utilized to fit the test curve with creep models. Then the creep model and high temperature evaluation index (D1, Fn) were chosen according to their correlations along with the rutting test results and dynamic stability. The effectiveness and variability of D1 and Fn were verified. At last, the high temperature evaluation standard of crumb rubber asphalt (AR-VS13) and stabilized rubber asphalt (SUP-13 and SMA-13) mixture based on D1 and Fn was given according to the result of dynamic stability.

The study of SMA mixture constuction temperature is very important, for the required construction temperature of SMA mixtures is higher than that of the average ones, which is easily conducive to asphalt aging during construction. Asphalt aging is one of the important factors that will have a great impact on SMA low-temperature performance. Curvature strain indicators of asphalt mixture can be got by low-temperature curvature tests and can be used to evaluate asphalt mixture performance. Failure energy resulting in damages is a comprehensive reflection of asphalt mixture strength and strain. Therefore, it is more advisable to evaluate low-temperature SMA anti-crack performance by referring to its unit failure energy. This paper presents the research on the relationship between different mixing temperatures of asphalt mixtures and their curvature strain indicators as well as the relationship between mixing temperatures and unit failure energy. The research proves that the higher these indicators are the better anti-crack performance asphalt mixtures will have at low temperatures. At last, this paper concludes required construction temperature of SMA 90#.

Longitudinal cracking has been one of the prevalent diseases in the Qinghai-Tibet Highway for decades. It affects the traffic safety and normal operation of the highway. Investigation of damage characteristics and main affecting factors of pavement longitudinal cracking has been done since the opening of the Qinghai-Tibet Highway in the 1950s. Based on the analysis of cross-sectional distribution feature of temperature field, relationship between asymmetric temperature and pavement longitudinal crack was found. Longitudinal cracking of the Qinghai-Tibet Highway especially in sunny—shady slope condition is mainly due to permafrost temperature asymmetry which caused asymmetric distribution of permafrost table and uneven embankment thawing settlement. The longitudinal cracks distribute mainly in the middle or deviation to the sunny slope of the pavement. Based on the mechanism analysis of longitudinal cracking, the prevention proposals for longitudinal cracks of the Qinghai—Tibet Highway are recommended from the aspects of radiation, convection and conduction.

In order to reduce the harm caused by traffic noise, porous asphalt pavement was widely used in the world. For single-layer porous asphalt pavement easy blocking, double-layer porous asphalt pavement structure was brought out. With the top-layer having smaller porosity, the bottom-layer porosity slightly greater, this structure has formed an effective dispersed space for noise absorption. The top-layer has a filter effect on large particles. Dust falling into the surface pore was water out due to the bottom-layer porosity was greater. So the double-layer porous asphalt pavement has self-cleaning effect on pore clogging. The numerical simulation for acoustic absorption properties of porous asphalt pavement structure was made with application of finite element method and acoustic-solid coupling model by large-scale commercial software ABAQUS. The noise-reducing feature was analyzed for the double-layer porous asphalt pavement in porosity and thickness combinations and then structural parameters suitable for double-layer porous pavement was proposed. The result indicated that double-layer porous asphalt pavement has better sound absorption for top-layer porosity of 10%, bottom-layer porosity of 25%, top-layer thickness of 2cm and bottom-layer thickness of 4cm.

In this paper, uniaxial repeated load permanent deformation tests of three mixtures were conducted at different temperatures and stress levels to analyze the permanent strain changing regularity. By the test results, the relationships between flow number, temperature, and stress were also investigated. It is indicated that after coring and sawing, the voids of core specimens are less than the original specimen, and the void of an original specimen should be increased to satisfy the target value of void; all the three asphalt mixtures present three-phase behavior, and the permanent strain is greater and the tertiary stage is hastened at higher temperature and stress; skeleton gradation and modified asphalt can improve the resistance to permanent deformation; the flow number (FN) decreases with test temperature and stress, and it can distinguish the difference between the resistances to permanent deformation of asphalt mixtures. However, at very high temperatures and levels of stress, the difference among the three asphalt mixtures is negligible.

The work zone cost analysis method is an important part of Life Cycle Cost Analysis (LCCA) and plays an important role of correct LCCA costs calculation. Considering that little research has been conducted on the expressway work zone costs model in China, this paper carried out a preliminary research in the field. It first analyzed the important role of the work zone costs at the expressway using LCCA method, and then it analyzed the work zone life-cycle (LCC) costs composition. Related calculation models necessary for analysis of work zone users costs, such as fuel consumption model, user delay costs model and crash costs model and so on were also proposed in this paper.

With the rapid development of urban transportation, conflicts between pedestrians and motorized vehicles have become serious more and more. To effectively improve pedestrian safety, in this paper, based on the data collected from seventy-five streets in Nanjing, Hefei and Changshu cities, the authors evaluate pedestrian safety and point out the main existing problems, such as discontinuous pedestrian lanes and insufficiency of the sidewalks. The authors then present measures for solving the related problems. The purpose of the paper is to provide a background of information for guidance in identification and improving pedestrian safety.

Life Cycle Cost Analysis (LCCA) is an effective tool to contrast pavement structures and achieve high cost-effectiveness ratio of the pavement structure scheme. This paper, based on the consideration that there is little research on expressway asphalt pavement structure evaluation method in China, conducts a tentative study in this field. After an introduction to the research background home and abroad and an analysis of the user cost components of LCCA, the expressway work zone user cost analysis method is proposed firstly at home to replace usual user cost as expressway LCCA method, and a general method frame for expressway asphalt pavement structure evaluation based on LCCA is presented in accordance with the reality in China.

Ambiguous functional classification system (FCS) of urban road will result in serious traffic problems. In China, the current FCS experiences some deficiencies including indefinite roads classes, lack of considerations of the surrounding environment and the unreasonable automobile-priority concept, etc. It does not fully accord with the concepts of multi-modal traffic and context-sensitive design/solution (CSD/CSS) that are recommended and used widely. Consequently, based on the researches of functional classification methods used in the USA, Germany and Poland, this paper analyzes the advantages of the above methods and points out the problems in China. Then, a new FCS is proposed and some key criteria of urban road concerning the service objects and priorities, design controls, road network, types of cross section, land use and bus stations are suggested.

Based on the situation of the present heavy debt burden of toll highway in China, the factors of debt risk formation were analyzed and the warning indexes including debt ratio, debt service ratio, debt income ratio, debt repayment ratio, personnel cost ratio and income interests multiple were established in this paper. The weight of each warning index was determined by using four-grade scores method. According to the established indexes and weights, the warning model for debt risk based on efficacy coefficient method was set up and the means of classing the risk grades were studied. Through the warning model, risk grades can be determined by calculating risk exponent, and different countermeasures can be taken according to different risk grades. At last, the accuracy of the model were verified with a case study. Results showed that the model turned out to be reliable. So investment and debt repayment funds can be arranged reasonably on different warning degrees by departments of transportation. Thus, process of policy decision is improved to be more scientific and the debt risk of toll highway is reduced.

To ascertain the cognition pattern of novice driver, indoor tests were designed in this study. Subjects' reaction time during ongoing test was recorded. By using H6 Head Mounted Optics eye tracking system, subjects' eye movement data was recorded; at the same time, subjects' electroencephalogram (EEG) was recorded by BioGraph Infiniti physical feedback system. With the field data, this paper analyzed the correlation between subjects' average reaction time and the strokes of Chinese character (Ns), average reaction time and the total number of information on the sign (Nt) both during placename searching and placenames reading assignments. This paper also analyzed subjects' visual pattern including average fix duration∖average fixation points∖average pupil diameter. And EEG%', an evolved parameter of subjects' EEG was chose to analyze the correlation between EEG and the information quantity of signs. This paper suggests further consideration of novice drivers' cognition pattern with the analysis results especially when making the standard of legibility distance and legibility time of guide sign.

The three-stage creep behavior of asphalt mixture could be considered as the results of a competition between damage and hardening. Therefore, the damage and hardening variables were both introduced into Burgers model for modification. The series-wound dashpot in Burgers model was modified with a hardening variable and the undamaged mechanistic model was derived from rheological. Then, Kachanov’s equation of damage evolution was adopted and a new creep constitutive model coupled with damage was established by Lemaitre’s effective stress principle. Subsequently, static creep tests of two asphalt mixtures were conducted to validate the modified model, and an algorithm was established to determine the model parameters from typical laboratory data. The proposed model and algorithm were demonstrated through laboratory test results, and the analysis results matched the test perfectly. It is indicated that the proposed model can describe the three-stage behavior well.

Permanent deformation (rutting) in the asphalt pavement is one of the main reasons for pavement damage. The focus of this paper is to study the factors affecting the permanent deformation by tri-axial creep test and the permanent deformation predicting of asphalt pavement. Four popular asphalt mixtures, AC13F, AC13C, AC16 and AC20 were chosen to do the repeated load tri-axial creep test under different voids, asphalt contents, different temperature and load levels. Based on the test result, it was concluded the Flow Number (Fn) of repeated load tri-axial creep test can distinguish the rutting resistance ability of different Hot Mixed Asphalt (HMA) mixtures. Temperature and Load levels have great influence on Fn of HMA as they do for asphalt pavement. The formula used for prediction of pavement permanent deformation was gotten based on the curve between the permanent deformation and loading number under different load and temperature levels. The formula was then calibrated by ALF test data.

Now many expressways are confronted with embankment linking and widening, which cause uneven settlement and pavement cracking along the joint between the old and new roads, especially on soft ground. It is important to systematically analyze the performance of different ground and embankment treatment techniques used in road widening. A numerical model based on plane strain finite element method (FEM) is carried out to analyze the behaviors of embankment and foundation at widening. Four ground and embankment treatment techniques, including embankment reinforcement, light weight embankment, cement deep mixing pile and separating wall are compared in their effectiveness through uneven settlement, horizontal displacement, and stress condition. It has been approved that light-weight embankment has the most effectiveness among four treatments.