Applied Mechanics and Materials Vols. 204-208

Abstract: Foam lightweight soil is a new type of material appearing in recent years, whose advantages are paid more and more attention to by engineers and it will have broad application prospect in the engineering. An in-depth study application of foam lightweight soil in the complex of railway soft soil foundation treatment what based on a railway foundation project in Tianjin, this paper discusses the actual application state of foam lightweight soil in handling of special railway soft soil foundation. Through in-depth analysis of the advantages of a foam lightweight soil, optimization of construction replacement thickness and moisture density, discussion on construction of it, we can find large advantages of foam lightweight soil as replacement material in the complex railway soft soil foundation treatment, and provide new ideas about processing complex soft foundation.

Abstract: Based on asphalt pavement design theory and criterions in China, five asphalt structures are put out, including three mix base pavement structures, one typical semi-rigid base pavement structure and one typical flexible base pavement structure. For contract study, different pavement structures were selected with various combinations of modulus and Poisson ratio, but the total thickness is same for comparative analysis. The stress-strain at different depth in asphalt layer is calculated by using BISAR program. The data analysis is carried out for the maximum tensile stress, and the maximum strain of asphalt layer, and the maximum compressive strain on top of sub grade, deflection on asphalt surface. And budget basis price for base is contrasted too. The data analysis results show that the mix base asphalt pavement structures can be designed to get better pavement mechanical performance than typical semi-rigid base and typical flexible base asphalt pavement structures, while the price is higher than that of semi-rigid base. If we consider fatigue life, the cost performance for mix base of upper base with asphalt stabilized macadam is the best. This gives out the important reference for widespread the mix base in future.

Abstract: In order to study the factors which influence the inorganic binder stabilized material’s compaction test results, different recycled material content therefore different reclaimed gradation mixtures are tested while varying the amount of cement. The experiment results show that contents of the recycled base material and the recycled surface material on the compaction test results are determined by the change of their density and water absorption ratio. Dry density of the recycled mixture increases with the increase of the reclaimed base material density. Low water absorption ratio of the recycled material reduces the reclaimed mixture’s optimum moisture content. Density of the reclaimed wearing surface material reduces the maximum dry density of the reclaimed mixture because the old wearing surface material has lower density. Its low water absorption reduces the optimum moisture content of the recycled mixture. Influence of cement content on compaction test results is the increase of the cement content can enhance the maximum dry density and optimum moisture content of the recycled material. Through the analysis of the results of the compaction test, the key factors in the recycled material compaction test are unveiled.

Abstract: For the construction of the proposed Qinghai-Tibet Express Highway in permafrost regions, it will be necessary to use the new technique of cooling the ground temperature by the coarsely crushed rock layer with a low fines content. The heat convection governing equations based on airflow function in variable permeability porous crushed rock layer are derived. Comparison of the cooling capability of winter-time natural convection in the crushed rock highway embankments with various widths of crushed rock layer and an air-permeable side slope surface were studied using a finite element method. The result indicates that the cooling capability of natural convection within the crushed rock highway embankment with a crushed rock layer width of 12 m is stronger than that with a crushed rock layer width of 10 m. Under the same temperature and pressure boundaries, the storage of cold energy in the foundation soils below the wider crushed rock highway embankment due to natural convective heat transfer is larger than that below the narrower one.

Abstract: The purpose of this study was to evaluate flow characteristics on two-lane rural highways and to develop criteria for highway widening The study is conducted on two tracks: theoretical development of delay models and use of a simulation model to estimate the effect of certain parameters on delay and percent-time-spent-following. Models of delay are presented, as are the regions in which the traffic is stable or unstable. It was also possible from the simulation to obtain the percent-time-spent-following, which is a key parameter in determining level-of-service on two-lane highways.The accrued delay over the usable life of a two-lane highway pavement, assumed to be 20 years, was discounted to present monetary value This was then compared to four typical construction costs for different terrain types. The threshold average daily traffic volumes were determined at the points where the present value of the accumulated delay was equal to the cost of constructing two more lanes. These threshold values can be used as criteria for widening a two-lane highway and converting it into a four-lane facility. Additional criteria, based on percent-time-spent-following, are also presented.

Abstract: In this paper we propose a stepwise genetic algorithms approach for optimizing highway alignments for improving computational efficiency and quality of solutions. Our previous work in highway alignment optimization has demonstrated that computational burden is a significant issue when working with a geographic information system (GIS) database requiring numerous spatial analyses. For solving real-world problems working directly with real maps through a GIS is highly desirable. Furthermore, saving computation time can enhance adoptability of a model especially when a study area is relatively large, or involves many sensitive properties, or if locating complex structures such as intersections, bridges and tunnels is necessary. It is well acknowledged that in many optimization processes subdividing large problems into smaller pieces can decrease the computation time and produce a better solution. In this research two different population sizes are used to develop a stepwise alignment optimization when employing genetic algorithms in suitably subdivided study areas. An example study shows that the proposed stepwise optimization gives more efficient results than the existing methods and also improves quality of solutions.

Abstract: This paper discusses the ageing features of SBS modified asphalt and its assessment index. The performances for both host asphalt and modified asphalt after different RTFOT ageing times was tested and micro analysis was conducted with infrared spectrum. The quantitative analysis for the micro-changes of ageing process was carried out according to Lambert Beer law. The research results show that the longer the ageing time, the smaller the penetration and ductility of asphalt are, and the greater the softening point and viscosity. In comparison with the host asphalt, the absorption peak of SBS modified asphalt in stretching vibration (C=C) at 1600cm^-1, the absorption peaks of polybutadiene in bending vibration at 966cm^-1 and 911cm^-1 , and the absorption peak of styrene in bending vibration at 697cm^-1 are from SBS modifier. The oxygen reaction happens in ageing process of asphalt, producing carboxyl and subsulfoxide. Affected by the higher activity of SBS modifier, SBS modified asphalt can be easily oxidized.There is good correlation between its penetration, softening point, ductility with carboxyl and subsulfoxide , so the above three indexes can be adopted to assess the ageing of SBS modified asphalt.

Abstract: Asphalt aging mechanism and recycling mechanism are studied in the paper, based on four components tests for aging asphalt and recycling asphalt, by comparing and analyzing the D-value between testing data and theory calculated data. Results show that asphalt four components changes regularly for aging asphalt, which some saturates and aromatics are changed into some asphaltenes and colloid. And the recycling mechanism is not regular for the same asphalt, which the mix result of asphalt four components depends on many factors, such as degree of aging, quantity of old asphalt, components and quantity of recycling agent. The study results can provide important theoretical basis for sustainable use and development of regeneration asphalt.

Abstract: In the paper, Combination curved with slope road segment on the driving experiment , The paper is analyzed the curve and slope road segment on Gradient, Horizontal Curve Radius, Speed and heart rate these variables of the inherent relation and law. The model of the relationship of the longitudinal slope and horizontal curve radius and heart rate is set up. By employing regression analysis, Conduct quantitative analysis, calculation and can be determined by the minimum horizontal curve radius value of vertical slope corresponding to at different vehicle-speeds on curved with longitudinal slope,Theoretical reference is provided for designers in the design technology research.

Abstract: This paper studied on the different chosen-unit-weight shear resistant property on different temperature with direct shear test. The results show that the shear strength on 60°C and the dyna mic stability in rutting test on 60°C have familiar trend, the shear strength and the dynamic stability in rutting test have a good relationship on evaluating the high temperature stability of the asphalt mixture. Based on the performance demand ,this paper gives reasonable Bailey parameters Chosen-unit-weight range.