Study On Typical Asphalt Pavement In Seasonally Frozen Area Based On Life-cycle Benefit

Transportation is the lifeline of the national economy to promote development. Amongthe five modern transportation ways, highway is favored because of its advantages. Althoughhighway development is keeping healthy in recent years, the problems to improve highwaylevel should not be overlooked.High temperature and cold climate are the two most important factors that influence theperformance of subgrade and pavement of Chang Chun seasonally frozen region. Highway inthis area has its own unique problems. But the current “Specifications for the Design ofHighway Subgrades"(JTG D30-2004) and “Specifications for the Design of AsphaltPavement"(JTG D50-2006) are suitable for any region in our country, but no special termsfor seasonally frozen region.In this paper, a comprehensive survey of the diseases of the highway subgrade andpavement was untaken, and a corresponding relationship between the diseases and themechanics index of subgrade and pavement structure was set up based on the seasonallyfrozen region of typical pavement structure design. In the design of pavement structure, theindex system that can reflect the actual operation state of pavement structure was established.And two kinds of typical pavement structure for seasonally frozen region were recommended.The main content is as follows:1. To make a comprehensive investigation on the main diseases of asphalt pavementstructure in seasonally frozen area, and set up the corresponding relationship between diseaseand design index according to the factors of climate, traffic and load.2. To recommend two kinds of typical asphalt pavement structures suitable for the climate features according to the main diseases and the previous experience.3. To calculate the mechanical responses of the typical pavement structure under the loadof130KN using BISAR.4. To analyze and appraise the sensitivity of all calculated load responses to the highwayperformance with the grey theory to obtain the preferential sequence of them. At the sametime, to obtain the preferential sequence of all these typical pavement structure under anyindex system using the theory of grey target to simplify the design procedure of highwaypavement.5. To make economic evaluation of the recommended typical structures based on thelife-cycle benefit theory to get the preferential economic sequence of these structures.The main conclusions are as follows:1. The diseases of subgrade in seasonally frozen region are produced due to thecomplicated factors of temperature (positive and negative), nature of soil and humidity. Heave,frost boiling, uneven settlement and longitudinal cracking are the main diseases of subgrade.The relative sensitive indexes to the design of subgrade performance are the compressivestress and compressive strain on the top surface. According to the cause of disease, diseases ofasphalt pavement can be divided into five types as type of loading, type of high temperature,type of low temperature, type of water damage and type of fatigue. Diseases of asphaltpavement are produced to a large extend by the vehicle load, especially the overloaded or/andthe oversized vehicles.2. The design method of typical pavement structure of Changchun seasonally frozenregion are established in the framework of the existing specifications. The typical pavementstructure of this region should have the following three characteristics:①Adapt to thecharacteristics of the traffic load.②To keep stability under any natural conditions.③Tosatisfy the characteristics of between the layers. All of the two kinds of typical pavementstructure recommended in this paper have been calculated with the design method proposedby the current specifications and they all satisfy the requirements.3. The vertical displacement at the center of wheel gap, stress at the layer bottom, strainat the layer bottom, the compressive stress and strain subgrade top surface is calculated withBISAR. Considering of the present situation of China, the wheel axle load here is130KN, abbreviated as CKZ-130. As shown by the results, load responses of the pavement structureunder static load are far less than the values calculated under repeated loads with the fatiguedesign method. And calculated data of the recommended long-life pavement structure can allmeet the requirements of design index system.Extend of the impact of the various parameters on load responses are calculated andcompared by the three-layer system. From the results, conclusion can be achieved that if themain factors among the parameters in the pavement design can be found out, then the designmethod and procedure of typical pavement can be simplified and optimized easily.4. The sequence of the degree of the influence of the load responses on the asphaltpavement performance are determined by the grey theory, as follows:the road vertical displacement at the center of Wheel gap> compressive strain on the topof subgrade> compressive strain at the bottom of the asphalt layer> the tensile strain at thebottom of base layer> the compressive strain on the top of subgrade> the compressive stressat the bottom of asphalt layer> the tensile stress at the bottom of base layer.The grey target sequence is set up on the basis of the standard sequence, which isestablished by1standardized target center in accordance with the minimum polarity principle.Also, degree relative to the center of the target is calculated which can represent how closeany sequence and the standardized one are.5. The concept of Life-cycle benefit is introduced in the economic evaluation of thetypical pavement in seasonal frozen region. And the indexes to evaluate are selected to workout the life-cycle cost of all typical pavement structures. Therefore, the economic sequencesof the typical pavement structures are determined. In the study of life-cycle benefit, the netpresent value is selected as the economic evaluation index. Periods for analysis are differentbetween the two types of typical pavement structures with15years for the “strong foundationand thin face”"type and45years for the long-life one. Life-cycle cost can be divided into5parts: the initial construction cost, cost for minor repairs and routine maintenance, cost forrepair, cost for major repair and cost for users. The sequence of cost is as follows:B-4<B-1<B-2<B-3<A-1<A-2<A-3<A-4.The results show that although the initial construction cost of the long-life asphaltpavement is much higher than that of the traditional pavement structure, the life cycle cost is better than the latter.The application of technique of the hot-mixed plant regeneration in the repair orreconstruction of highway pavement is studied, and the economic benefits are considered andanalyzed to provide an effective approach to save cost in the construction of highway inseasonally frozen region.