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1、 Chen Rongshen（陈荣生） 1. College of Transportation, Southeast University, Nanjing 210b9b, China 2. College of Civil Engineering, Nanjing University of Technology, Nanjing 210009, China In developing countries，rural road construction is mostly cumbered by shortage of funds. Engineers concerns most in r

2、ural areas is how to build roads which not only cost less but also meet the traffic demands. Especially in vast rural areas of China, there are a great variety of transportation patterns, and the traffic composition is very complex. Compared with other countries，the traffic composition in China rura

3、l areas have its own features. Therefore，there is no experience about the rural roads construction for reference. In recent years，the central government of China has increased the strength for rural road construction. At the same time，a lot of researches about rural road construction have been done

4、by researchers in China, and some conclusions about china rural roads have been made. In the authors opinion，the selection of the pavement structure material is the key measure to reduce the construction cost of rural roads after the route has been determined. Compared with concrete pavement，asphalt

5、 pavement relatively costs less and is the first choice for rural roads in China. And then，according to the research achievements about rural roads construction，the authors have done some preliminary researches on the structure design for low-cost asphalt pavements for rural roads. 1 Traffic Composi

6、tion of Rural Road Rural roads include county roads，town roads and village roads. The traffic on rural roads is usually mixed. On a county road, traffic volume is between 300 to 1500 veh/d in average，and in a county with a developed economy，it reaches 1000 to 2 000 veh/d. The traffic volume between

7、county and town is 100 to 300 veh/d，and the traffic volume between towns is usually less than 100 to 300 veh/d. In a mixed traffic flow，trucks 1 account for 40% to 70% of the traffic volume, which are mainly light trucks carrying less than 2. 5 tons（including agricultural vehicles such as electro-tr

8、icycles，walking tractors etc.）and medium-size trucks of 2. 5 to 5 tons. Most of these light or medium trucks are overloaded. The proportion of heavy truck is less than 9%.On some roads to counties，the proportion of overloaded trucks is 5% to 32 %，while on some county roads connecting to national or

9、provincial trunk highways，the proportion of overloaded vehicles usually amounts to 20% to 32% . The traffic volume on rural roads is not heavy. However，considering the practical situation in China, as well as the exitence of overloaded vehicles，100kN，or BZZ-100 was adopted as standard axle load in t

10、he research. The pavement deflection or the flexural-tensile stress at the bottom of asphalt surface is taken as the design parameter. The axle load was calculated in accordance with the following formula: N4.35s ,CC（P/P）is12Ni和-the axle weight of an i-level axle in kN and the action frequency;-the

11、axle weight of standard axle in 100 kN and the action frequency; If the distance between axles is less than 3 m， axle loads are calculated as a double-axle or multi-axle loads，and If the flexural-tensile stress at the bottom of semi-rigid base is taken as the design parameter, the axle load is calcu

12、lated in accordance with the following formula:If the distance between axles is less than 3m， 2 Traffic Volume on Rural Roads Minibuses are adopted as the standard vehicle for the design of rural roads. 2 Table 1 shows its external dimensions. Table 1 External dimensions of the passenger car m Lengt

13、h Width Height Front overhang Distance between axles Rear overhang 6.0 1.8 2.0 0.8 3.8 1.4 The typical vehicle types on rural roads are listed in Table 2. And others such as non-power-driven vehicles，animal-drawn vehicles，and bicycles can be taken into account in the calculation of traffic volume on

14、 rural roads，in view of their roadside interference. In accordance with the traffic composition and volumes，rural roads are divided into five grades. The traffic volume of each grade is shown in Table 3. Traffic volume specified in Table 3 was obtained by taking the minibus as the standard vehicle t

15、ype,and converting different types vehicles according to the vehicle conversion coefficients given in Table 2.In Table 3， t,，365N1，,1s,N,e ,Ne refers to the cumulative equivalent axle load action frequency;Ns refers to the equivalent axle load action frequency in the designed traffic lane in the beginning operation period of rural roads;y refers to the average annual growth rate of traffic volume; refers to lane coefficient, and 1.0 for a single lane and 0. 6一0. 7 for a dual lane. 3 Strength of Ro