1、1 外文文献 structural Design of Asphalt Pavement for Low Cost Rural Roads Yuan Goulin(袁国林 )12 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， ru
2、ral road construction is mostly cumbered by shortage of funds. Engineers concerns most in rural 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 compo
3、sition is very complex. Compared with other countries， the traffic composition in China rural 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 co
4、nstruction. At the same time， a lot of researches about rural road construction have been done 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
5、cost of rural roads after the route has been determined. Compared with concrete pavement， asphalt 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 r
6、esearches on the structure design for low-cost asphalt pavements for rural roads. 1 Traffic Composition 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，
7、 and in a county with a developed economy， it reaches 1000 to 2 000 veh/d. The traffic volume between 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 account for 40% to 70% of the traffic volume, which a
8、re mainly light trucks carrying less than 2. 5 tons(including agricultural vehicles such as electro-tricycles， 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，
9、 the proportion of 2 overloaded trucks is 5% to 32 %， while on some county roads connecting to national or 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
10、China, as well as the exitence of overloaded vehicles， 100kN， or BZZ-100 was adopted as standard axle load in the 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 fo
11、llowing formula: isNN 35.421 )/( si PPCC 和 -the axle weight of an i-level axle in kN and the action frequency； -the 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
12、the flexural-tensile stress at the bottom of semi-rigid base is taken as the design parameter, the axle load is calculated 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 de
13、sign of rural roads. Table 1 shows its external dimensions. Table 1 External dimensions of the passenger car m Length 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-
14、driven vehicles， animal-drawn vehicles， and bicycles can be taken into account in the calculation of traffic volume on rural roads， in view of their roadside interference. 3 In accordance with the traffic composition and volumes， rural roads are divided into five grades. The traffic volume of each g
15、rade is shown in Table 3. Traffic volume specified in Table 3 was obtained by taking the minibus as the standard vehicle type,and converting different types vehicles according to the vehicle conversion coefficients given in Table 2.In Table 3， 1136 5 tseNN Ne refers to the cumulative equivalent axle
16、 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
17、 lane. 3 Strength of Roadbed The modulus of resilience of roadbed varies greatly. For convenience， the strength of roadbed can be divided into four classes according to its moisture content and modulus of resilience， as shown in Table 4. The parameters in Table 5 are determined by combining design p
18、rinciples with practical experience. By applying elastic multilayer theory to the pavement structure specified in Table 5， the influence of Ne on the pavement thickness of rural roads was analyzed， and the result show that for given h， h2， E0， the roadbase thickness for neighboring traffic classes c
19、hanges in a range of 4-5 cm. This result indicates that the classification of traffic volume on rural roads shown in Table 3 is reasonable and feasible in terms of the design and construction of asphalt pavement structures. By using the elastic multilayer theory， the asphalt pavement structure of or
20、dinary rural road in Table 5 is analyzed. When Ne， the cumulative equivalent axle load action frequency， the thickness of road surface(h =3 cm)， and the thickness of subbase(h2 = 20 cm ) remain the same , the influence of neighboring roadbed strength classifications on the thickness of roadbase is 3
21、 cm 一 5 cm. This conclusion indicates that the strength classification of roadbed is reasonable and applicable to the design and construction of asphalt pavement structure. 4 Determination of Thicknesses of Asphalt Pavement Structure Sensitivity analysis of the design parameters of roadbed and pavement structures is
