【正文】 uction of asphalt pavement structures. 4 By using the elastic multilayer theory ， the asphalt pavement structure of ordinary 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 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 to find out the relationship between structural strength of asphalt pavement structure and the design parameters of each layer, and determine the most sensitive layer in the pavement structure. The asphalt pavement structure of rural roads is generally posed of a road surface, a roadbase，and a subbase， as shown in Table 6. The pavement structure was analyzed according to elastic multiplayer theory under the double circular uniform load， with an assumption that there is continuous contact between the adjacent layers of the asphalt pavement structure. The basic parameters used in the calculation and analysis of asphalt pavement structure are listed in Table 7. By analyzing the effects of the change of all the parameters of pavement structure on the distortion of the road surface， roadbase， and roadbed , the following conclusions have been drawn. (1)Increasing the thickness of the road surface effectively decreases the road surface deflection， but raises the cost. The paratively economical and effective method is to increase the thickness of the subbase, which is superior to increasing the thickness of roadbase， while increasing the thickness of the road surface is the last choice. (2)As the thickness of pavement structure increases， the change of road surface deflection will trend to be gentle. When the thickness of road surface reaches a certain value， the variance in the road surface deflection will not be obvious， and then it is ineffective to enhance the bearing capacity of asphalt pavement structure by increasing the thickness of road surface. It is remended that the thicknesses of the roadbase and the subbase should be equal to or larger 5 than 18 and 20 cm, respectively， in design of asphalt pavement structures of rural roads. Fig. 1 shows the effects of the changes in the thickness of each layer on road surface deflection. (3)Road surface deflection is very sensitive to the change of modulus of the roadbed. The increase in the modulus of roadbase or subbase is also effective to decrease the deflection of the road surface. On the other hand， the deflection of the road surface decreases gradually when the modulus of the surface increases， being the least effective factor. When the modulus of the road surface increases to a certain value， decrease in road surface deflection is not apparent. Fig. 2 shows the effect of the modulus of each layer on road surface deflection. From the above discussion， we conclude that the most sensitive layer for road surface deflection is subbase， and the next is roadbase. To decrease the road surface deflection of lowcost rural roads， the strength and stability of the roadbed should be enhanced, and the materials with a certain thickness and relatively high density should be used to pave the subbase. The traffic volume or the accumulative equivalent axle load action times(frequency)within the designed life of road is used to determine the type and thickness of the asphalt pavement road surface, and the results are listed in Table 8， where veh/d means the number of the equivalent the passenger cars per day. For a low traffic volume rural road with Ne 500 000， graded broken stones(or gravel)can be used as a flexible base. The flexible base has good strength and effectively prevents reflection cracks of the asphalt pavement road surface, provided the graded broken stones(or gravel ) meets the requirements for high density(degree of pac