【正文】 and the subbase should be equal to or larger 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 5 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 paction ,100%. To ensure the sufficient strength and stability of the flexible base， its thickness is not less than 15 cm， the thickness of the aggregate subbase is not less than 20 cm， A semirigid base usually has a good bearing capacity For the rural roads with Ne)500 000， or those with low traffic volumes but relatively,the minimum thickness of semirigid base or subbase is 1618 cm 5 Calculation of the Thickness of Road Surface Deflection (1)Road surface deflection Road surface deflection is a vertical distortion caused by vertical load on the road surface. It not only reflects the whole strength and stiffness of asphalt pavement structure and roadbed， but also has a close internal relation with the service condition of the pavement. (2)Design deflection The design deflection is the index representing the stiffness of the pavement structure. It is also the deflection of the pavement which is established according to the accumulative equivalent axle load estimated to pass over a lane in the expected design life, road types, road classification， and the types of road surface and roadbase. The design deflection is not only the main basis for the design thickness of the pavement structure， but also the necessary index for the examination and acceptance of the project. Through theoretical analysis and experimental study，formulas for the design deflection value which are applicable to the pavement structure design of lowcost rural roads are as follows: semirigid base: 6 flexible base: where A, is the type coefficient of the road surface. The type coefficient of asphalt concrete road surface is 。1 外文文獻 structural Design of Asphalt Pavement for Low Cost Rural Roads Yuan Goulin(袁國林 )139。 y refers to the average annual growth rate of traffic volume。交通運輸學院，東南大學，南京 210b9b，中國 2。相比 ,瀝青混凝土路面相對費用少、是第一個在中國農村道路的選擇。重型卡車的比例小于 9%。如 電動車 ,摩托車 和自行車可以考慮 為邊對農村道路交通量的計算 的 路邊 干 擾。采用多層彈性理論對路面結構表5 中指定的影響 ,在暗夜精靈 ,農村道路鋪裝厚度進行了分析 ,結果表明 ,在給定的 h,h2,E0、路面基層厚度變化為周邊交通類一個范圍內的 4 5厘米。使用的基本參數(shù)的計算與分析瀝青路面結構都列在表 7. 通過分析影響所有的參數(shù)變化對路面結構的扭曲 ,基層路面和路基 ,下面 ,結果顯示。增加基層模量或基層也是有效降低路面的變形情 況。柔性基礎具有良好的強度和有效防止反射裂縫瀝青路面的路面 ,提供了分級石頭(或礫石 )符合規(guī)定的要求對高密度 (壓實度 (100%)(21。 (3)許用撓度 許用撓度的最大撓度 在最不利 季節(jié)條件下的允許在這條路的使用壽命 。 (3)當累計頻率的等效軸重在 10000002020000 次／ 車道 ,瀝青混凝土路面 5 厘米厚的 cm7 是被推薦的。 [3]劉 :如何降低工程造價的農村公路 [J].中國公路交通的研究與開發(fā) ,2020(2):41 一 44(中