Study On The Shear Strength Design Standard Of Granular Base

Owing to the disadvantages of Semi-rigid Base Asphalt Pavement during usage such as bad drainage and cracking easily, asphalt pavement with flexible base is now restarted to develop in China. Granular base has its property of good drainage, dissipating stress, and preventing reflect crack. With the development of construction technology and level such as actualization of plant-mix and mechanization of paving, and using of large tonnage compaction machine, current graded granular base is different from the traditional one, and has already been paved as test-road on several freeways in China.As a flexible pavement structure, granular base has a mainly defect of being easy to generate biggish plastic deformation. The essence of plastic deformation is shear deformation between granular materials, so it is important to control shear strength of granular base. Furthermore, vibrating compaction is widely used in road construction, but the standard of heavy compaction test sample is also used in asphalt pavement design specification in China, which is obviously not conformed with using requirement. This paper studies granular base which uses different compacting methods such as VCT sample and MPCT sample, comparing from the aspects of physics and mechanics properties, and shear strength evaluation method and provides technique for extension of granular base(transition layer) asphalt pavement.Through choosing granular base as three type pavement structure( transition layer, base layer and sub-base layer) and analysis the influence of many factors on stress, the paper suggests a method to enhance using property of granular base and calculates maximum shear stress of granular layer, in order to minimum thickness of asphalt pavement.Vibrating compaction method and heavy compaction method and three types of grade are adopted in physics and mechanics test. Comparing dry density, CBR, modulus of different sample method, and establishing relationship of these parameters.Based on the research for the structure property of granular base, structural stabilization shows the influence of water to modulus, and structural changeability shows the influence of water to plastic deformation, and total structure property of granular base structure is the combination of the two. The result indicates that granular base has positive structure property.Establishing the relationship of CBR and shear strength, and proposing asphalt pavement minimum thickness design method which conformed with shear-bearing requirements of granular base.