Study On Shakedown Behavior Of Granular Material Used In Pavement And Shakedown Analysis Of Pavement Structures

Nowadays semi-rigid base is the main base used in asphalt pavement in China; theresearch on deformation characteristic of pavement structure is almost focus on the asphaltsurface, but neglecting the research on deformation characteristics of granular base. As theexcellent drainage properties elimination of reflective cracking features and excellenteconomic of granular base material are realized by engineers, pavement with granular basedwould be an important form of pavement structures in China.Shakedown theorem is a basic theory which can analysis the deformation characteristicsof elastic-plastic structures under cyclic loading. Shakedown theory can be used to describeand analyze the deformation behavior of granular base material; shakedown analysis is animportant branch of plasticity mechanics which often used to research the plastic behavior ofthe structure under changing load. The shakedown load based on the shakedown analysiscould reflect the actual carrying capacity of pavement structures.Based on the background introduced above, this paper study the shakedown behavior ofthe granular base material by experiments and theoretical analyses, and apply the shakedowntheorem to analyze the shakedown behaviour of pavement structure. This paper analyze theshakedown behavior of pavement structures based on Melan static stability theory, and try totake Range A shakedown (plastical shakedown)strain of granular material as a controlparameter of deformation of flexible aggregate base which can apply in designing of flexiblegranular base asphalt pavement. The major research work and innovative results are asfollows:1The granular aggregate is selected as the funuction of traditional flexible pavementbase a stress absorbing layer of inverted pavement structure and as a subbase of a semi-rigidbase which are three typical structures of asphalt pavement structures in China. Based on thetheory of elastic layered, using BISAR pavement calculation procedure, this paper analyzingthe stress distribution of granular base in the above pavement structures. Meanwhile thispaper analyzing the impact of surface layer thickness and modulus granular base thicknessand modulus subgrade strength and the factor of overload on the vertical stress distributionwhen flexible granular base material is taken as the base of asphalt pavement structure. At lastthis paper analyze and summarize the range of vertical stresses of granular base, thoseresearches can provide a basis reference of ratchet shakedown behaviour load experiment ofgranular materials. 2Based on classical CBR test method and MTS multi-functional materials testingsystem, then improving the loading device, the shakedown behavior test of granular basematerials used in pavement is conducted considering the external loading conditions (loadwave forms loading rates stress ratio mean stress stress amplitude and their histories onstrain cyclic characteristics) and internal material factor (three different grading). The testresults reveal the characteristics of ratchet shakedown behavior of granular materials undercyclic stress, those researches can provide a reliable experimental evidence of the shakedownnumerical calculation method in this paper.3Research on deformation behavior of granular materials used in pavement has doneunder15different stress levels. Three types of shakedown behaviours that are Range A(plastic stability) Range B (plastic creep or alternating plastic failure) and Range C(incremental plastic collapse) can correspond to describe the deformation behavior of granularmaterials under different stress levels; the paper also analyzes two critical loading stress of thethree types of plastic deformation-plastic shakedown critical stress and plastic creep criticalstress; then the three types of shakedown behavior deformation model equations is alsogiven.4The article briefly describes the basic concepts of shakedown theorem, after thatshakedown analysis of pavement structures is conducted based on Melan static shakedowntheorem. The impact of two types of load distribution patterns (the Hertz contact distribution,trapezoidal equivalent distribution) and structural layer material parameters (angle of internalfriction, cohesion and structural thickness) on shakedown load is discussed. Then compare thetwo types of stability upper bound solution wtih the elastic limit, aslo the static shakedownanalytical load is solved under different constraints5Based on melan static shakedown theory, taking ANSYS finite element tools andMatlab as analyzing platform this paper develop a simple numerical calculation method ofshakedown load of pavement structure that is elastic-plastic finite element method.Afterwards under Drucker-Prager yield criterion this chapter anlysis and solve theshakedown load of the single-layer granular of the pavement structure and the double-layerflexible asphalt pavement.6On the basis of comments on the plastic shakedown(RangeA) strain, then analysis thepossibility of taking it as a design parameter of pavement structures. The shakedownparameter can use to constraint the deformation of flexible granule-base. This paper try to apply the shakedown parameters of aggregates base in designing of flexible asphalt pavement,then gives the design flow chart and the design calculation example.