Research On Granular Base Design Method And Permanent Deformation Control Model

Restrictions on permanent deformation of asphalt pavement structure with granular base is basic requirement of structure design, the damage model is of such pavement structure design method of common selection. Permanent deformation of granular layer was mainly reseached in the thesis, main purpose was putting forward design index and model for controlling permanent deformation of granular layer. The major work included:Firstly,141 kinds of typical pavement structure of granular layer were selected for stress level analysis, and 43 kinds of combination of semi rigid base granular layer flip chip structure and granular material flexible base of two kinds of typical structure were analysed, and changed each structure layer thickness and modulus of two kinds of typical structure, to analyzing the impact of stress level of granular layer, obtained the influence law of various factors on the granular layer stress state,and putted forward the granular layer thickness range and substratum suitable modulus. Then, determined the typical stress level: σ1=100～250kPa, σ3=0～100kPa, and the main stress ratio σ1/σ3=1.2～7.9, were mainly distributed in 1.4～5.1, thus the loading sequence of dynamic modulus and the permanent deformation test loading conditions were determined.Secondly, dynamic modulus and CBR were selected as performance parameters of granular base material design, researched the impact of different content, different stress state and different degrees of compaction on dynamic modulus, obtained the influence laws of different gradation and different horizons of the granular layer modulus value range. Changed key sieve passing percent of different gradation and analysed the impact of dynamic modulus and CBR of granular base material, with the optimization of gradation, got the key sieve passing percent control.Thirdly, the influence law of principal stress ratio, confining pressure, gradation and water content on permanent deformation characteristics was analysed. Permanent deformation has been basically formed in 1000 loading time, and accumulative deformation changes slowly after 20000 times. The regression analysis of M-E model parameters was made based on the test results. On the other hand, the prediction models based on the permanent strain stress state was rebuilt, and the adjustment coefficient of moisture content and the gradation change was put forward.Fourth, test schemes for research on permanent deformation of granular layer were demonstrated. For the purpose of research on permanent deformation of two types of granular base, the principal stress was separately 30kPa、50kPa and 70kPa, and different deviator stresses were used as loading path. Permanent deformation properties of two types of gradation were analysed. Because of the limit of test loading times, test curves were extended by way of mathematics model created by Perez, I. between permanent strain and numbers of standard axle load and methods of nonlinear statistical regression. Finally, when permanent strain rate with stress loading path attained 1×10-5/10-3 (per loading period), it was thought that permanent deformation of granular layer reached zone boundary of A-B(shakedown limit).Last, permanent deformation of 162 kinds of typical pavement structure of granular layer were calculated, and analysed the permanent deformation ratio of each layer in the total of whole pavement structure, draw up 6mm as a critical amount of permanent deformation standard, determined the corresponding laboratory tests critical permanent strain 0.03, and adjusted the granular layer of permanent deformation to total deformation ratio. In use of epitaxial permanent deformation test curve, got the number of standard load corresponding to the critical plastic strain criteria.stress ratio (deviator stress/confining pressure) as design index was put forward to control permanent deformation of granular base, established the control model of permanent deformation based on key sieve of 4.75mm.In this paper, based on shakedown theory, found the plastic stability and plasticity of creep critical stress ratio of permanent deformation in granular base, established the control model of granular base permanent deformation in plastic state. Under the model, pavement structure design is in plastic stable state, and does not produce big permanent deformation, has vital significance to the design and application of granular base flexible pavement structure.