车载作用下沥青路面路基土的

永久变形研究

Research  on Perm anent Deformation of Subgrade

Soils  in Asphalt Pavement under Axle Loading

研究生：高启聚

指导教师：郭忠印教授

二○○八年二月

摘要

路面结构在车辆荷载反复作用下产生的过量（塑性）变形累积，会使路表面出现影响行车安全和舒适的不平整度（车辙），或者导致面层底面因出现过大的拉应变（或拉应力）而加速疲劳开裂。因而限制路面结构的永久变形量是路面结构设计中通常考虑的一项基本要求，也是各国力学-经验设计法普遍选取的一种损坏模式。 

路基土是一种典型的弹塑性材料。在车辆荷载的作用下，不仅产生可以恢复的弹性变形，同时也伴随着不可恢复的塑性变形产生。路基土的塑性变形也称为永久变形，路基土的永久变形是路面结构总永久变形的组成部分。虽然路基土的永久变形量在粒料柔性基层沥青路面结构中所占比例较小，然而如果土基产生的永久变形超过一定界限，将会加速路面车辙和面层的疲劳开裂；或者土基发生破坏终将导致整个路面结构的破坏。因此路面结构设计中，控制路基土的永久变形是非常必要的。 

通过选取典型的粒料柔性基层沥青路面结构，利用线弹性层状连续体系程序 BASAR3.0 计算了路基土的三向受力状况，为路基土的永久变形试验提供了加载参考依据。 

研究了路基土的永久变形特性。在对路基土永久变形特性室内试验影响因素分析的基础上，有针对性地选择试验参数，并论证了永久变形试验方案。选取粉土、砂土和粘土为研究对象，并利用室内重复荷载三轴试验研究了三种类型路基土在不同含水量、不同压实度和不同偏应力级位等影响因素下的永久变形特性。研究结果表明：含水量、偏应力和压实度都是影响路基土永久变形的重要因素，而且影响效果非常显著。 

在路基土永久变形特性试验研究结果的基础上，建立了路基土永久变形预估模型。利用室内永久变形试验结果和数学统计回归方法，对 Tseng 和 Lytton以及 AASHTO2002 永久变形预估模型形式进行了改进与标定，分别建立了粉土、砂土和粘土的永久变形预估模型。   

研究了路基土永久变形量计算方法。提出了基于力学-经验法的分层应变总

和法，用于计算粒料柔性基层沥青路面路基土的永久变形量，同时提出了采用路基工作区深度计算公式确定路基土永久变形量的计算深度；最后根据分层应变总和法路基土永久变形量计算方法，把三种类型路基土的永久变形预估模型分别与 AASHTO2002 预估模型进行了对比， 

研究了路基土顶面压应变设计指标。首先提出了控制路基土永久变形的路基土顶面压应变设计指标；然后结合我国不同等级公路的实际情况和设计标准轴载作用次数，应用所建立的路基土永久变形预估模型和计算程序 BASAR3.0，计算了不同粒料柔性基层沥青路面路基土的永久变形量；拟定了 1.4mm 的路基土永久变形量容许标准；建立了路基土顶面压应变设计指标值计算公式： ，同时给出了85%和95%两种保证率下的路基土顶面压应变设指标值计算公式： （85%保证率）和 （95%保证率）；并在此基础上研究了控制路基土永久变形量的粒料柔性基层沥青路面结构设计方法，给出了设计步骤与设计流程。

最后，关于进一步工作的方向进行了简要的讨论。

关键词：沥青路面，粒料基层，路基土永久变形，重复荷载三轴试验，路基土永久变形预估模型，分层应变总和法，设计指标，路基土顶面压应变

ABSTRACT

Accumulation of plastic deformation  of pavement structures under reapted loading can lead to rut. It will  influence vehicle driving safety and comfort and result in too large tensile  strain (or tensile stress) on the bottom of surfacing course. All above will  acculate fatigue deterioration of pavement. Therefore, limiting permanent  deformation of pavement structures is considered when pavement structures are  designed. Permanent deformation of pavement structures is also a basic  distress model in mechnical-emprical design method in a lot of country.

Subgrade soils is a typical  elastic-plastic material. Recoverable resilient deformation and  non-recoverable plastic deformation can produce at the same time under axle  loading. Plastic deformation of subgrade soils is also called permanent  deformation, and it is a very important component in total permanent  deformation of pavement structures. Permanent deformation of subgrade soils is  of little proportion in total permanent deformation of asphalt pavement  structures with granular base. However, if subgrade soils produce more deformation,  appearance of rut and fatigue crack of surfacing will accelerate; or if  subgrade deteriorates, asphalt pavement structures will further deteriorate.  Therefore, when asphalt pavements are designed, it is very necessary to limit  permanent deformation of subgrade soils in pavement structures.

Through  selecting   typical asphalt pavement structures with granular base, subgrade soils stress  in different directions is calculated by way of mul-layer elastic system  calculation program BISAR3.0 in order to provide loading reference for  permanent deformation tests of subgrade soils.  

Permanent deformation  characteristics of subgrade soils are researched. Based on analyzing factors  influencing permanent deformation characteristics of subgrade soils in lab,  test parameters are choosed and proved. Silt soils, sand soils and clayed  soils are adopted to use as studying target. Permanent deformation  characteristics of silt soils, sand soils and clayed soils are studied with  different moisture content, different compaction degree and different  deviator stress by way of repeated load triaxial test. The research results  prove that moisture content, compaction degree and deviator stress are all  very important factors influencing permanent deformation of subgrade soils  and bringing about a striking effect.

Evaluation models for permanent  deformation of subgrade soils are created on the basis of test results of  permanent deformation characteristics. Firstly, According to the test results  of permanent deformation of subgrade soils and mathematics statistics  regression methods, model forms of Tseng - Lytton model and AASHTO 2002 model  are improved and calibrated, and evaluation models for permanent deformation  of subgrade soils are recreated again.  

Permanent deformation calculation  methods of subgrade soils are studyed. Layerwise strain summation method  based on mechanical-empirical method is put forward to caltulate permanent  deformation of subgrade soils, and subgrade working zone depth calculation  formulation is used to determine calculation depth permanent deformation of  subgrade soils. Finally, using permanent deformation calculation methods of  subgrade soils, comparation of created permanent deformation evaluation  models with AASHTO 2002 evaluation model is respectively performed.

Compressive strain design index on  top of subgrade soils is researched. Compressive strain design index on top  of subgrade soils is put forward. Combined with the actual situations of  different grade highways and number of standard axle load repetitions, and  using created permanent deformation evaluation model of subgrade soils and  mul-layer elastic system calculation program BISAR3.0, permanent deformation  of  subgrade soils of different sorts of pavement stuctures is  calculated. 1.4mm is adopted to be the limit of permanent deformation of  subgrade soils. Regression formulation beteewn compressive strain on top of  subgrade soils and number of standard axle load  repetitions is built.  The created calculation formulation of compressive strain design index on top  of subgrade soils is: . On the other hand,  calculation  formulation of compressive strain design index on top of  subgrade soils under 85% guarantee rate and 95% guarantee rate are separately  given as follows : (85%) and (95%). Finally，asphalt  pavement structures design method for limiting permanent deformation of  subgrade soils is researched, and design process and design follow chart are  given.

In  the end, the problems requiring further studies are discussed.

Key Words: Asphalt  pavement, granular base, permanent deformation of subgrade soils,   repeated load triaxial test, evaluation model for permanent deformation of  subgrade soils, layerwise strain summation method, design index, compressive  strain on top of subgrade soils.