破损状态下沥青路面结构层状况

评价方法研究

Research  on Evaluation Method of Asphalt Pavement

Structure  Layer under Damaged Condition

研究生：谢兆星

指导教师：郭忠印、丛林

二○○九年七月

摘要

随着时间的推移，早期修建的部分半刚性基层沥青路面在交通荷载的重复作用和气候、环境等自然因素影响下，逐步出现开裂、松散和沉陷等损坏现象，承载能力逐渐下降，路面相继进入了维修阶段。在对旧沥青路面维修过程中，如何准确地对破损状态下的沥青路面结构层状况进行评价是业主和设计单位面临的首要问题。落锤式弯沉仪(Falling Weight  Deflectormeter,简称FWD)作为无损检测设备，以其准确、快速、方便、信息量大和可模拟实际行车荷载作用等优点得到世界各国的广泛使用，基于FWI)弯沉盆的路面结构层模量反分析已经成为公路界所关注的研究热点。然而目前国内外流行的反分析软件大多是以静态多层弹性体模型为基础的，忽略了动力荷载路面结构响应的影响，另外，大多反算软件的路面模型为理想的完好路面(多层连续弹性体系)，但在实际FWD检测过程中旧沥青路表面经常存在诸多病害，如何对破损路面进行合理的评价是目前急需解决的问题。

针对以上问题，本文在国内外研究基础之上，通过资料调研、动力学计算、统计分析和现场FWD检测等技术手段，充分利用FWD弯沉盆内包含的路面特征信息，对破损状态下沥青路面结构层状况评价进行深入研究，具体研究成果如下：

（1）通过资料调研和现场路况调查，对半刚性基层沥青路面主要的结构性破损形式进行了归纳总结；对破损路面的FWD弯沉盆数据和反算结果进行分析，结果表明路面破损将导致弯沉盆不规则和反算模量变异性增大。

（2）通过动力有限元模型，对路面结构的动力特性以及动力效应对拟静力模量反算的影响进行分析，分析结果表明，路面在动态荷载作用下，计算出的路面弯沉值明显小于静力荷载作用下的弯沉值；位移响应曲线滞后于荷载，测点距荷载越远，滞后越明显；利用静态反分析方法对动态弯沉盆分析时，反算模量误差明显增大，动力效应对模量反算结果影响明显，采用动力反分析方法对实测弯沉盆进行分析是十分必要的。

（3）通过动力有限元计算不同路面组合的路表弯沉盆，选择弯沉盆参数指标并对参数指标与结构层模量的相关性进行分析，根据相关性分析结果构建路面各结构层模量预测方法。分析结果表明，土基模量可以通过曲率指标CI₇和形状指标F₈确定，面层和中间层的模量可以通过回归模型进行预测。通过理论和实测FWD检测数据对各结构层和土基模量预测方法进行验证，结果表明，在理论数据下预测方法具有较高的预测精度，但计算的弯沉盆与现场实测弯沉盆之间的均方误差较大，预测结果并不太理想。

针对上述方法的不足，将得到的结构层模量值作为初始值利用迭代试算法进行动力反分析。分析结果表明，迭代试算法得到的理论动态弯沉盆与实测弯沉盆比较接近，精度基本上满足工程要求；通过改进的迭代试算法得到的面层和土基模量与回归模型得到的模量值差别不大，而中间层模量相差较大，表明面层和土基模量预测方法是可靠的；基于迭代试算法的动力反分析结果比静力反分析更接近于路面实际状况，可以避免静力反分析所出现的不合理现象。

（4）通过动力有限元模型，分析了典型结构性破损(开裂、层间滑移、基层松散等)对路面弯沉盆和预测模量的影响。研究结果表明，路面破损将导致路面弯沉值增大和弯沉简形状的不连续；当路面结构层存在破损时，无论是动力反分析还是静力反分析，预测模量的误差都会增大，对路面结构层状况评价可能出现误判。例如，当面层与基层间存在不连续接触时，中间层的模量被严重低估。基于此，本文提出利用等效损伤模量评价破损路面状况一根据路面结构层的破损状况选取结构层等效损伤模量，同时提出损坏状态判别指标：曲率指标和表面模量指标，并给出了相应的判定标准。

（5）提出了破损状态下路面结构层状况评价方法，依托实体工程对该方法进行了验证；针对嘉浏高速公路大修工程，提出了土基和中间层处治的判定指标和标准，并利用处治标准对土基和中间层进行了段落划分。

关键词：沥青路面；半刚性基层；破损；FWD；动力响应分析；弯沉盆参数；模量反分析；有效模量；结构层状况；评价方法

ABSTRACT

The pavement layer condition  estimation is particularly important for determining rehabilitation  strategies．The Falling weight  Deflectometer (FWD) is popularly used for the evaluation of the pavement  condition because the FWD test is accurate，quick to  perform，and simulates actual  traffic load closely．Using backcalculation  programs used to analyze the FWD deflections，the  structural condition of the pavement system call be determined quickly．However, there  are many deficiencies in these backcalculation programs．For example，these  programs are based 011 static analysis without taking into account the  dynamic effects of the FWD test．On the  other hand，these programs are  developed within the framework of the muti—layered continuous elastic theory,  but the FWD tests are often performed on damaged pavements．The paper  seeks to improve the ability of assessing pavement condition by introducing  dynamic analysis and the effects of distresses of FWD tests．The major  efforts are presented below．

(1)It is discovered that the  asphalt pavement layers are cracked and／or debounded  and／or broken when rehabilitation is  required．The FWD deflection basins may  show unusual shapes and the backcalculated moduli may be unreasonable when  the FWD tests are performed over distressed areas．

(2)The dynamic behavior of asphalt  pavement during FWD testing and the dynamic effects on results of static  back--analysis are investigated．The dynamic  deflections are lower than static deflections when the depth of rigid layer  is fixed to infinity．There is a significant lag  between the peak of the applied FWD load and sensor deflections．The dynamic  effects on results of conventional static backcalculation procedure are  significant．It is necessary to account  for the dynamic effects in performing the analysis of moduli backcalculation．

(3)A dynamic finite element program  is developed to generate the synthetic deflection database．Using the  synthetic database from dynamic，linear  elastic analysis，the sensitivity between  deflection basin parameters and layer moduli is analyzed and the predict  methods of layer moduli age established．The  subgrade modulus Can be determined by the two deflection basin parameters，Curvature  Index C1₇ and Shape Factor F₈．The AC  layer modulus and the middle layer modulus can be estimated by regression  equations．Theoretical and field data  are used to validate the proposed procedures．Results  indicate that the better estimation of the layer moduli can be achieved under  theoretical data，but the good agreement is  not found between in-situ measured and computed basins．Based on  the above problem，an improved iterative  method is proposed．Field FWD measurements age  analyzed by the iterative method and by the SIDMOD program．Results  show that the predicted layer moduli from the iterative method are more  reasonable．

(4)Effects of distresses in the  pavement layer on FWD deflections basins and predicted layer moduli are studied  by the finite element method．When  distresses exist，the value of deflection  increases and the shape of FWD deflection basins may be discontinuous．When the  FWD tests are performed over distressed areas，the  predictive precisions are lower and backcalculated moduli may be surprising．For example，when there  is a debounding between AC and middle layer, the middle layer modulus may be  underestimated．Based on this problem，the  effective moduli method of damaged layer is presented and indicators as well  as criteria to detect whether the layer is intact or damaged are proposed．

(5)The evaluation method of  distressed asphalt pavement layer condition is proposed．Field FWD  measurements are analyzed by the proposed method．Result reveals  the predicted layer moduli from dynamic back--analysis for intact pavement better  agrees with the actual pavement conditions and the effective moduli to  estimate damaged layer is more reasonable．

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

Keywords：asphalt  pavements，semi-rigid base，distress，Falling  Weight Deflectometer, deflection basin parameters，dynamic  response analysis，moduli backcalculation，effective  moduli，layer condition，evaluation  method