Mechanistic-empirical pavement design guide(MEPDG):a bird's-eye view

Past editions of the American Association of State Highway and Transportation Officials （AASHTO） Guide for Design of Pavement Structures have served well for several decades; nevertheless, many serious limitations exist for their continued use as the nation＇s primary pavement design procedures. Researchers are now incorporating the latest advances in pavement design into the new Mechanistic-Empirical Pavement Design Guide （MEPDG）, developed under the National Cooperative Highway Research Program （NCHRP） 1-37A project and adopted and published by AASHTO. The MEPDG procedure offers several dramatic improvements over the current pavement design guide and presents a new paradigm in the way pavement design is performed. However, MEPDG is substantially more complex than the AASHTO Design Guide by considering the input parameters that influence pavement performance, including traffic, climate, pavement structure and material properties, and applying the principles of engineering mechanics to predict critical pavement responses. It requires significantly more input from the designer. Some of the required data are either not tracked previously or are stored in locations not familiar to designers, and many data sets need to be preprocessed for use in the MEPDG. As a result, tremendous research work has been conducted and still more challenges need to be tackled both in federal and state levels for the full implementation of MEPDG. This paper, for the first time, provides a comprehensive bird＇s eye view for the MEPDG procedure, including the evolvement of the design methodology, an overview of the design philosophy and its components, the research conducted during the development, improvement, and implementation phases, and the challenges remained and future developments directions. It is anticipated that the efforts in this paper aid in enhancing the mechanistic-empirical based pavement design for future continuous improvement to keep up with changes in trucking, materials, construction, design concepts, computers, and so on.

沥青路面JTJ014与AASHTO设计方法比较

现行JTJ014规范与AASHTO指南两种沥青路面结构设计方法是不同的体系,对两者作一定量的比较。分析和讨论表明,虽然两种结构设计方法有重要区别,但结果高度相关,区别主要体现在可靠度上。在标准排水条件下,JTJ014规范定值设计大体与AASHTO指南标准差S0=0.50、可靠度水平R=90%的结果相当;对于高速、一级公路,这个水平偏低,而对于三、四级公路可能不必要。可靠度的要求可以近似地用BZZ—100累计作用次数的倍数表达;如果需要,可以采用放大或缩小设计累计轴次的方式考虑可靠度作为过渡措施。可靠度可以在很大程度上影响路面的设计结果;研究开发反映实际情况的沥青路面可靠度标准,应当可以提到议事日程。

基于AASHTO 2002的沥青路面永久变形叠加方法研究

介绍了AASHTO 2002力学经验法设计指南中的永久变形叠加方法,在考虑应力历史、路面温度和荷载作用次数等因素的基础上,通过APA试验进行各种工况下的永久变形叠加模拟.提出以实测永久变形值与AASHTO叠加变形值之比作为AASHTO修正系数,明确了影响R主要因素包括前一个子季节的路面温度T1和永久变形D1、当前子季节的路面温度T2载作用次数N2;最终采用指数方程的形式建立了基于AASHTO 2002的永久变形叠加方程.

Multi-gene genetic programming extension of AASHTO M-E for design oflow-volume concrete pavements

The American Association of State Highway and Transportation Officials Mechanistic-Empirical Pavement DesignGuide (AASHTO M-E) offers an opportunity to design more economical and sustainable high-volume rigid pavementscompared to conventional design guidelines. It is achieved through optimizing pavement structural andthickness design under specified climate and traffic conditions using advanced M-E principles, thereby minimizingeconomic costs and environmental impact. However, the implementation of AASHTO M-E design for low-volumeconcrete pavements using AASHTOWare Pavement ME Design (Pavement ME) software is often overly conservative.This is because Pavement ME specifies the minimum design thickness of concrete slab as 152.4 mm (6 in.). Thispaper introduces a novel extension of the AASHTO M-E framework for the design of low-volume joint plain concretepavements (JPCPs) without modification of Pavement ME. It utilizes multi-gene genetic programming (MGGP)-based computational models to obtain rapid solutions for JPCP damage accumulation and long-term performanceanalyses. The developed MGGP models simulate the fatigue damage and differential energy accumulations. Thispermits the prediction of transverse cracking and joint faulting for a wide range of design input parameters and axlespectrum. The developed MGGP-based models match Pavement ME-predicted cracking and faulting for rigidpavements with conventional concrete slab thicknesses and enable rational extrapolation of performance predictionfor thinner JPCPs. This paper demonstrates how the developed computational model enables sustainable lowvolumepavement design using optimized ME solutions for Pittsburgh, PA, conditions.

AASHTO 2002无粘结材料层的回弹模量预测方法

在总结前期预测模型的基础上,AASHTO 2002设计指南建立了水—无粘结材料回弹模量预测模型。该模型作为强化综合气候模型(EICM)的重要组成部分,用来评价环境因素对公路长期性能的影响。10种公路长期性能研究(LTPP)试验路段的观测结果验证了这种预测模型的可靠性。研究结果也发现,回弹模量的季节性变化幅度(对于非霜冻影响的地区)一般是很小的,小于最初(最佳夯实)状态到平衡状态的变化幅度。介绍了无粘结材料层的长期回弹模量的计算方法,以期对我国高速公路设计与研究起到借鉴作用。

Resilient modulus prediction of soft low-plasticity Piedmont residual soil using dynamic cone penetrometer

Dynamic cone penetrometer（DCP） has been used for decades to estimate the shear strength and stiffness properties of the subgrade soils. There are several empirical correlations in the literature to predict the resilient modulus values at only a specific stress state from DCP data, corresponding to the predefined thicknesses of pavement layers（a 50 mm asphalt wearing course, a 100 mm asphalt binder course and a200 mm aggregate base course）. In this study, field-measured DCP data were utilized to estimate the resilient modulus of low-plasticity subgrade Piedmont residual soil. Piedmont residual soils are in-place weathered soils from igneous and metamorphic rocks, as opposed to transported or compacted soils.Hence the existing empirical correlations might not be applicable for these soils. An experimental program was conducted incorporating field DCP and laboratory resilient modulus tests on "undisturbed" soil specimens. The DCP tests were carried out at various locations in four test sections to evaluate subgrade stiffness variation laterally and with depth. Laboratory resilient modulus test results were analyzed in the context of the mechanistic-empirical pavement design guide（MEPDG） recommended universal constitutive model. A new approach for predicting the resilient modulus from DCP by estimating MEPDG constitutive model coefficients（k;,k;and k;） was developed through statistical analyses. The new model is capable of not only taking into account the in situ soil condition on the basis of field measurements,but also representing the resilient modulus at any stress state which addresses a limitation with existing empirical DCP models and its applicability for a specific case. Validation of the model is demonstrated by using data that were not used for model development, as well as data reported in the literature.

橡胶混凝土与普通混凝土路面路用性能预测对比

橡胶颗粒水泥混凝土由于具有较好的变形能力和韧性等优点,在道路工程中得到越来越多的重视。采用AASHTO的力学经验指南对橡胶颗粒水泥混凝土与基质水泥混凝土路面在设计年限内的使用性能进行预测。实测橡胶颗粒水泥混凝土与基质水泥混凝土的抗折强度、弯拉模量作为输入参数,气候模型采用与中国北方气候相近的明尼苏达州气候模型。通过对两种混凝土路面使用性能预测可知:橡胶混凝土路面在使用的过程中,其平整度、断板率、错台、累积损伤均小于基质混凝土路面。因此,在荷载与气候的作用下,橡胶混凝土路面的使用性能优于基质混凝土路面。

Sensitivity analysis of longitudinal cracking on asphalt pavement using MEPDG in permafrost region

Longitudinal cracking is one of the most important distresses of asphalt pavement in permafrost regions. The sensitivity analysis of design parameters for asphalt pavement can be used to study the influence of every parameter on longitudinal cracking, which can help optimizing the design of the pavement structure. In this study, 20 test sections of Qinghai-Tibet Highway were selected to conduct the sensitivity analysis of longi- tudinal cracking on material parameter based on Mechanistic-Empirical Pavement Design Guide （MEPDG） and single factorial sensitivity analysis method. Some computer aided engineering （CAE） simulation techniques, such as the Latin hypercube sampling （LHS） technique and the multiple regression analysis are used as auxiliary means. Finally, the sensitivity spectrum of material parameter on longitudinal cracking was established. The result shows the multiple regression analysis can be used to determine the remarkable influence factor more efficiently and to process the qualitative analysis when applying the MEPDG software in sensitivity analysis of longitudinal cracking in permafrost regions. The effect weights of the three parameters on longitudinal cracking in descending order are air void, effective binder content and PG grade. The influence of air void on top layer is bigger than that on middle layer and bottom layer. The influence of effective asphalt content on top layer is bigger than that on middle layer and bottom layer, and the influence of bottom layer is slightly bigger than middle layer. The accumulated value of longitudinal cracking on middle layer and bottom layer in the design life would begin to increase when the design temperature of PG grade increased.