Evaluating base widening methods

Pavement widening can increase roadway capacity and improve safety, but results in a longitudinal joint between the existing and widened section that is susceptible to longitudinal pavement cracking. Previous research on construction methods focused on the pavement layer but this research looks at the effects of joint type on the base layer. Two base widening joint types, vertical and tapered, are commonly implemented by the Wyoming Department of Transportation. The objective of this study is to determine the most suitable base widening technique for durable pavement sections resistant to longitudinal cracking along the joint line. Field and laboratory evaluations were carried out on 28 existing pavement widening projects to determine the strength of the base layer as well as the occurrence and severity of longitudinal cracking. Results indicate that the tapered joint type has better strength in terms of the Dynamic Cone Penetrometer and Falling Weight Deflectometer analyses, less longitudinal cracking, and lower cost.     

Estimating fatigue endurance limits of flexible airfield pavements

In perpetual pavements, damage from bottom-up cracking can be limited to the top surface lift through using a very thick surface layer or a binder-rich intermediate layer. This can be attained by maintaining tensile strains at the bottom of the hot-mix asphalt (HMA) layer below a certain value known as the fatigue endurance limit (FEL). This paper presents a method for estimating a strain-based FEL for flexible airfield pavements. The proposed method is based on the concept that a 50% reduction in HMA layer modulus would indicate initiation of fatigue cracking. Falling weight deflectometer (FWD) testing results, collected from National Airport Pavement Test Facility (NAPTF) flexible pavement sections, were analyzed to determine at which loading pass each section had a 50% reduction in HMA layer modulus (N_f50). NAPTF tensile strain data were also used to determine the tensile strain at N_f50 for each pavement section by averaging the peak tensile strains. The proposed approach was validated by comparing its results to those obtained using a common FEL estimation model known as the rate of dissipated energy change (RDEC) model. To further verify the results of the proposed approach, peak tensile strain was plotted vs. number of loading cycles for all sensors. Using these plots, the peak tensile strain at which the variability in the strain gauge data increased was used as an estimate of a possible FEL. The N_f50 tensile strains estimated using the proposed method were comparable to the values determined from RDEC and variability approaches.     

Multi-level backcalculation algorithm for robust determination of pavement layers parameters

The backcalculation procedure applied to a mechanical characterization of the road pavement is usually limited to an identification of the elastic modulus of each layer only. The remaining parameters of the model are usually set as known, while performing an inverse analysis. Among assumed parameters are thicknesses of the model layers and frequently considered as constants on a homogeneous section of the road. This is an obvious simplification, because sections in general are inhomogeneous, i.e. the thickness of each layer changes slightly along each road section. Thus the precise and possibly nondestructive estimation of the layers thicknesses is very important and crucial in the inverse procedure. Here, a hybrid form of the optimization algorithm, where the condition of a constant thickness does not need to be fulfilled is described. Further on, the objective function is formed as a discrepancy between reference and computed deflection derivative instead of a deflection curve. In consequence, the values of backcalculated parameters are several per cent more precise compared to a standard procedure. Whenever the thickness of the asphalt layer of the pavement structure cannot be assumed a priori as a constant, the proposed here method appears to be necessary if one does not want to perform costly and destructive in situ drilling tests.     

粘弹性地基上多块板的动力时域反分析方法

本文针对具有接缝传荷的多块板动力反问题,提出一种在时域内解决的方法。首先 应用有限元方法对多块板进行离散,并将地基简化为由弹簧和阻尼器组成的粘弹性地基,成 功地分析了粘弹性地基上多块板的动力问题［５］．进而根据系统识别方法,对落锤式弯沉仪（ＦＷＤ） 传感器所记录的时程曲线进行反演分析来确定结构参数。数值计算结果表明,该方法具有较 好的稳定性和收敛性。可以广泛应用于以落锤式弯沉仪（ＦＷＤ）为检测工具的混凝土路面上, 从而为进一步研究刚性路面的无损检测和承载力评价提供了技术基础。