基于等渗流速率的双层多孔沥青混合料性能优化设计

Optimal Design for Double-layered Porous Asphalt Mixture Based on an Equivalent Layer Hydraulic Velocity Approach

为明晰双层多孔沥青(Porous Asphalt,PA)路面上下各层渗流特点,为科学设计双层PA路面提供依据,从PA混合料渗流特性影响因素入手,借助自行研发、可同时测量PA混合料竖向和横向渗流能力的双向渗流速率测试仪,研究了试件空隙率、试件厚度及粒径组成的影响,并利用极限梯度提升(XGBoost)算法构建不同因素下PA混合料渗流特性影响模型,阐明各因素对渗流速率的贡献程度。同时,借助构建的渗流特性影响模型,在不改变下层厚度前提下,基于上下层层间等渗流速率原则,对遂资眉高速双层PA路面的下层空隙率进行优化,并对优化前后渗透性能和关键路用性能验证与对比。研究结果表明:横向渗流行为在PA路面渗流过程中占据至关重要的地位,试验结果显示当测试仪器直径为150 mm时,即使空隙率增至21%,横向渗流仍是主要的排水方式,并且其渗流行为较竖向渗流更稳定,受设计因素变化影响较小;其次,空隙率是影响PA混合料渗流特性的最重要因素,但试件厚度和粒径组成同样不可忽视,二者的贡献程度分别为25.2%、18.5%,因此宜在双层PA路面设计过程中充分考虑试件厚度和粒径组成的影响,结合提出的层间等渗流速率原则,可在满足渗透需求的同时实现对关键路用性能的提升。

This study investigated the layer hydraulic characteristics of a double-layered porous asphalt(PA)pavement to better determine the critical design indices.A new two-directional permeameter was developed to measure the hydraulic velocity in the horizontal and vertical directions simultaneously.Based on the permeability test results,the influences of target air void,layer thickness,and nominal maximum aggregate size(NMAS)of mixture on the hydraulic velocity were systematically studied.Subsequently,a hydraulic velocity prediction model was established based on the XGBoost algorithm,and the significance of the influencing factors to hydraulic velocity was evaluated.After that,the bottom layer of a double-layered PA pavement from Suizimei Highway was redesigned based on the established model,which achieved the equivalent hydraulic velocity between top and bottom layers and kept layer thickness unchanged.Finally,the hydraulic velocity and critical service performance of the optimized PA were evaluated.The results indicated that the hydraulic velocity in the horizontal direction played a critical role in the hydraulic characteristic of PA pavement.In this study,the hydraulic velocity in the horizontal direction was greater than that in the vertical direction,even when the target air void increased to 21%with a test sample diameter of 150 mm.In addition,the hydraulic velocity in the horizontal direction was negligibly influenced by the factors including target air void,layer thickness,and NMAS of mixture.Second,the target air void is the most significant factor affecting the overall hydraulic characteristics of the PA mixture.Moreover,the layer thickness and NMAS also affected the hydraulic velocity,contributing as much as 25.2%and 18.5%,respectively.Thus,considering the layer thickness and NMAS into the mix design can significantly decrease the target air void of the bottom layer of a double-layered PA pavement while satisfying the hydraulic demand.Thereby,this optimization approach will help improve the service performance of a double-layered PA pavement.