Development of methodology to include the strength contribution of select subgade materials in pavement structure

Abstract

This study was conducted to develop a methodology to incorporate the structural contribution of working platforms, including those constructed with industrial by-products, into the design of flexible pavements. Structural contribution of the working platform was quantified in terms of a structural number or an effective roadbed modulus. Resilient modulus obtained from large-scale model experiments(LSME) conducted on several working platform materials (i.e., crushed stone (referred to as ?breaker run?, Grade 2 granular backfill (referred to as Grade 2), foundry slag, foundry sand, and bottom ash) were used in the analysis. Design charts are presented that show the structural number or the roadbed modulus as a function of type of material and thickness of the working platform. Another study was conducted to evaluate the structural contribution of geosynthetic-reinforced granular layers that are used as working platforms to the pavement structure. Based on the LSME and from the field Falling Weight Deflectometer (FWD) tests, the relationship between back-calculated elastic modulus and bulk stress was obtained. The improvement in layer coefficients is rather small for the nonwoven geotextile and drainage geocomposite (10%) and somewhat higher for the geogrid (40%) and for the woven geotextile (18%) in a 0.30-m thick granular working platform layer (treated as a subbase). The contribution of geosynthetics would be even less having a thicker subbase layer.