Method to estimate design resilient modulus (Mr) of unbound materials for rehabilitation in M−E design

•Mr values of the unbound materials are crucial for mechanistic pavement design.•Selecting a design Mr value for a stress dependent material is challenging.•Laboratory-measured Mr values for base and borrow materials fit Theta model well.•Laboratory-measured Mr values for subgrade soils fit Uzan and Universal model well.•Innovative approach to estimate the design Mr for pavement rehabilitation. The resilient moduli (Mr) of the unbound layers and subgrade (SG) soils play a major role in estimating the pavement responses and analyses for mechanistic-empirical (M−E) pavement design. Most of the analysis procedures require a single representative Mr value for each unbound layer. However, estimating one representative values for each unbound layer is difficult as it depends on the state of the stresses within the layer. In this study, the stepwise mechanistic analysis approach is used for determining representative Mr values for the unbound materials typically used in Nevada. The Nevada Department of Transportation (NDOT) uses mainly three types of unbound material in the pavement structure; crushed aggregate base (CAB), borrow material, and SG soils. The unbound materials were sampled from multiple locations throughout Nevada District 1 and evaluated through several laboratory tests, which include sieve analysis, moisture-density relationships, and resilient modulus. The resilient modulus values for unbound material at multiple states of stresses were measured in accordance with AASHTO T307. The measured resilient modulus values were fitted to multiple constitutive models to assess the suitability of the models. The CAB and borrow materials fit the theta model very well while the SG soils fits the Uzman model and universal model. The ILLI-PAVE 2005 finite element (FE) program was employed for computing stresses as well as deflection basins in typical conventional flexible pavements under a representative tire loading. The calculated deflection basin was used for estimating the Mr values of the unbound layers using MODULUS 6.1 software.