Backcalculation of subgrade stiffness under rubblised PCC slabs using multilevel FWD loads

Abstract

Rubblisation is an effective rehabilitation method for deteriorated Portland cement concrete (PCC) pavements due to its low initial costs, minimal traffic disruption and ability to minimise reflective cracking in asphalt overlays. However, the loss of strength in the PCC slab due to rubblisation creates the demand for a subgrade that is strong enough to handle traffic after rubblisation. This paper presents a research effort to develop an analysis method that allows the realistic estimation of subgrade stiffness after rubblisation from deflection measurements on intact PCC slabs before rubblisation. As a forward model, stress- and strain-dependent nonlinear subgrade models are incorporated into a finite element analysis (FEA). Based on the synthetic database generated from the FEA, different methodologies are developed to predict the coefficients in the nonlinear subgrade model from deflections under multilevel falling weight deflectometer loads.

Keywords:

• rubblisation
• FWD
• finite element analysis
• nonlinear subgrade model
• backcalculation

Acknowledgements

This material is based upon work supported by the North Carolina Department of Transportation (NCDOT) under Project No. HWY-1999-02. The authors thank NCDOT engineers in the Pavement Management Unit and Geotechnical Unit for excellent cooperation in FWD testing and laboratory soil testing.