Validation of the subgrade shear strength parameters estimation methodology using light weight deflectometer: Numerical simulation and measured testing data

Abstract

Abstract Shear strength parameters (angle of internal friction, ϕ, and cohesion, c) of a soil medium are the key properties for the bearing capacity and stability analyses. The strength parameters have been recognized as one of the most reliable mechanical properties of pavement subgrade that can be used to estimate its permanent deformation behavior under repeated loading. In addition, when a pavement structure is subjected to a non-standard superheavy vehicle load (i.e., gross vehicle weight in excess of a few million pounds), investigation of instantaneous shear failure or onset of yielding in the pavement subgrade layer requires the knowledge of the strength parameters. Light Weight Deflectometer (LWD) has been commonly used as a Non-Destructive Test (NDT) method for in-situ determination of stiffness properties of pavement layers, unpaved roads, and subgrade layer during the construction process. In this study, the validity of a recently developed LWD-based methodology for estimating the in-situ shear strength parameters of the pavement subgrade layer has been further investigated. In this methodology, the commonly accepted hyperbolic stress-strain constitutive soil model along with the consideration of stress dependency of subgrade materials under multiple LWD load levels have been incorporated. The methodology was validated using numerically simulated LWD testing at multiple load levels for two different subgrade materials. In addition, the LWD data collected from large-scale experiments conducted at University of Nevada, Reno testing facility and National Airport Pavement Test Facility were also utilized to verify the methodology. It was found that the proposed LWD-based methodology provides a reasonable estimate for the in-situ shear strength parameters of the compacted soil subgrade.