Modeling of unsaturated granular materials in flexible pavements

Abstract

Abstract. The unsaturated granular material (UGM) is found to exhibit the moisture-sensitive and stress-dependent nonlinear cross-anisotropic behaviour in flexible pavements. This paper aims at developing a finite element (FE) model for pavement structure, which takes into account this behaviour of UGM. First, the Lytton model is employed to characterize the moisture-sensitive and stress-dependent behaviour of UGM, which incorporated a matric suction term to the existing stress-dependent constitutive model. The Lytton model is validated by the laboratory resilient modulus tests on the selected UGMs at different moisture contents. Second, the nonlinear cross-anisotropic constitutive equation of UGM is derived from the generalized Hooke's Law. The coefficients of the constitutive model are determined by the rapid triaxial test. Third, a User-Defined Material (UMAT) subroutine is developed to characterize this constitutive behaviour in the FE software ABAQUS. The UMAT subroutine adopts the secant stiffness approach with multiple damping factors. The UMAT subroutine is then implemented in the FE model of flexible pavement structures. The FE simulation results indicate the nonlinear cross-anisotropic model predicts greater pavement responses than the isotropic model. When the UGM is suction sensitive, it is found that the moisture content of UGM significantly affects the moduli distribution of base layer and the critical strains (i.e., tensile strain at the bottom of asphalt concrete, and compressive strains in base and subgrade layers) of pavement structures.

Prediction of geogrid-reinforced flexible pavement performance using artificial neural network approach

“…The finite element models were developed using the ABAQUS software to simulate the geogrid-reinforced flexible pavements (ABAQUS, 2010). represented as 8-node biquadratic homogenous solid elements with reduced integration (Gu et al 2016c). The geogrid layer was represented by a 3-node quadratic membrane element.…”

Evaluation of Carbonation Effects on Cement‐Solidified Contaminated Soil Used in Road Subgrade

“…In this paper, schematic plot of road structure is shown in Figure 2. e pavement structure is simplified as a two-dimensional (2D) axisymmetric plane strain case [44,45].…”

Mechanistic-empirical models for better consideration of subgrade and unbound layers influence on pavement performance

“… Resilient modulus models of unbound layers and subgrade 1) Empirical regression models (AASHTO 1993;ARA, 2004) 2) Nonlinear stress-dependent models (Seed et al 1967;Hicks and Monismith 1971;Thompson and Robnett 1979;Drumm, 1990;Uzan 1985;Witczak and Uzan 1988;Witczak 2003;Lade and Nelson 1987) 3) Moisture-sensitive models (AASHTO 2008) 4) Moisture-sensitive and stress-dependent models (Oloo and Fredlund 1998;Lytton et al 1993;Lytton 1995;Sahin et al 2013;Yang et al 2005;Liang et al 2008;Cary and Zapata 2011;Gupta et al 2007;Oh and Fernando 2011) 5) Stress-dependent and cross-anisotropic models (Al-Qadi et al 2010;Tutumluer and Thompson 1997) 6) Moisture-sensitive, stress-dependent, and cross-anisotropic model (Gu et al 2016a) 7) Regression models for stress-dependent model coefficients (Yau and Von Quintus 2002) 6 8) Regression models for moisture-sensitive and stress-dependent model coefficients (Gu et al 2015b)  Permanent deformation models of unbound layers and subgrade 1) Non-stress-dependent mechanistic-empirical models (Kenis 1977;Uzan 2004;Tseng and Lytton 1989;Ayres and Witczak 1998) 2) Stress-dependent mechanistic-empirical models (ARA, 2004;Uzan 2004;Korkiala-Tanttu 2009;Chow et al 2014;Gu et al 2015a) 3) Regression models for Pavement ME Design model coefficients (Tseng and Lytton 1989;ARA, 2...…”

“…IRI decreases with the increase of base modulus (Masad and Little 2004) Cross-anisotropy affects total rutting and cracking, which leads to the change of IRI (Masad and Little, 2004) High shear strength results in low IRI values (AASHTO, 2008;Chow et al, 2014) Permanent deformation of unbound base is a major distress resulting in increase of surface roughness (Zhou et al 2007) Change of IRI diminishes with increase of thickness of the base layer (Masad and Little 2004) 8 (Cary and Zapata 2011;Sahin et al 2013;Gu et al 2016a) High shear strength prevents occurrence of transverse cracking (Cleveland et al 2002;Lytton et al 2010 Resistance to loadrelated cracking would be enhanced with increase of modulus of subgrade (Gupta et al 2007;Shahji 2006;Schwartz et al 2013) N/A Lower permanent deformation of subgrade reduces the probability of load-related cracking (Oh et al 2007) Thermal…”

“…The resilient modulus model introduced herein is the one recently developed by the authors (Gu 2015c, Gu et al 2016a) for unbound base courses. It considers both nonlinear cross-anisotropic behavior and moisture-sensitive characteristics, and incorporating the proposed constitutive model into the finite element model of the base layer to quantify the influence of moisture content on the pavement performance.…”