Numerical Method of Flexible Pavement considering Moisture and Stress Sensitivity of Subgrade Soils

Abstract

Weaknesses of the subgrade structure induce the asphalt surface diseases and shorten the service life of flexible pavement. However, the resilient modulus (Mr) of subgrade soils is difficult to be evaluated directly since the subgrade is hidden and covered by the granular or asphalt layer. This study aimed to establish a numerical approach to predict the dynamic behavior of flexible pavements considering the stress sensitivity and moisture variation of subgrade soils. Firstly, 2D FEM simulations of flexible pavements were performed with half-sine loadings. A constitutive model of subgrade soils was proposed to incorporate soil suction and octahedral shear stress. It was validated using the laboratory triaxial test data of 3 selected soils. Then, the developed model was programmed by the user-defined material subroutine (UMAT) in the software ABAQUS. Subsequently, the validity of FEM model was verified by the laboratory tank model. Finally, the effect of moisture contents on the dynamic response of pavement structures was studied by tensile stress and vertical compressive strain. Results show that the surface deflection of the FEM model is similar to that of the actual pavement structure with the R2 of 98.44%. The developed UMAT program is reliable since the distribution of Mr in the FEM model is influenced by the stress and moisture condition of subgrade soils. When the moisture content is increased by 63%, the average Mr of subgrade soils is decreased by 18.7%. Meanwhile, the stiffness softening of subgrade soils increases vertical compressive strain at the top of the subgrade and the tensile stress at the bottom of the surface layer. It is interesting that the developed model can be applied to analyze the fatigue cracking of both subgrade and surface layers in the future.

Calculation and Control Methods for Equivalent Resilient Modulus of Subgrade Based on Nonuniform Distribution of Stress

“…Many researches have studied the nonlinear convergence of the elastic modulus. e tangent stiffness method was applied to solve the nonlinear stress-strain behaviour by updating the tangent stiffness at each iteration until the stress increment converges [1]. Young's modulus E (Young's modulus is equal to the resilient modulus in a pure elastomer) in equation (8) is replaced by M ir corresponding to each node to obtain a new modulus of each node.…”

“…e resilient modulus of all pavement layers, including subgrades, is one of the primary material properties as it is used in mechanistic pavement thickness design [1]. e resilient modulus (M r ) is widely applied and defined as the slope between the largest resilient strain and the largest deviatoric stress of dynamic triaxial tests [2].…”

“…However, many previous studies have also proved that the prediction model of resilient modulus of subgrade soil is highly dependent on stress states [18,19]. e most famous prediction model of resilient modulus of subgrade is the three-parameter model proposed by Lytton, as shown in equation (1), which is ultimately included in the Mechanistic-Empirical Pavement Design Guide (MEPDG) [8]. Because of different stress states inside the subgrade, the M r of subgrade soil is different at different points inside the subgrade structure.…”

Train Moving Load‐Induced Vertical Superimposed Stress at Ballasted Railway Tracks

“…As a result, the trapezoidal method significantly overestimated the vertical stress in comparison with the field measurement [5,8]. In addition, the ballast aggregates subjected to the cycle train loading, resulting in considerable ballast fouling, such as particle degradation, infiltration of fines from surface, subballast and subgrade infiltration, and weathering factors [2,3,[9][10][11][12][13][14][15][16][17][18][19][20][21]. erefore, the properties of ballast (the internal friction angle of ballast (φ B ) and maximum particle size (D max )) and stress distribution in substructure significantly varied with the real situations in practice [22][23][24].…”

Combined Effect of Compaction Methods and Loading Conditions on the Deformation Behaviour of Unbound Granular Material

“…It is well known that flexible pavements with composite bases have desirable structural and functional capacities [1][2][3]. Unbound granular material (e.g., graded crushed stone) is an important construction material used in the base and subbase layers of flexible pavement; its advantages include the ability to provide structural support for asphalt concrete layers and an adequate response to traffic loads at a relatively low cost [4][5][6]. e fatigue cracking and rutting development of asphalt concrete layers are associated with the deformation characteristics of unbound granular material layers [7,8]; these characteristics are predicted and controlled typically during pavement design [9,10].…”