Proposed Enhancements to Pavement ME Design: Improved Consideration of the Influence of Subgrade and Unbound Layers on Pavement Performance (2019) / Chapter Skim
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Pages 97-125
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From page 97... ...
97 CHAPTER 5. INTERPRETATIONS, APPRAISAL, AND APPLICATIONS INTRODUCTION This project developed several models as described in previous chapters for unbound granular materials and subgrade, which are intended to enhance the sensitivity of predicted pavement performance to these underlying layers.
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98 FWD tests (205)
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101 Table 25. Material Parameters of Pavement Layers.
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102 in which, for the bottom-up cracking: 1 (11.02 3.49h )
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103 v is the average vertical strain in the layer/sublayer as obtained from the primary response model. h is the thickness of layer/sublayer, in; 1a =0.15; 9a =20.0; 1b =0; 9b =0.
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104 COMPARISONS OF PROPOSED MODELS AND PAVEMENT ME DESIGN MODELS Before the sensitivity analysis, several cases are run to check the nonlinearity and anisotropy of the base layer in the pavement model. Different from most of current simulations that treat the subgrade as a linear elastic material, the pavement models with moisture-sensitive subgrade are shown in the following three sections.
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From page 107... ...
107 unbound base layer proposed by the Pavement ME Design Guide and researchers were compared. Comparison of Resilient Modulus Models for Unbound Granular Base The validation of the proposed model and comparison between the proposed model and the model in the Pavement ME Design were presented in previous studies (213, 214)
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108 SENSITIVITY ANALYSIS OF PROPOSED MODELS AND PAVEMENT ME DESIGN MODELS The sensitivity analyses were performed on the FE models with the proposed base/subgrade models to determine the effects of the load level, pavement structure, material properties, and moisture conditions on the pavement performance, in which the rutting model is the proposed rutting model. Different Loading Levels Figure 62 presents the pavement performance under different loading levels as computed with the COMSOL using models developed by researchers.
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109 Different Thicknesses of the Asphalt Layer Figure 63 presents the pavement performance when using stresses and strains as computed with COMSOL and material models developed by researchers and when the thickness of the asphalt layer varies. Based on the Eqs.
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110 of the base layer varies. As the thickness of the base layer increases, the tensile strain at the bottom of the asphalt layer decreases, which reduces the load repetitions to the fatigue cracking.
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112 Figure 66. Pavement Structure for LTPP Section 1-3028.
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114 Thickness of Base Layer Figure 69 shows the sensitivity of the thickness of the base layer on the development of faulting based on both the first and the second faulting models. From Figure 69a, it seems that the effect of the thickness of the base layer has slight impact on development of faulting.
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116 Effect of Climatic Zone Figure 72 shows the development of faulting in different climate zones. The faulting develops faster and greatest in the WF climatic zone and accumulates slowest and lowest in the DF climate zone from Figure 72a but in WNF climate zone from Figure 72b.
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117 Table 28. Selected LTPP Pavement Sections and FWD Backcalculated Modulus Values for Each Layer.
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118 Table 29. Calculated MR Values at the Mid-depth of Base Layer at Different Moisture Conditions.
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121 Figure 74 compares the sensitivity of moisture on k-value using the ANN model and Pavement ME Design model. Pavement ME Design has almost no sensitivity of moisture on subgrade k-value.
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122 ANN model Pavement ME Design (a) ANN model Pavement ME Design (b)
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123 ANN model Pavement ME Design (c) Figure 75.
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124 ANN model Pavement ME Design (a) ANN model Pavement ME Design (b)
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125 ANN model Pavement ME Design (c) Figure 76.
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