Evaluating Mechanical Properties of Earth Material During Intelligent Compaction (2020) / Chapter Skim
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27 Findings from Numerical Model Introduction This chapter presents the development of a 3D FE model simulating the roller compaction of one- and two-layer geosystems. Different levels of complexity were considered in the model, including the use of linear and nonlinear geomaterial approaches and simulations of the roller operation ranging from a static load to a stationary vibratory load to moving vibratory loads.
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28 Evaluating Mechanical Properties of Earth Material During Intelligent Compaction Typical values used for the simulated drum are shown in Table 3-1. The vibratory motion of the roller was maintained for 200 ms, equivalent to six load cycles.
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Findings from Numerical Model 29 This model was incorporated as a user defined material subroutine into LS-DYNA to account for the nonlinear behaviors of geomaterials under loading conditions. Mazari et al.
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30 Evaluating Mechanical Properties of Earth Material During Intelligent Compaction The research team considered six levels of sophistication of the FE model, as described in Table 3-3. In terms of the surface displacements and stresses at critical points, the geosystem responses were obtained directly under the drum of single- and two-layer geosystems simulating the drum as static and vibratory.
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Findings from Numerical Model 31 where Y ′i = the estimated displacement obtained from the linear equation of the fitted trend, Yi = the displacement from the FE simulation, and n = the total number of points. In general, displacement pairs correlated with R2 values greater than 0.85 and typically greater than 0.90, while normalized errors of estimate were typically less than 0.20.
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32 Evaluating Mechanical Properties of Earth Material During Intelligent Compaction on the analysis time and the relationships between all the models are described in detail in Appendix D, which is available as part of the downloadable "Appendices.pdf" file on the NCHRP Research Report 933 webpage)
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Findings from Numerical Model 33 material nonlinearity on the depth of influence was more significant in single-layer geosystems than in two-layer geosystems. This was also reflected in the standard deviation values of the depths of influence shown in Table 3-5, where higher standard deviations occurred in singlelayer systems as well.
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34 Evaluating Mechanical Properties of Earth Material During Intelligent Compaction models were also taken into consideration. Table 3-6 shows that subgrade nonlinear parameters k ′1 (related to stiffness)
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Findings from Numerical Model 35 roller's operating features (e.g., operating weight and dimensions of the drum) on the pavement responses should be taken into consideration.
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36 Evaluating Mechanical Properties of Earth Material During Intelligent Compaction led to an increase in the surface displacement, with a factor of 2.17 and 2.00 for single-layer and two-layer geosystems, respectively. Like the surface displacements, the surface vertical stresses directly under the drum increased by about a factor of two when the magnitude of the imposed weight increased by a factor of two.
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Findings from Numerical Model 37 Evaluation of Approaches for Developing Forward Models The traditional methods for modeling and optimizing complex drum-soil compaction systems require huge amounts of computational resources. For this reason, a simplified model is necessary to predict the pavement responses with minimal computational effort and reasonable accuracy.
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38 Evaluating Mechanical Properties of Earth Material During Intelligent Compaction where C1 = 0.00425, C2 = 0.0139, C3 = 205, C4 = 0.075, C5 = 5.58 × 10–6, C6 = 2.98 × 10–10, C7 = 0.0004, C8 = 4.65 × 10–5, and y = the operating index (as defined in Equation 3-5)
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Findings from Numerical Model 39 Stiffness Stiffness is defined as the resistance to deformation of a material under an applied load. As such, stiffness is not a unique material property; rather, it is the response of the pavement system to the load.
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40 Evaluating Mechanical Properties of Earth Material During Intelligent Compaction For the prediction of stiffness for single-layer geosystems, Equation 3.8 reduces to: , (3-9)
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