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80 need for additional laboratory-based studies for validation, requirements of stress analysis, and other factors. Most of the assessments noted in these tables are based on the technical information available to the author, and because it is subjective, these assessments should be consid- ered as suggestive assessments. Resilient Moduli Magnitudes A summary of moduli of various bases and subgrade mate- rials is presented in this section. The moduli ranges from study to study are different, and these variations are attrib- uted to material and sampling differences as well as to test procedure and equipment variations. Because it is not prac- tical to summarize this information in this synthesis, some of the moduli information from a few studies (including one from an LTPP study) is presented in Appendix D. FIGURE 86  Comparisons between measured and predicted moduli of fine grained soils (Titi et al. 2006). The recommended approach to determine the resilient moduli of soils is to test and measure the moduli of subgrade Table 19 Comprehensive Assessments of Various Methods for Determining Resilient Properties—Part I Subgrades Relationship with Design Skillled Unbound MR (nature of Is this Method Personnel Time to Perform Cost Method Clayey Sandy Bases correlations) Standardized? Required? (quick/long) (relative) Y (direct, Lab—RLT Y Y Y Y Y Long High Level 1) Lab—Resonant N (indirect, Y Y Y needs Y Y Long Moderate Column Poisson’s ratio) Lab—Others N, indirect Low to Y Y Y Y N Quick (CBR, R) (Level 2) Moderate N, direct Low to Field—FWD Y Y Y N Y Quick (Level 1/2) Moderate N, indirect Low to Field—Geogauge Y Y Y N N Quick (Level 2) Moderate N, indirect Low to Field—PSA Y Y Y N N Quick (Level 2) Moderate N, direct Field—LFWD Y Y Y N N Quick Low (Level 1/2) N, indirect Field—DCP Y Y N Y N Quick Low (Level 2) Moderate Field—CPT Y Y N N, indirect; R N Y Quick to High Note: Y = yes; N = no; R = needs more research.

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 81 Table 20 Comprehensive Assessments of MR Prediction Models Applicable Needs Stress Additional Estimation Need Laboratory in the More Unbound Studies for Bases and Data and Model Type Subgrade Bases Repeatability Reliability Verification? Subgrades Research? Direct Correlations Based on Moderately Y Y Y Y Not Needed Y Laboratory Determined Parameters Reliable Direct Correlations Based on Field Moderately Y Y Y Y Not Needed Y, R Determined Parameters Reliable Low to Indirect Correlation Parameters—​ Y Y Y Moderately Y Needed Y 2 Model Constants Reliable Moderately Indirect Correlation Parameters—​ Y Y Y to Highly Y Needed Y, R 3 Model Constants Reliable Note: Y = yes; N = no; R = needs more research. Table 21 Comprehensive Assessment of Various Methods for Determining Resilient Properties—Part II Applicable Applicable in Non- in New Applicable QC/QA for Destructive Needs Additional Sampling Pavement in Pavement Base/Subgrade Nature of Correlations Lab Studies for Method Needed? Construction? Rehabilitation? Compaction? Testing? Type? Verification? Lab—RLT Y Y Y N Y Semi-empirical N Lab—Resonant Y Y Y N Y NA N Column Lab—Others Y Y Y N N Empirical Y (CBR, R) Theoretical Y (validation of Field—FWD N Y Y Y Y (back­ backcalculated calculated) moduli) Theoretical Y (validation of Field— N Y Y Y Y (back­ interpreted Geogauge calculated) moduli) Theoretical Y (validation of Field—PSA N Y Y Y Y (back­ interpreted calculated) moduli) Theoretical Y (validation of Field—LFWD N Y Y Y Y (back­ interpreted calculated) moduli) Y (validation of Field—DCP N Y Y Y N Empirical interpreted moduli) Semi- Y (validation of Field—CPT N Y Y Y N empirical to interpreted empirical moduli) Note: Y = yes; N = no; NA = not applicable; R = needs more research.