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8 Introduction Problem Statement The primary tool currently used for quality management of earthwork and unbound aggre- gates is a nuclear density gauge (NDG) to ensure appropriate density and moisture content. With the emphasis on the mechanistic-empirical (ME) pavement design procedures in the last decade, significant research effort has been devoted to understanding and implement- ing modulus-based quality control of compacted geomaterials (e.g., Von Quintus et al. 2009; Tutumluer 2013; Nazzal 2014). Nazarian et al. (2014) systematically enumerated the technical and institutional complications related to incorporating modulus-based spot-testing devices such as the light weight deflectometer (LWD) and provided practical solutions to some of them. These complications included (1) relating the design parameters to the construction quality control parameters, (2) incorporating the impact of moisture content on the measured modulus, and (3) developing field-calibrated numerical models that can be used in the proper evaluation and acceptance of the compacted geomaterials. Many of those complications are directly applicable to the implementation of the IC systems. If implemented properly, the IC technology can provide quality control over 100% of the compacted geomaterials (a major shortcoming of the spot testing). Furthermore, the uniformity of the compaction process can be assessed realistically with IC measurement values (ICMVs). Despite the tremendous efforts to investigate the application of the IC technology in the construction quality control, knowledge gaps remain that prevent it from being used for quality acceptance. These gaps include: ⢠Lack of a robust and practical methodology to determine the lift-specific target ICMV (ICMVTarget) with the consideration of moisture content, and ⢠Absence of a rational means of relating the different proprietary ICMVs reported by different roller vendors. A realistic numerical model for a roller-soil system can be combined with a state-of-the-art inverse algorithm to provide layer-specific ICMVs for quality control and potentially for the quality acceptance. Objective The main objective of this research was to develop procedure(s) to estimate the mechanical properties of the geomaterials using the IC technology. The final process needed to be robust and practice-ready so that departments of transportation (DOTs) and state highway agencies (SHAs) can readily incorporate it in their IC specifications. Figure 1-1 illustrates the process followed by the research team to achieve this objective. During the course of the project, C H A P T E R 1
Introduction 9 the flowchart acted as a living document and was updated as warranted by the results of the experimental and numerical studies. Organization of Report The study has been divided into three phases. Phase 1 (Documentation) covered the following topics: ⢠Compilation of literature and current IC specifications; ⢠Documentation of fundamental, technological and practical limitations of IC technology; ⢠Improvement of numerical models and conduction of sensitivity analyses; ⢠Development of algorithms to estimate target ICMV that are based on mechanical properties; ⢠Recommendation of the proper way to incorporate the variations in moisture content in the process; ⢠Recommendation of the most appropriate QC/QA process; and ⢠Conduction of field evaluation to calibrate the FE models and to verify the processes for estimating ICMVs and mechanical properties for a wide variety of fine- and coarse-grained geomaterials. These topics are summarized in Chapter 2. The five primary tasks associated with Phase 2 consisted of: 1. Addressing Practical Issues, 2. Developing a Forward Model, Select Material Type for All Layers Simulate Roller Measurements ⢠Determine Target Field Measurements Value (ICMVTarget) for each Layer ⢠Determine Target NDT Value (optional) Estimate Properties of All Layers ⢠Physical: Thickness ⢠Index: Gradation and Atterberg Limits ⢠Mechanical: Resilient Modulus Parameters, Strength ⢠Moisture-Density: In Situ, OMC Select Roller Parameters ⢠Model: Drum Dimensions and Weight ⢠Vibration Parameters: Amplitude, Frequency, Speed Pre-Map Layer of Interest ⢠Extract Statistical Information about ICMV ⢠Conduct Spot Test with Modulus-based NDT Devices (to Extract Layer Modulus) Map Compacted Layer ⢠Extract Statistical Information about ICMV and âICMV ⢠Provide Average Stiffness and Uncertainty Related to Estimated Properties Post-Processing to Extract Layer Mechanical Properties ⢠Conduct Spot Test with Modulus-based NDT Devices ⢠Conduct Tests to Characterize Moisture Variation ⢠Use a Robust Inverse Algorithm to Extract Modulus Perform Compaction to Achieve Target ⢠Review ICMV Color-Coded Map to Ensure DOT Acceptance Figure 1-1. Implementing roller IC technology (generic flowchart).
10 Evaluating Mechanical Properties of Earth Material During Intelligent Compaction 3. Developing an Inverse Algorithm, 4. Calibrating and Validating Models, and 5. Implementation Plan of Proposed IC. Phase 2 consisted of a systematic research effort to establish field processes and analysis algorithms considering the following attributes for diverse range of geomaterials: ⢠The most relevant parameters that should be considered, ⢠Their practical and desirable tolerances, ⢠A means of rapidly measuring output parameters, and ⢠A means of analyzing the field results in a rapid and robust manner that balances the risks of highway agencies and the contractors. The outcomes of this phase were generic specifications and a work plan to evaluate and validate their different options. Phase 3 consisted of the evaluation of the practicality of the methods and validation and fine-tuning of the proposed algorithms and test methods that had been developed in Phase 2. Field tests were performed to validate the robustness and practicality of the proposed specifica- tions. Phase 3 also included summarizing the research and field activities into this final report and draft construction specifications for compaction of geomaterials with IC and extracting layer properties. The proposed specifications are presented in Appendix A of this report. To keep this report as concise as possible, each chapter presents a summary of the relevant information, with more extensive information and analysis presented in the appendices. Depending on familiarity or interest, the reader can review the summary and then proceed to the referred appendices for more in-depth information. Specifically, ⢠Chapter 2 briefly describes the fundamentals of IC measuring systems and summarizes the state of knowledge in the areas of IC and current IC specifications. ⢠Chapter 3 summarizes the findings from the numerical modeling of roller compaction of geomaterials and assembly of a comprehensive databases of pavement responses of various pavement structures and layer properties subjected to IC roller compaction during mapping operations. ⢠Chapter 4 summarizes field test activities conducted at sites in Texas and the MnRoad facility in Minnesota, and features the information collected from both the field measure- ments and laboratory testing. Data obtained from laboratory and field activities is used to develop appropriate transfer functions. ⢠Chapter 5 contains information about the evaluation and calibration of the forward models using measured field data. ⢠Chapter 6 discusses the development, calibration and evaluation of the inverse models for extracting the mechanical properties. This chapter also proposes preliminary adjustment factors that can be used for extraction of mechanical properties of geomaterials. ⢠Chapter 7 provides the findings of the implementation of the specification for extracting modulus from compacted materials using IC from the field studies conducted at four additional test construction sites in Minnesota, Ohio, and Texas. ⢠Chapter 8 discusses the framework for an IC specification along with the rationale for incorporating different items in the draft specification. This chapter also contains the limitations of the proposed process and recommendation for smooth implementation of the specification. ⢠Chapter 9 summarizes the findings and conclusions from this project. Eight appendices are provided to complement these chapters. Appendix A, titled âProposed Standard Specifications and Test Methods to Estimate Mechanical Properties of
Introduction 11 Geomaterials Using Intelligent Compaction,â is printed with this report and contains the following documents: ⢠Proposed Standard Specification for Extracting Modulus of Compacted Geomaterials Using Intelligent Compaction (IC); ⢠Proposed Standard Specification for Quality Management and Design Verification of Earthwork and Unbound Aggregates Using Intelligent Compaction (IC); ⢠Proposed Standard Test Method for Determining Intelligent Compaction Measurement Value (ICMV) Using Intelligent Compaction (IC) Technology; and ⢠Proposed Standard Test Method for Estimating Modulus of Embankment and Unbound Aggregate Layers with Portable Falling Weight Devices. The remaining seven appendices are grouped together in a downloadable PDF file which can be obtained from the NCHRP Research Report 933 webpage at www.trb.org. The PDF file contains: ⢠Appendix B: Experimental Plan for Phase 3 Field Activities; ⢠Appendix C: Review of Literature; ⢠Appendix D: Numerical Modeling of Compaction of Geomaterials; ⢠Appendix E: Extracting Mechanical Properties from IC Data; ⢠Appendix F: Field Study for Implementation and Evaluation of NDT and IC for Quality Acceptance and Design Modulus Verification; ⢠Appendix G: Calibration of Models Using Field Data; and ⢠Appendix H: Mechanical Property Measurements.
