Dynamic Properties of Earth Material during Rolling Compaction
I. RESEARCH PROBLEM STATEMENT
The rolling compaction of earth material for roadway construction is one of the primary construction activities to prepare subgrade and build embankment, base, and subbase of highways. Current standards of state highway agencies (SHA) require contractors to build uniform pavement structural layers, but with no means to check and quantify it continuously. Usually, the minimum spacing of 1000 ft. for dry density and moisture content as quality assurance tests at selected point locations is expected to represent the entire section. The implementation of the intelligent compaction technology has the potential to address this problem. Roller Integrated Compaction Monitoring (RICM) [i.e., intelligent compaction (IC) or continuous compaction control (CCC)] refers to the compaction of road materials, including subgrade soils, aggregate bases, stabilized materials, and asphalt-paving materials, using modern rollers equipped with an integrated IC or CCC measuring system. The technology continuously records the roller’s location and reaction to layer stiffness and plots the result during compaction operations, so the field-generated data and plots can provide useful information for quality control/quality acceptance (QC/QA) of compaction operations.
However, the current intelligent compaction technology depends solely on the roller measurement values (MVs), which “are a composite reflection of typical base, subbase, and subgrade structures with a surface to top-of-subgrade thickness of less than approximately 1 m (3.3 ft.)” (1). The roller MVs are also “influenced by layer thickness, relative stiffness of layers, vibration amplitude, and drum/soil interaction issues” (1). These characteristics have become the obstacle for the further advancement and implementation of IC technology. Possible solutions to overcome this obstacle require a better understanding of the dynamic properties of earth material during rolling compaction. Such an understanding is essential to advance the current IC technology and make it implementable with maximum benefits for highway construction. In order to achieve this objective, a proper laboratory testing procedure that simulates rolling compaction should be identified or developed, and the testing procedure should be verified and validated with various earth materials. Through a comprehensive laboratory study, proper parameters that can better reflect the properties of earth material during rolling compaction can be identified. These parameters should be measurable during the field rolling compaction to improve or modify current integrated IC or CCC measuring systems.
There is a big difference in response to rolling compaction between un-compacted and compacted earth materials. Loose earth materials will be compacted and structured by absorbing the compaction energy (work) exerted by rolling compaction through the change of internal microstructure. Limited studies indicate that the ability of earth materials to absorb external energy is affected by the material types, conditions, and its environment (2). This capability of earth materials can be investigated through unsaturated/saturated soil mechanics. Finally, this study will be of paramount importance for understanding the dynamic properties of various earth materials during rolling compaction.
II. LITERATURE SEARCH SUMMARY
A number of different searches were conducted in the TRIS databases and the TRB Research in Progress database for this topic or for items that seemed to fit closely with this topic. The results indicate that no research work has directly addressed this need although some seem related, but not exactly the same.
· Intelligent Compaction System. NCHRP report 676, 2010
· Zhang, Z., et al., “Absorbed Energy and Compacted Cohesive Soil Performance”, Geotechnical Testing Journal, ASTM, GTJODJ, Vol. 28, No. 4, July 2005, pp. 404-409.
III. RESEARCH OBJECTIVE
The objective of the research is to identify or develop a laboratory testing procedure that simulates rolling compaction of earth materials in order to study their properties during this dynamic process. Based on the study findings, recommendations to improve current IC technologies are expected. The improved IC technology should be able to measure the properties of a layer being compacted. It can be predicted that deformation or deflection measurements on compacted layers might be needed in addition to resistance. Therefore, this study should evaluate and compare various in-situ measuring mechanisms available. Prototype development for this study should seek the participation of manufacturers.
The study will encompass, but will not be limited to, the following tasks:
- Perform literature review: state of the art and state of the practice.
- Develop and prove the concept for testing protocols. Approval from research review panel is needed for acceptance.
- Modify or develop testing device/procedures.
- Test various earth materials.
- Make recommendations for field IC implementation. An interim report is needed to summarize achievements up to this point.
- Work with manufacturers to build prototype.
- Conduct field testing to prove the feasibility.
- Develop test procedures in AASHTO format.
- Develop implementation recommendations.
- Write a final report to document the research effort and final results.
A successful proposal should provide and elaborate on the details of the tasks listed.
IV. ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD
An estimate of the funds necessary to accomplish the objectives stated in Section V above is $500,000.
An estimate of the number of months of research effort, including three months for preparation of a draft final report, necessary to the accomplishment of the objectives presented in Section V above is 36 months.
V. URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION
Building uniform pavement structure layers has always been the dream of highway engineers as it will secure a long pavement service life. Improving the construction quality of earth materials in highway construction will help in realizing this dream and have a fundamental impact on highway engineering since it will allow state highway agencies to use highway funds more cost effectively. The successful execution of this study will make IC technology a more suitable tool for state highway agencies to continuously check and quantify the compaction quality of earth material. It will promote and expedite the implementation of intelligent compaction technology in highway construction so a better construction quality of highways can be achieved. Therefore, the potential for a payoff from the achievement of project objectives is significant and cannot be overestimated.
The TRB committees Soils and Rock Instrumentation (AFS20) and Engineering Behavior of Unsaturated Soils (AFP60), who are drawn from many sectors of the transportation community, have identified this problem as a high priority for those involved in the construction of transportation infrastructure. One of the interests of these committees is the in-situ measurement of performance related properties of soil and layered systems and applying these measurements to the design, construction, and monitoring of transportation facilities. Continuous compaction control and intelligent compaction have been identified by these committees as a technology ready for greater implementation, but in need of some focused, well-defined research that will fill the remaining gaps preventing widespread implementation.