Evaluation of mechanistic-based compaction measurements for earthwork QC/QA.

摘要

Compaction control for subgrade and base materials used in highway construction is typically based on field tests in comparison to laboratory Proctor tests that determine the relationship between dry unit weight and moisture content. The "optimum" moisture content and maximum dry unit weight are established and then a minimum relative compaction value and moisture content range is specified for acceptance during construction. This approach, although widely accepted, does not directly determine the mechanistic properties of the compacted material (i.e., strength or stiffness). The premise for adopting QA/QC tests that determine mechanistic properties is that the QA/QC operations would more directly relate to the design and also provide perhaps more value for ensuring quality as a final product. A further limitation of standard QA/QC practices is that generally not enough information is collected due to limited test frequency to ensure adequate reliability in quality over large areas. Non-homogeneous vertical soil profiles are one aspect of in-situ testing that has largely been ignored.This study addressed these problems by evaluating five mechanistic-based devices in the field and in the laboratory. Field studies were conducted at sites in West Virginia, Iowa, Ohio, New York, and Michigan, to investigate the performance of five mechanistic-based compaction control measurement devices. Laboratory tests were also performed to evaluate relationship between moisture content, density, shear strength, and elastic/resilient modulus. A unique aspect of this research in addition to the field studies is that gyratory compaction samples were used to assess engineering properties of several soils and provided information on moisture content, density, and shear resistance relationships during the compaction process and a sample to test using other methods. Based on the comparison of the five mechanistic-based devices conducted for this study, trends were observed between devices and tradition density measurements, and the results provide data to evaluate the in situ variability of compacted materials. The results of the laboratory study showed that gyratory compacted samples provide useful information to determine mechanistic-based target values for QC/QA practices.