Embankment Quality, Phase 4: Application to Unsuitable Soils (TR-492)

Principal Investigator:

David White, djwhite@iastate.edu (other projects)

Co-Principal Investigator:

• Charles Jahren, cjahren@iastate.edu (other projects)

Student Researchers:

• Joels Malama, joelscm@iastate.edu
• Brett Larsen

Other Authors: David J. White, Brett W. Larsen, Charles Jahren, Joels Malama

Project Status: In Progress

Start Date: 05/15/2003
End Date: 10/31/2007

Reports:

• 10/31/2007, http://www.ctre.iastate.edu/reports/embankment4.pdf 6.5 mb (*pdf)

Research Objective: The Quality Management Earthwork (QM-E) special provision was implemented on a pilot project to evaluate quality control (QC) and quality assurance (QA) testing in predominately unsuitable soils. Control limits implemented on this pilot project included the following: 95% relative compaction, moisture content not exceeding +/- 2% of optimum moisture content, soil strength not exceeding a dynamic cone penetrometer (DCP) index of 70 mm/blow, vertical uniformity not exceeding a variation in DCP index of 40 mm/blow, and lift thickness not exceeding depth determined through construction of control strips. Four-point moving averages were used to allow for some variability in the measured parameter values.

Management of the QC/QA data proved to be one of the most challenging aspects of the pilot project. Implementing use of the G-RAD data collection system has considerable potential to reduce the time required to develop and maintain QC/QA records for projects using the QM-E special provision. In many cases, results of a single Proctor test were used to establish control limits that were used for several months without retesting. While the data collected for the pilot project indicated that the DCP index control limits could be set more tightly, there is not enough evidence to support making a change. In situ borings, sampling, and testing in natural unsuitable cut material and compacted fill material revealed that the compacted fill had similar strength characteristics to that of the natural cut material after less than three months from the start of construction.

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