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Accession Number PB2012-114370
Title Field Verification of Undercut Criteria and Alternatives for Subgrade Stabilization- Coastal Plain.
Publication Date Jun 2012
Media Count 248p
Personal Author M. A. Gabr R. H. Borden S. C. Pyo T. D. Cowell
Abstract The North Carolina Department of Transportation (NCDOT) is progressing toward developing quantitative and systematic criteria that address the implementation of undercutting as a subgrade stabilization measure. As part of this effort, a laboratory study and numerical analysis were performed from 2008 to 2010 with the results providing proposed criteria for undercutting under various roadway site conditions and the adequacy of stabilization measures typically employed if undercut was deemed necessary. These criteria provide provisions for discerning possible rutting and pumping of the subgrade under construction loading, and provide response and subgrade stiffness under repeated loading of 10,000 cycles. The work in this report is focused on performing full-scale testing in the field on instrumented unpaved roadway sections to collect data for the validation of guidelines developed from the laboratory and modeling study. Four 16 feet wide by 50 feet long stabilized test sections were built on poor subgrade soils encountered in the Coastal Plain region of North Carolina. One test section encompassed undercutting and replacement with select material (Class II), the second and third test sections included reinforcement using a geogrid and geotextile, respectively, in conjunction with undercutting and replacement with ABC (Class IV), and a fourth test section included cement treatment of the soft subgrade soil. Full-scale testing was conducted on the test pad by applying 1000 consecutive truck passes using a fully loaded tandem-axle dump truck over a period of four days. During this time visual observations were noted and measurements were collected regarding rut depth, vertical stress increase at the base/subgrade interface, and subgrade moisture content with truck passes. Once trafficking was completed, the test pad was re-graded and proof roll testing was performed to look for signs of pumping and rutting. Based on the field results, the proposed undercut criteria are evaluated in regards to the ability to discern the need for undercutting as well as predict the performance of the stabilized test sections. Finally, a performance cost analysis is conducted to illustrate the relative cost of each stabilization measure in relation to the measured performance (rutting) such that an informed decision on cost-effective subgrade stabilization can be made.
Keywords Cement stabilization
Earth pressure cells
Full-scale testing
Performance cost

Source Agency Federal Highway Administration
NTIS Subject Category 89G - Construction Materials, Components, & Equipment
85H - Road Transportation
50C - Construction Equipment, Materials, & Supplies
Corporate Author North Carolina State Univ. at Raleigh. Dept. of Civil, Construction and Environmental Engineering.
Document Type Technical report
Title Note N/A
NTIS Issue Number 1225
Contract Number N/A

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