Transportation agencies utilize metal-tensioned reinforcing systems for a number of geotechnical applications, including construction and repair of foundations, retaining structures, and excavated and natural soil and rock slopes. Under NCHRP Project 24-13, researchers identified and refined tools to predict the remaining useful life of existing installations of metal-tensioned systems, as well as the design life of new installations. The result of this research was NCHRP Report 477 (2002) titled Recommended Practice for Evaluation of Metal-Tensioned Systems in Geotechnical Applications. The recommended practice includes a suite of nondestructive testing (NDT) methods combined with a refined service life prediction model that allows practitioners to effectively evaluate and manage field installations of metal reinforcements. In 2003, the firm McMahon & Mann Consulting Engineers, P.C. (MMCE) of Buffalo, NY was retained by the New Hampshire Department of Transportation to undertake an NDT condition assessment program and service life evaluation of a 30+ year old rock reinforcement installation along I-93 in Woodstock, NH. The Principal Investigator for the NH project served as co-PI for the NCHRP work referenced above, and conducted the project in accordance with NCHRP Report 477. A report of the 2003 NH project is available at http://nh.gov/dot/materialsandresearch/research/projects/13733l.htm . To verify and refine the NDT results obtained during the 2003 project, a program of invasive testing and evaluation is now proposed at the site. It is hoped that improved correlation of NDT results will provide transportation agencies with enhanced confidence in applying such results in the future, leading to a decrease in invasive testing and associated costs.

The work proposed under this pooled-fund study consists of validation of NDT results for the condition assessment of rock reinforcements through limited destructive testing including lift-off tests and exhumation of selected reinforcements. The proposed project will take advantage of extensive NDT results already obtained in accordance with NCHRP Report 477 at an interstate site in New Hampshire. Verification of NDT results is unique and of significant value to the transportation community, enhancing the ability of engineers to perform accurate service life estimates from NDT results in the future. The conclusions and recommendations contained in NCHRP Report 477 state that ¿uncertainty about the precision, accuracy, sensitivity, reliability, and limitations of the NDT remain. There is a need to examine the application of NDT under field conditions where corrosion conditions and details of distressed elements are known.¿ It is expected that this pooled-fund study will contribute to improved confidence in NDT, reducing the need for invasive testing in the future and lowering the overall costs and uncertainty associated with the condition assessment of metal reinforcements in geotechnical applications.

The proposed pooled-fund project includes invasive testing of selected rock bolts and tendons to verify results obtained at the I-93 site in 2003, including NDT, condition assessment, and service-life estimates. Invasive testing will include lift-off tests; and physical, chemical and metallurgical testing on steel and grout samples retrieved from exhumed reinforcements. Replacement bolts will be installed prior to invasive testing of the reinforcements. It is proposed that two of the replacement bolts be instrumented with strain gages to facilitate future monitoring. Details of the testing program are summarized as follows: A total of five rock bolts will be selected for lift-off tests and subsequently exhumed. In addition, two tendon reinforcements will be exhumed. The test program will include some reinforcements with questionable condition, and some reinforcements considered to be in good condition, based on the results from NDT. It is acknowledged that exhuming reinforcements will be a difficult task and the chances for successfully exhuming reinforcements are uncertain. Reinforcements that are exhumed will be measured, sketched, photographed and carefully stored for examination and testing, including an evaluation of corrosion, loss of cross section, or kinks/bends, as well as assessment of the grout quality. Additional samples will be used for metallurgical analysis and physical testing. NDT tests performed during Phase I will be repeated on elements selected for invasive testing. In addition, the UK firm AMEC Group Ltd. will be invited to the site to perform their patented GRANIT integrity test on the same rock reinforcements tested previously, providing a useful comparison with NDT results described in the NCHRP report. Data collected during this project will be analyzed and compared to NDT and service-life prediction results, and reported along with conclusions and recommendations for refined interpretation of NDT results in the future. Please refer to the proposal linked to this solicitation for more detail.

A one-time, minimum pledge of $10 K is requested. However, pledges in any amount will be accepted.