Current practice for the geotechnical design of micropiles on federal bridge projects includes two key components. First, minimum bond lengths are established based on presumptive values of the grout-to-ground bond strength. Second, given the uncertainty in the soil parameters the design is often verified by performing static load tests on selected test piles generally at the start of construction. Presumptive bond strengths can range up to a factor of three for a given soil type, and their selection often involves significant engineering judgment. Static load tests can be costly constituting 10 to 25 percent of the total foundation cost depending on the size of the project. This presentation provides an overview of a novel in situ concept called the Borehole Plug Test that could potentially address the issues above. The test involves casting a small-scale grout plug at the bottom of a geotechnical borehole used for site investigations and load testing the plug to assess the bond strength and load transfer behavior in a site-specific soil. Results of a field trial of the test are presented and some fundamental aspects of the behavior are discussed that need further investigation.
AEG New England has now moved to an every-other-month meeting schedule. The next speaker and topic will be posted the end of December. Please check back at that time for meeting details