Proceeding of the 2018 DFI-EFFC International Conference on Deep Foundations and Ground Improvement, Rome, Italy, (DFI, EFFC)
A Call for Code Revisions for High Capacity Micropiles in Rock
Anthony C. Barila, P. E., Lawrence F. Johnsen, P. E. and John McKinnon, Project Manager
Today’s micropiles are not the pali radici of Dr. Lizzi. The availability of relatively inexpensive but high strength pipe manufactured for the oil drilling industry has revolutionized the design of high capacity rocksocketed micropiles. However, the growth of this sector of the micropile market is constrained by the governing codes which unnecessarily limit design stresses, do not account for the difference in material properties of grout and concrete, and are silent on issues particular to rock socketed micropiles. Hub Foundation has performed numerous pile load tests of rock-socketed micropiles in compression (up to 1010 tons or 8.9 MN) and tension (up to 458 tons or 4.1 MN). This paper will present several of these test results with plots of movement at the top of pile versus load and plots of load distribution within the rock sockets using data from strain gauges. These test results along with several publications from other authors will provide the basis to reevaluate the various codes used in the U.S. and Europe in regards to the issues of design stresses, grout cover, bar spacing, strain compatibility, video inspection and load shedding. This evaluation process was initiated by Barila and McKinnon at the 2017 ISM in Vancouver with the presentation of "33 Congress Square - A Case Study". This was followed with a publication in the May/June 2017 edition of Foundation Drilling, "33 Congress Square - A Case Study and Call for Code Revisions".
|article #3006; publication #1040 (ROME-2018)|