A Study of Anchorages for Transmission Tower Foundations

Abstract

A number of uplift tests have been conducted on anchors proposed for use to support high voltage transmission line towers both for the conventional four legged structure and for the guyed-type structure with a single central footing. Tests were carried out at seven sites, six in the Toronto-Barrie Area and one at Thunder Bay, Ontario. The soil conditions included very dense till, soft clay up to 130 ft (39.62 m) in depth, dense sand and gravel and loose to compact silty sand. The test installations included both power installed multi-helix anchors and grouted anchors with a single reinforcing rod. These were installed at various depths. In the very deep clay only multi-helix anchors were tested. Most of the tests were in uplift on anchors installed vertically. A few group tests were conducted both in uplift and compression. The results of all of the tests are presented along with fairly detailed information on the properties of the soil at each site. An attempt to analyze the results of the helix anchor tests using simplified bearing theory was made. The grouted anchor tests were analyzed using either frictional or adhesive bond theory depending on the soil type. The results indicate that the theories using conventional soil properties provide reasonable design parameters for initial planning. Further confirmation by fullscale testing, however, is essential.