On uplift capacity of aged grillage foundations

Eight full-scale field uplift tests were conducted in granular soils on steel grillage foundations for lattice transmission line towers that had been in place since 1929, 1947, and 1958. Both the site conditions and load tests were documented extensively. For capacity evaluation, the vertical shear model is appropriate, but cautions are warranted for evaluating the stress state and properties of both the backfill and native host soil. The test results showed that, although backfill compaction was minimal or nominal at placement, probable overconsolidation and aging have improved the backfill properties, making them more like those of the native host soil. This positive aging effect on capacity could have significant economic impact on many planned upgrading studies in progress around the world.