Pile Load Tests: Cyclic Loads and Varying Load Rates

Two series of axial load tests were performed on four 14-in. (356-mm) diam, open-end, steel pipe piles at an interval of about 320 days. Pile lengths of 40 ft or 50 ft (12.2 or 15.2 m) were installed below conductors driven to depths ranging from 115 ft to 320 ft (35 m to 98 m) into a strong underconsolidated clay. Each pile was subjected to as many as 26 tests. Data presented includes: (1) Compression and tension tests; (2) tests performed at different times after driving and after previous tests; and (3) incremental loading and constant rate of loading. Pile capacity increased 40% to 75% when the loading rate increased by three orders of magnitude. The one-way cyclic loading applied in this study did not effect the ultimate capacity, but large displacement began to accumulate when the maximum cyclic load reached 80% of the static capacity.