Common Mistakes in Static Loading-test Procedures and Result Analyses

Abstract

Static loading tests on piles are arranged in many different ways ranging from quick tests to slow test, from constant-rate-of-penetration to maintained load, from straight loading to cyclic loading, to mention just a few basic differences. Frequently, the testing schedule includes variations of the size of the load increments and duration of load-holding, and occasional unloading-reloading events. Unfortunately, instrumenting test piles and performing the test while still using unequal size of load increments, duration of load-holding, and adding unloading-reloading events will adversely affect the means for determine reliable results from the instrumentation records. A couple of case histories are presented to show issues arising from improper procedures involving unequal load increments, different load-holding durations, and unloading and reloading events—indeed, to demonstrate how not to do. The review has shown that an instrumented static loading test, be it a head-down test or a bidirectional test, performed, as it should, in a series of equal load increments, held constant for equal time, and incorporation no unloading-reloading event, will provide data more suitable for analysis than a test performed with unequal increments, unequal load-holding, and incorporating an unloading-reloading event. No useful information is obtained from prolonging the holding time for the maximum load.