A Case Study for Applying the Incremental Rigidity Method to Instrumented Static Load Tests Performed on All-Steel Piles-PPT Presentation

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The presentation evaluates the incremental rigidity (I.R.) method for interpreting strain-gauge data from static load tests on all-steel piles. Conventional analysis calculates pile force using assumed steel modulus and area. Variations in material properties, pile geometry, gauge calibration, load-cell accuracy, and local conditions can produce implausible results, such as negative shaft resistance or unexplained force losses.<br /><br />For steel piles, the I.R. relationship assumes the force–strain response is linear, allowing internal forces to be estimated from changes in load and strain without relying solely on assumed values for modulus and area. The method was applied to three test cases in different soil and rock conditions, including glacial till, soft sandy clay, shale, sand and gravel, siltstone, and clay fill.<br /><br />Compared with conventional calculations, I.R. generally reduced the variability of unit shaft and toe resistance estimates. It also aligned more closely with CAPWAP results for the proportion of shaft resistance; conventional analysis could overestimate shaft resistance. Overall, the I.R. method provided more credible distributions of shaft and toe resistance and helped recover strain-gauge data that might otherwise have been discarded.<br /><br />The presenter concludes that the results support using I.R. for steel piles, despite the additional analysis and some subjectivity. Careful review of site- and test-specific information is recommended to validate the results.

Keywords

incremental rigidity

strain-gauge data

static load tests

steel piles

shaft resistance

toe resistance

CAPWAP

force-strain response

pile analysis

load calibration