Role of Advanced Technology - Resolve Inherent Dichotomy in High Strain Dynamic Testing-Paper

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The paper addresses a key limitation of conventional high-strain dynamic testing (HSDT): pile shaft (skin) and toe (tip) resistance may be maximally mobilized at different stages of driving. Because traditional external gauges measure only at the pile top and typically estimate resistance components indirectly, they may not reliably separate skin and tip capacity or combine their peak values.<br /><br />The authors describe embedded data collectors (EDCs) installed at both the top and tip of concrete piles. These sensors record strain and acceleration during each hammer blow. Analyzing the measurements with the FDOT method, engineers can estimate tip and skin resistance independently, along with their settlements, for individual blows. Tip resistance is derived from tip measurements using energy-based analysis, while skin resistance is calculated from wave-equation analysis of pile segments.<br /><br />The paper proposes “superposition”: combining the best-mobilized tip resistance, generally observed near the end of initial driving (EOID), with the best-mobilized skin resistance, generally observed at the beginning of restrike (BOR). This aims to address the mismatch in mobilization timing and provide a more representative total pile capacity. Three field examples illustrate how resistance and settlement data can reveal whether apparent changes reflect soil freeze or relaxation, or incomplete mobilization by the hammer.<br /><br />The authors also highlight potential applications in evaluating scour effects, predrilled or preformed zones, uplift capacity, pile integrity, and driving stresses. They argue that independent resistance estimates can support separate resistance factors for tip and skin, comparison with static load tests, and broader quality assurance through testing every pile. Overall, the paper presents top-and-tip EDC instrumentation and FDOT analysis as a means to improve pile-capacity assessment, construction decisions, and design efficiency.

Keywords

high-strain dynamic testing

pile capacity

skin resistance

tip resistance

embedded data collectors

strain and acceleration

FDOT method

wave-equation analysis

pile driving

superposition