Case Study: Load Transfer Analysis on an Instrumented Augercast Pile Using EDC Strain Gauges and Geokon Rebar Strainmeters-Paper

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This case study compared Embedded Data Collector (EDC) strain gauges with Geokon vibrating-wire rebar strainmeters in an 18-inch-diameter, 77.6-foot-long augercast pile at the DC Water Main Pump Station project in Washington, D.C. Both systems were installed at several depths on a central Dywidag bar to measure strain and estimate load transfer during an axial compression test.<br /><br />A casing extended to the pile’s proposed cutoff elevation to eliminate shaft friction in the overburden. The pile was tested under ASTM D1143 procedures, reaching a maximum load of 480 kips (2,135 kN), held for one hour. Strains were converted to loads using the pile’s cross-sectional area and estimated concrete elastic modulus.<br /><br />At comparable sensor elevations, EDC and Geokon load measurements generally agreed within 5–15%; the difference narrowed to about 5% at maximum load. Their estimated end-bearing loads were also close: 88 kips (391 kN) from EDC and 90 kips (400 kN) from Geokon. At maximum load, pile movement was 0.645 inches (16.3 mm), just below the 0.65-inch Davisson failure displacement.<br /><br />The study concludes that EDC measurements were consistent with the established Geokon system, making EDC a viable alternative for pile monitoring. EDC’s advantages include wireless data collection and the ability to capture both static and dynamic strains. The authors note that differences between systems may reflect sensor locations and assumptions used to convert strain to load.

Keywords

Embedded Data Collector

EDC strain gauges

Geokon vibrating-wire rebar strainmeters

augercast pile

pile load testing

ASTM D1143

load transfer

end-bearing load

Davisson failure displacement

wireless data collection