Strain Gauge Instrumentation of Spliced Concrete Piles in Soft Alluvial Soils-PPT Presentation

PPT Presentation

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The presentation describes strain-gauge instrumentation and testing of spliced precast concrete piles for a large wharf founded in soft alluvial soils. The project used 36-inch-square piles, typically 120–160 feet long. Because site conditions required piles to be driven in two sections, the team installed vibrating-wire strain-gauge pairs in both sections and connected them across the splice.<br /><br />The testing program combined dynamic testing with a static load test conducted after a 28-day waiting period. The static test reached the reaction frame’s maximum load of 2,500 kips, with 1.25 inches of maximum deflection and 0.25 inches remaining after unloading. Strain measurements were used to estimate load transfer along the pile. The results indicated about 900 kips of end bearing, potentially rising to approximately 1,000 kips after accounting for high frictional resistance in the lower pile segment.<br /><br />The load-deflection response showed no geotechnical failure at 2,500 kips, despite predicted failure estimates of 1,600–2,000 kips. The team concluded that dynamic testing substantially underestimated end bearing and total resistance, while strain gauges helped clarify the load-transfer mechanism and validate full end-bearing behavior.<br /><br />These findings enabled the design team to lengthen piles to use additional end-bearing capacity and increase pile spacing. The revised design reduced the number of piles per bent from 22 to 16 and cut the overall pile quantity by about 34%—approximately 1,100 piles and more than 90,000 linear feet of pile.

Keywords

strain-gauge instrumentation

precast concrete piles

wharf foundation

soft alluvial soils

vibrating-wire strain gauges

dynamic testing

static load test

end bearing

load transfer

pile design optimization