Statnamic Load Testing of High Capacity Marine Foundations-PDF

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The St. George Island Bridge project evaluated high-capacity, 54-inch-diameter, 80-foot-long spun-cast concrete cylinder piles using static, STATNAMIC, and dynamic load testing. Four test piles were compared, with embedded strain gauges measuring behavior during post-tensioning, driving, and load tests.<br /><br />Instrumentation recorded post-tensioning stresses of 760–1,010 psi and indicated some locked-in eccentricity. The measured composite modulus of elasticity was 5,725 ksi. During driving, the gauges captured stress-wave propagation and pile stresses; these measurements agreed well with PDA-derived peak forces.<br /><br />STATNAMIC applies a sustained, smoothly increasing load rather than a brief impact. Its longer loading duration keeps the pile in compression and allows a simpler analysis, while embedded gauges help determine load distribution. Static resistance is derived by accounting for inertia and damping.<br /><br />Compared with static tests, STATNAMIC capacity estimates were within 2% for three piles. The fourth was 9% lower, likely because only two days separated the tests and the pile had not regained its full side-shear capacity. The tests also generally showed good agreement in end-bearing and side-shear estimates, though differences varied by pile.<br /><br />CAPWAP restrike estimates underpredicted static capacity by 9–41%, and its estimates of skin friction and end bearing often differed substantially from measured distributions. Dynamic testing nevertheless remained useful for assessing driving stresses and hammer energy.<br /><br />Overall, the project demonstrated that instrumented STATNAMIC testing can provide reliable capacity and load-distribution information for large marine foundations, with less elaborate reaction equipment than static testing.

Keywords

St. George Island Bridge

STATNAMIC testing

static load test

dynamic load testing

concrete cylinder piles

embedded strain gauges

pile capacity

side shear

end bearing

CAPWAP analysis