Rapid Lateral Load Testing of Deep Foundations-Article

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The paper presents a rapid method for testing the lateral response of deep foundations. A Statnamic device uses pyrotechnic combustion to apply a load pulse, typically lasting about 100 milliseconds and always less than one second. Unlike conventional static tests, this approach requires no reaction system and can efficiently generate very large loads. Measurements of force, acceleration, displacement, and foundation strain are collected with high-speed instrumentation.<br /><br />Because rapid loading generates inertia and damping forces as well as static soil resistance, the results must be interpreted dynamically. The paper proposes a practical single-degree-of-freedom model that accounts for foundation mass, viscous damping, and nonlinear static stiffness. The model is fitted to measured force and displacement histories to estimate static and dynamic resistance. Although the interpretation is not unique, its limited number of parameters makes it suitable for routine comparison with familiar static test results.<br /><br />Four case histories compare rapid tests with conventional lateral loading tests: drilled shafts at Charleston, rock-socketed shafts at Auburn, and a pile group at Pascagoula. In each case, the derived static response agreed reasonably well with measured static behavior, including nonlinear stiffness and failure resistance. The tests also provided information about damping, displacement patterns, and subsurface rotation or bending.<br /><br />Rapid testing offers speed, safety advantages, and the ability to measure rate-dependent soil resistance relevant to transient events such as earthquakes, wind gusts, and vessel impacts. Its limitations include sensitivity to soil-dependent rate effects, inability to measure creep under sustained loading, and the need to account for inertia and use high-speed data acquisition. Overall, the method appears to provide reliable estimates of static lateral response while also revealing dynamic resistance.

Keywords

Statnamic test

lateral response

deep foundations

pyrotechnic loading

dynamic interpretation

single-degree-of-freedom model

viscous damping

nonlinear stiffness

drilled shafts

pile group