LATWAK: Impact Test to Obtain Pile Lateral Static Stiffness
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abstract
The LATWAK test consists of hitting in the horizontal direction the side of a pile on which a horizontal velocity transducer is attached. The blow is delivered with a sledge hammer equipped with a dynamic force transducer. The force time signal from the hammer (input) and the velocity time signal from the pile (output) are recorded during the impact. The experimental mobility curve is obtained as a function of frequency by calculating the modulus of the complex valued ratio of velocity over force using Discrete Fourier Transforms. Theoretically it is assumed that the pile is an elastic member with mass and that the soil can be represented by linear springs and viscous damping. The problem of the steady state forced vibration of the pile in such a soil is solved mathematically. It leads to the theoretical mobility curve for the pile-soil system. The experimental mobility curve obtained in the LATWAK test on the pile is matched with the theoretical mobility curve. A system identification technique is used to match the two curves and to extract the best-fit model parameters, which include the static lateral stiffness K for the pile-soil assembly. To evaluate the usefulness of the method, the lateral stiffness Kp predicted by the LATWAK test on a pile was compared to the lateral stiffness Km measured in a static lateral load test on the same pile. A total of 20 pile load tests and 20 LATWAK tests were performed and used to compare Kp and Km. The results are encouraging. ASCE.
