Coefficient of subgrade reaction of the rubble mound in the foundation of the open pier or the mooring post is identified by the Kalman filtering in conjunction with the transfer matrix method based on the measurement of in-situ experiments of piles. The existing surface clay layer is removed and the dilluvial clay layer is replaced by the rubble mound to shorten the length of the pile above the surface of the foundation deposit. In-situ experiments were carried out for both the existing clayey

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... layer and the rubble mound. Measured data for the inclinometer is differentiated to obtain the moment and integrated to obtain the displacement along the pile, and they are used as the input for inverse analysis. Identified coefficient of the rubble mound using these measurements is less than that of the dilluvial clay under the same level of the loading. Numerical results provide useful information for the design of the open pier and its foundation.