Mechanical impedance method and stiffness calculation formula for detecting the foundation pile

The effect applying the mechanical impedance method to test the structural pile foundation is the same perfect, simple and strong as its theory. However, the measured velocity-admittance curve approaching the low frequency section is distorted by taking this method because of the poor low-frequency characteristics of the test instruments. It has been making the calculating results wrong by using the pile stiffness formula although this formula has been adopted by the national standard for a long time. After improving the test condition, the real and correct velocity admittance curve is obtained. Moreover, a new formula of calculating the pile stiffness is further deduced and proposed in this paper. It has been proved to be correct, valid and feasible in our more than ten-year´s practice and can be further popularized in our country.