Study on Elastic Modulus and Recovery Coefficient of Cushioning Materials in Pile Driving

Cushioning materials are one of the most important auxiliary equipments in pile driving whose equality has great influence on the quality of construction. In this paper, the static and dynamic behaviors, mainly focused on elastic modulus and recovery coefficient, of three commonly used cushioning materials of pine wood, asbestos–rubber board, and disk spring are fully discussed by different experiments. The static loading is used to measure the static elastic modulus and recovery coefficient while the methods of back-calculation according to the natural frequency of a cantilever beam and slope of a dynamic stress-strain curve are individually adopted to determine the dynamic elastic modulus, and the dynamic recovery coefficient is measured by making normal impact of the spherule to the base plate. The tests show that the dynamic elastic modulus and recovery coefficient from the dynamic test are more applicable in modeling the actual behavior of cushioning materials in pile driving than is the static. Among these three materials, the disk spring is considered to be the most optimum material in pile driving for its high, steady recovery coefficient (above 0.9).