Abstract: In the current code, the determination of the correction coefficient of dynamic penetration needs to consider the influence of the measured number of hammer blow, which is rarely studied in the industry. During a blow, the dynamic penetration drop hammer and the probe rod transfer the mechanical energy through collision. Based on the one-dimensional collision theory, if the coefficient of restitution is not zero, the two will continue to collide under the action of gravity and soil resistance. The calculation method for the rod length correction coefficient under three calculation schemes is derived: only calculating the energy of the probe rod after the first collision, calculating the energy of the drop hammer and probe rod after the first collision, and calculating the finite number of collisions after the first collision. The results show that whether the soil resistance is taken into account in the collision process or between the two collisions of a single blow has an influence on the calculation of the rod length correction factor. The calculation function for calculating the sum of the energy of the falling weight and the probe rod after the first collision is used to fit the rod length correction coefficient in the current code, and the determination coefficients of heavy and super heavy are 0.993 5 and 0.975 1 respectively. Using the calculation method calculating the finite number of collisions after the first collision, only the influence of resistance of soil to probe rod between two collisions is considered. The calculated rod length correction coefficient decreases with the increase of the number of blows, when the coefficient of restitution is no greater than 0.3.

Key words: dynamic penetration test, correction coefficient, one-dimensional collision theory, measured number of hammer blow, resistance of soil to probing rod