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.